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Document:	VAX FORTRAN Language Reference Manual (Ver 5.0)
Order Number:	AA-D034E-TE
Revision:	0
Pages:	459
Original Filename:

OCR Text

Language Reference Manual

Order Number: AA-D034E-TE

VAX FORTRAN
Language Reference Manual
Order Number : AA-D034E - TE

June 1988
This manual details the VAX FORTRAN programming language as implemented
for VMS systems .

Revision/Update Information:

This revised manual supersedes
Programming in VAX FORTRAN (order
number AA-00340-TE) .

Operating System and Version:

VMS Version 5.0 or higher

Software Version :

VAX FORTRAN Version 5 .0

digital equipment corporation
maynard, massachusetts

First Printing, September 1984
Revision, June 1988
The information in this document is subject to change without notice and
should not be construed as a commitment by Digital Equipment Corporation .
Digital Equipment Corporation assumes no responsibility for any errors that
may appear in this document .
The software described in this document is furnished under a license and may
be used or copied only in accordance with the terms of such license .
No responsibility is assumed for the use or reliability of software on equipment that is not supplied by Digital Equipment Corporation or its affiliated
companies.
Copyright © 1984, 1988 by Digital Equipment Corporation
All Rights Reserved.
Printed in U.S.A.
The postpaid Reader's Comments forms at the end of this document request
the user' s critical evaluation to assist in preparing future documentation.
The following are trademarks of Digital Equipment Corporation :
DEC
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~U~UIJ~UTM
ZK-4671

Contents
PREFACE

xvii

NEW AND EXPANDED LANGUAGE FEATURES

xxi

CHAPTER 1

INTRODUCTION TO VAX FORTRAN

1-1

1.1

ELEMENTS OF FORTRAN SOURCE PROGRAMS
1 .1 .1
Program Units
1.1.2
Statements
1.1.3
Symbolic Names
1.1.4
Comments

1-2
1-2
1-2
1-5
1-7

1.2

CHARACTER SET

1-8

1.3

CODING RULES
1.3.1
Fixed-Format Lines
1 .3 .2
Tab-Format Li nes
1.3.3
Statement Label Field
1.3 .3.1
Comment Indicator • 1-13
1.3 .3 .2
Debu gging Statement Ind icator • 1- 14
1.3.4
Continuation Indicator Field
1.3.5
Statement Field
1.3.6
Sequence Number Field

1-9
1-10
1-11
1-13

1-14
1-14
1-15

COMPILATION CONT RO L STATEME NTS
1.4.1
DICTIONARY Statement
1 .4.2
INCLUDE Statement
1 .4 .3
OPTIONS Statement

1-1 5
1-1 5
1-17
1-18

1 .4

iii

DATA TYPES, DATA ITEMS, AND EXPRESSIONS

2-1

2.1

DATA TYPES
Storage Requirements
2.1.1
2.1.2
VAX Implementations of REAL*S

2-1
2-2
2-4

2.2

DATA ITEMS
Constants
2.2.1

2-4
2-5

CHAPTER 2

2 .2 . 1. 1
2 .2 . 1.2
2.2.1.3
2.2. 1.4
2.2.1.5
2.2.1 .6
2.2.1.7
2.2.2

2.2.6
2.3

Data Type by Specification • 2-23
Data Type by Implication • 2-24

2-24

Arrays

2.2.3.1
2.2.3.2
2.2.3.3
2.2 .3 .4
2.2.3 .5
2.2.3.6
2.2.3.7
2.2.4
2.2.5

2-22

Variables

2 .2 .2 . 1
2 .2.2.2
2.2 .3

Integer Constants • 2-5
Real Constants• 2-8
Complex Constants • 2-13
Octal and Hexadecimal Constants • 2-15
Logical Constants • 2-18
Character Constants • 2-18
Hollerith Constants • 2-19

Array Declarators • 2-25
Array Subscripts • 2-27
Arrangement of Array Elements in Storage• 2-27
Data Type of an Array • 2-29
Array References without Subscripts • 2-29
Adjustable Arrays • 2-29
Assumed-Size Arrays • 2-30

Character Substrings
Records
Arrangement of Records in Storage • 2-33
2 .2 .5.1
References to Record Fields • 2-36
2.2.5.2
Terminology Used to Refer to Data Items

EXPRESSIONS
2.3.1
Arithmetic Expressions
2.3.1.1
Using Parentheses• 2-44
2.3.1.2
Data Type of an Arithmetic Expression • 2-45
Character Expressions
2.3.2
2.3.3
Relational Expressions
2.3.4
Logical Expressions

2-30
2-31

2-39
2-42
2-42

2-47
2-48
2-49

CHAPTER 3

ASSIGNMENT STATEMENTS

3-1

3.1

ARITHMETIC ASSIGNMENT STATEMENT

3-1

3.2

LOGICAL ASSIGNMENT STATEMENT

3-4

3.3

CHARACTER ASSIGNMENT STATEMENT

3-4

3.4

A GGREGATE ASSIGNMENT STATEM ENT

3-6

3.5

ASSIGN STATEMENT

3-7

SPECIFICATION STATEMENTS

4-1

4.1

BLOCK DATA STATEMENT

4-2

4.2

COMMON STATEMENT

4-3

4.3

DATA STATEMENT

4-5

4.4

DATA TYPE DECLARATION STATEMENTS
4.4.1
Numeric Type Declaration Statements
4.4.2
Character Type Declaration Statements

4-8
4-8
4-10

4.5

DIMENSION STATEMENT

4-12

4.6

EQUIVALENCE STATEMENT
4.6.1
Making Arrays Equivalent
4.6.2
Making Substrings Equivalent
4.6.3
EQUIVALENCE and COMMON Interaction

4-13
4-14
4-17
4-20

4.7

EXTERNAL STATEMENT

4-21

4.8

IMPLICIT STATEMENT

4-22

CHAPTER 4

4.9

INTRINSIC STATEMENT

4-23

4.10

NAMELIST STATEMENT

4-24

4.11

PARAMETER STATEMENT

4-26

4.12

PROGRAM STATEMENT

4-28

4 .13

RECORD STATEMENT

4-29

4.14

SAVE STATEMENT

4-30

4.15

STRUCTURE DECLARATION BLOCK
4.15.1
Structure Declaration
4.15.2
Substructure Declarations
4.15.3
Union Declarations

4-31
4-33
4-38
4-38

4.16

VOLATILE STATEMENT

4-41

CHAPTER 5 CONTROL STATEMENTS
5.1

CALL STATEMENT

5-2

5.2

CONTINUE STATEMENT

5-3

5.3

DO STATEMENTS
5.3.1
Indexed DO Statement
5.3.1.1
DO Iteration Control • 5-5
5.3.1.2
Nested DO Loops • 5-7
5.3.1 .3
Control Transfers in DO Loops• 5-8
5.3 . 1.4
Extended Range • 5-9
5.3.2
DO WHILE Statement

5-3
5-4

END DO STATEMENT

5-11

5.4

5-1

5-9

5.5

END STATEMENT

5-12

5.6

GO TO STATEMENTS
Unconditional GO TO Statement
5.6.1
Computed GO TO Statement
5.6.2
Assigned GO TO Statement
5.6.3

5-12
5-13
5-13
5-14

5.7

IF STATEMENTS
Arithmetic IF Statement
5.7.1
Logical IF Statement
5.7.2
Block IF Statements
5.7 .3
Statement Blocks • 5-21
5.7.3.1
Block IF Examples • 5-2 1
5.7.3.2
Nested Block IF Constructs • 5-23
5.7.3.3

5-15
5-16
5-17
5-17

5.8

PAUSE STATEMENT

5-24

5.9

RETURN STATEMENT

5-25

5.10

STOP STATEMENT

5-27

CHAPTER 6

SUBPROGRAMS -

6.1

6.2

SUBROUTINES AND FUNCTIONS

6-1

SUBPROGRAM ARGUMENTS
6.1 .1
Actual Argument and Dummy Argument
Association
6. 1. 1. 1
Adjustable Arrays • 6-3
6. 1. 1.2
Assumed-Size Arrays • 6-6
6 . 1. 1.3
Passed-Length Character Arguments • 6-7
6. 1. 1.4
Character and Hollerith Constants as Actual
Arguments • 6-8
6. 1.1 .5
Alternate Return Arguments• 6-9
6.1.2
Built -In Functions
6 . 1.2 . 1
Argument List Built -In Funct ions • 6- 9
6 . 1.2 .2
%LOC Built-In Function • 6-1 1

6-2

USER-WRITTEN SUBPROGRAMS
6.2.1
Statement Functions

6-11
6-12

6-2

6- 9

vii

6.2.2

Function Subprograms

6 .2.2 . 1
6.2 .2 .2
6.2 .2 .3

6.2.3
6.2.4

Subroutine Subprograms Statement
ENTRY Statement

6.2.4 . 1
6.2.4.2

6.3

6.3.2

viii

6-25
6-25

Generic References to Intrinsic Functions • 6- 26
Using Intrinsic Function Names• 6-28

6-30

Character Functions • 6-30
Lexical Comparison Functions• 6-32

1/0 STATEMENTS

7-1

COMPONENTS OF 1/0 STATEMENTS
7. 1 . 1
Control List

7-1

7.1 .2

7.2

6-1 8
6-21

ENTRY Statements in Function Subprograms • 6-22
ENTRY Statements in Subroutine Subprograms • 6-24

Character and Lexical Comparison library Functions

6.3.2 . 1
6.3.2.2

7.1

SUBROUTINE

FORTRAN INTRINSIC FUNCTIONS
6.3 .1
Intrinsic Function References

6.3. 1. 1
6 .3 . 1.2

CHAPTER 7

6-1 5

Logical and Numeric Functions • 6- 15
Character Functions• 6-15
Function Reference • 6-16

7 . 1. 1. 1
7 . 1. 1.2
7 . 1.1 .3
7 .1.1 .4
7 . 1 . 1 .5
7. 1 . 1 .6
7 . 1. 1.7
7 . 1 . 1 .8
7.1.1.9
7 . 1. 1. 10
1/0 list
7. 1.2. 1
7 . 1.2 .2

7-2

Syntax Rules for Control-List Parameters • 7- 3
Logical Unit Specifier • 7-3
Internal File Specifier• 7-4
Format Specifiers• 7-4
Nam elist Specifier • 7- 5
Record Specifier • 7-6
Key-Field -Value Specifier • 7-6
Key-of-Reference Specifier • 7-9
1/0 Status Specifier• 7-9
Transfer-of-Control Specifiers • 7-10

7-11
Simple List Elements • 7-12
Implied-DO Lists in 1/0 Statements • 7-13

READ STATEMENTS

7-15

7.2.1

7.2.2

7. 2.3

7.2.4

Sequential READ Statements
7-15
7 .2 . 1 . 1
Formatted Sequential READ Statement • 7-16
7 .2.1 .2
List-Directed Sequential READ Statement• 7-17
7 .2 . 1.3
Namelist-Direct ed Sequent ial RE A D Statem ent • 7- 20
7 .2 . 1.4
Unformatted Sequential READ Statement • 7-25
Direct Access READ Statements
7-26
7 .2 .2.1
Formatted Direct Access READ Statement • 7-26
7.2.2.2
Unformatted Direct Access READ Statement• 7-27
Indexed READ Statements
7-28
7 .2 .3 . 1
Formatted Indexed READ Stat ement• 7-29
7 .2 .3. 2
Unformatted Indexed RE A D Statement • 7- 30
7-31
Internal READ Statement
7 .2.4 . 1
Formatted Internal READ Statement • 7-31
7 .2.4 .2
Li st-Directed Internal REA D Statement • 7-32

7.3

WRITE STATEMENTS
7-33
7.3.1
Sequential WRITE Statements
7-33
7. 3. 1 . 1
Formatted Sequential WRITE Statement • 7-34
7 .3.1.2
List-Directed Sequential WRITE Statement • 7-35
7 .3.1 .3
Namelist-Directed Sequential W RITE Statement • 7- 3 7
7 .3.1.4
Unformatted Sequential WRITE Statement• 7-39
7 .3.2
Direct Access WRITE Statements
7-39
7 .3.2.1
Formatted Direct Access WRITE Statement• 7-40
7 .3.2.2
Unformatted Direct Access WRITE Statement• 7-40
7 .3.3
Indexed WRITE St atements
7- 4 1
7 .3 .3 . 1
Formatted Indexed WRITE Statement • 7-42
7 .3 .3 .2
Unformatted Indexed WRITE Statement • 7- 43
7 .3.4
Internal WRITE Statement
7-43
7 .3.4. 1
Formatted Internal WRITE Statement• 7-44
7 .3.4 .2
List-Direct ed Internal WRITE Statement • 7- 44

7 .4

REWRITE STATEMEN T
7. 4.1
Formatted REWRI TE Statement
7. 4 .2
Unformatted REWRITE Statement

7- 45
7-46
7-46

7 .5

ACCEPT STATEMENT

7- 47

7.6

TYPE AND PRINT STATEMENTS

7-48

1/0 FORMATTING

8-1

GENERAL RULES FOR WRITING FORMAT STATEMENTS
8.1 .1
Input Rules for FORMAT Statements
8.1 .2
Output Rules for FORMAT Statements

8-2

8-3
8-4

8.2

FORMAT STATEMENT SYNTAX

8-4

8.3

FIELD AND EDIT DESCRIPTORS
Repeat Counts and Group Repeat Counts
8.3.1
Variable Format Expressions
8 .3.2
Blank Control Editing
8.3.3
8.3.3. 1
BN Edit Descriptor• 8-10
8.3.3.2
BZ Edit Descriptor• 8-11
Sign Control Editing
8.3.4
8.3.4. 1
SP Edit Descriptor • 8-11
8.3.4.2
SS Edit Descriptor • 8-11
8.3.4.3
S Edit Descriptor • 8-12
Integer Editing
8.3.5
8.3.5. 1
I Field Descriptor • 8-12
8 .3 .5 .2
0 Field Descri ptor• 8- 14
8 .3 .5 .3
Z Field Descript or • 8- 16
Real Editing
8.3.6
8.3.6. 1
F Field Descriptor• 8-17
8.3.6.2
E Field Descriptor• 8-19
8.3.6.3
D Field Descriptor• 8-21
8.3.6.4
G Field Descriptor • 8-22
8.3.6.5
Complex Data Editing • 8-25
Scale Factor Editing-P Edit Descriptor
8.3.7
Logical Editing-L Edit Descriptor
8.3.8
8.3.9
Character Editing
8.3.9. 1
A Field Descriptor • 8-29
8 .3 .9.2
H Field Descriptor • 8- 32
8.3 .9.3
Character Constants • 8-32
Default Field Descri ptors
8.3 .10
8.3.11
Positional Editing
8.3. 11 . 1 X Edit Descriptor• 8-34
8 .3 . 11 .2 T Edit Descriptor • 8-35
8.3.11.3 TL Edit Descriptor• 8-36
8.3.11.4 TR Edit Descriptor• 8-36

8-7
8-8
P-9

CHAPTER 8

8.1

8-10
8-11

8-12

8-17

8-25
8-28
8-29

8-33

8-34

8.3.12

Additional Editing Operations
8 .3 . 12 . 1
8 .3 . 12 .2
8.3. 12 .3

8-36

Edit Descriptor • 8 - 37
Dollar Sign Descriptor • 8-37
Colon Descriptor • 8-38

8.4

CARRIAGE CONTROL

8-38

8.5

FORMAT SPECIFICATION SEPARATORS

8-39

8.6

EXTERNAL FIELD SEPARATORS

8-40

8.7

RUN-TIME FORMAT

8-41

8.8

FORMAT CONTROL INTERACTION WITH 1/0 LISTS

8-42

AUXILIARY 1/0 STATEMENTS

9-1

OPEN STATEMENT
9.1.1
ACCESS Keyword
9.1.2
ASSOCIATEVARIABLE Keyword
9.1.3
BLANK Keyword
9.1.4
BLOCKSIZE Keyword
9.1 .5
BUFFERCOUNT Keyword
9.1 .6
CARRIAGECONTROL Keyword
9.1 .7
DEFAULTFILE Keyword
9 .1.8
DISPOSE Keyword
9.1.9
ERR Keyword
9.1.10
EXTENDSIZE Keyword
9.1 .11
FILE Keyword
9.1.12
FORM Keyword
9.1.13
INITIALSIZE Keyword
9.1.14
IOSTAT Keyword
9.1.15
KEY Keyword
9.1.16
MAXREC Keyword
9.1.17
NAME Keyword
9.1.18
NOSPANBLOCKS Keyword
9 .1.19
ORGANIZATION Keyword
9 .1.20
READONLY Keyword

9-2
9-8
9-8
9-8
9-9
9-9
9-10
9-10
9-11
9-12
9-12
9-13
9-13
9-1 4
9-14
9- 15
9-1 6
9-17
9-17
9-17
9-18

CHAPTER 9

9.1

9.1.21
9.1 .22
9.1 .23
9.1.24
9.1.25
9.1.26
9.1.27
9. 1.28

xii

RECL Keyword
RECORDSIZ E Keyword
RECORDTYPE Keyword
SHARED Keyword
STATUS Keyword
TYPE Keyword
UNIT Keyword
USEROPEN Keyword

9-18
9- 20
9-20
9-21
9-21
9-22
9-22
9- 23

9.2

CLOSE STATEMENT

9-23

9.3

INQUIRE STATEMENT
ACCESS Specifier
9.3.1
BLANK Specifier
9.3.2
CARRIAGECONTROL Specifier
9.3.3
DIRECT Specifier
9.3.4
9.3.5
ERR Specifier
EXIST Specifier
9.3.6
FORM Specifier
9.3.7
FORMATTED Specifier
9.3.8
9.3.9
IOSTAT Specifier
KEYED Specifier
9 .3.10
NAME Specifier
9.3.11
9.3.12
NAMED Specifier
NEXTREC Specifier
9.3.13
9.3.14
NUMBER Specifier
OPENED Specifier
9.3.15
ORGAN IZATION Specifi er
9 .3.16
9.3.17
RECL Specifier
RECORDTYPE Specif ier
9.3.18
SEQUENTIAL Specifier
9.3.19
UNFORMATTED Specifier
9.3.20

9-24
9-25
9-26
9-26
9-27
9-27
9-27
9-28
9-28
9-28
9- 29
9-29
9-30
9-30
9-30
9-31
9- 31
9-32
9-32
9-33
9-33

9.4

REWIND STATEMENT

9-34

9.5

BACKSPACE STATEMENT

9-35

9.6

ENDFILE STATEMENT

9-35

9.7

DELETE STATEMENT

9-36

9.8

UNLOCK STATEMENT

9- 38

COMPILER DIRECTIVES

10-1

10.1

COMPILER DIRECTIVE SYNTAX RULES

10-1

10.2

PARALLEL DIRECTIVES
CPAR$ CONTEXT_SHARED
10.2 .1
CPAR$ CONTEXT_SHARED_ALL
10.2.2
CPAR$ DO_PARALLEL
10.2.3
CPAR$LOCKON,CPAR$LOCKOFF
10.2.4
10.2.5
CPAR$ PRIVATE
CPAR$ PRIVATE_ALL
10.2.6
10.2.7
CPAR$ SHARED
CPAR$ SHARED_ALL
10.2.8
Parallel Directive Examples
10.2.9

10-2
10-3
10-3
10-4
10-5
10-6
10-7
10- 7
10-8
10-8

10.3

GENERAL DIRECTIVES
10.3.1
CDEC$1DENT
CDEC$ PSECT
10.3 .2
CDEC$ TITLE, CDEC$ SUBTITLE
10.3.3

10- 10
10-10
10- 11
10-13

ADDITIONAL LANGUAGE FEATURES

A-1

A.1

THE ENCODE AND DECODE STATEMENTS

A- 1

A.2

DEFINE FILE STATEMENT

A-3

A.3

FIND STATEMENT

A-5

A .4

PARAMETER STATEMENT

A-6

A.5

OCTAL NOTATION FOR INTEGER CONSTANTS

A- 7

CHAPTER 10

APPENDIX A

xiii

A .6

/ NOF7 7 INTERPRETATION OF THE EXTERNAL STATEM ENT

APPENDIX B CHARACTER SETS

B-1

B.1

FORTRAN CHARACTER SET

B-1

B.2

ASCII CHARACTER SET

B-2

B.3

RADIX- 50 CONSTAN TS A ND CHARACTER SET

B- 4

FORTRAN DATA REPRESENTATION

C-1

C.1

INTEGER*2 REPRESENTATION

C-1

C.2

INTEGER*4 REPRESENTATION

C-2

C.3

LOGICAL*1 (BYTE) REPRESENTATION

C-2

C.4

LOGICAL*2 AND LOGICAL*4 REPRESENTATION

C-2

C.5

FLOATING-POINT REPRESENTATIONS
REAL*4 (f_floating)
C.5.1
REAL*8 (D_floating)
C.5.2
REAL*8 (G _ floating)
C.5 .3
C.5.4
REAL*16 (H_floating)
C.5.5
COMPLEX*8 (f_floating)
C.5.6
COMPLEX*16 (D_floating)
C.5.7
COMPLEX*16 (G_floating)

C-3
C-4
C-5
C-6
C-7
C-8
C-8
C-10

C.6

CHARACTER REPRESENTATION

C-11

C.7

HOLLERITH REPRESENTATION

C-11

APPENDIX C

xiv

A-8

APPENDIX D VAX FORTRAN LANGUAGE SUMMARY

D-1

D.1

EXPRESSION OPERATORS

0-1

D.2

STATEMENTS

0-2

D.3

LIBRARY FUNCTIONS

0-32

D.4

SYSTEM SUBROUTINE SUMMARY
D.4.1
DA TE Subroutine
0 .4 .2
I DA TE Subroutine
D.4.3
ERRSNS Subroutine
D.4.4
EXIT Subroutine
D.4.5
SECNDS Subroutine
D.4.6
TIME Subroutine
D.4 .7
RAN Subroutine

D-45
D- 46
D-47
D-47
D-48
D-48
D- 49
D-50

D.5

BIT FUNCTIONS
D.5.1
Bit Position
D.5 .2
Bit Function Arguments
D.5. 3
MVBITS Subroutine

0-50
D-51
D-51
D- 53

Using Multiple Function Names

6-28

INDEX

EXAMPLES
6-1

FIGURES
1-1

Required Order of Statements and lines

1-3

1-2

FORTRAN Coding Form

1-10

1-3

line Formatting Example

1-12

2-1

Array Storage

2-28

4-1

Equivalence of Substrings

4-18

4-2

Equivalence of Character Arrays

4-19
xv

5-1

Control Transfers and Extended Range

5-10

5-2

Examples of Block IF Constructs

5-20

1-1

Entities Identified by Symbolic Names

2-1
3-1
4-1
4-2

Data Type Storage Requirements

TABLES

xvi

5-1

Nested DO Loops

1-7
2-3
3-3
4-15
4-16
5-7

6-1
6-2
6-3
7-1

Argument List Built- In Functions and Defaults

6- 10

Types of User-Written Subprograms

8-1

FORMAT Code Summary

8-2
8-3

Effect of Data Magnitude on G Format Conversions
Size Limit of Numeric Elements Using the A Field Descriptor

8-4

Default Field Descriptor Values

8-5
9-1
9-2
9-3
10- 1

Carriage Control Characters

6-12
6-27
7-36
8-6
8-23
8-30
8-33
8-39

Common Block Default Attributes and PSECT Modification

B-1

ASCII Character Set

B-3

B-2

RADIX -50 Character Set with Comparative Values

B-4

0-1

Expression Operators

D-1

D-2
D-3

VAX FORTRAN Language

D-3

VAX FORTRAN Intrinsic Functions

D-33

Conversion Rules for Assignment Statements
Equivalence of Array Storage
Equivalence of Arrays with Nonunity Lower Bounds

Summary of Generic Intrinsic Function Names
List-Directed Default Output Formats

OPEN Statement Keyword Values
Record Size (RECL) Limits
Record Size (RECL) Default Values

9-4
9-19
9-19
10- 12

Preface
This manual presents a complete description of the VAX FORTRAN
language for VMS systems. It is designed as a reference manual, not as a
tutorial document.
For detailed instructions on the features of the VAX FORTRAN compiler
and its use, see the VAX FORTRAN User Manual.

Intended Audience
This manual is intended for programmers and students who have a basic
understanding of the FORTRAN language. Readers do not need a detailed
understanding of the VMS operating system, but some familiarity is
helpful. For detailed information about the VMS system, refer to the VMS
documentation set.

Structure of this Document
The documentation for VAX FORTRAN Version 5.0 is a major revision
of the Version 4.0 documentation. The material is reorganized into two
manuals. The VAX FORTRAN Us er Manual describes how to compile, link,
execute, and debug VAX FORTRAN programs on the VMS system. It also
describes special VAX FORTRAN features and system resources of interest
to VAX FORTRAN programmers.

xvii

This manual presents the language-specific information. It is divided into
ten chapters and four appendixes:
•

Chapter 1 discusses VAX FORTRAN's relationship with FORTRAN
standards, the elements of a source program, the character set, general
coding rules, and compiler control statements.

•

Chapter 2 describes the data types, data items, and expressions that
can be used in VAX FORTRAN programs.
Chapter 3 describes the assignment statement, which defines the
values of data items.
Chapter 4 describes specification statements, which are nonexecutable statements. Specification statements allocate and initialize data
items and define various characteristics of symbolic names used in a
program.
Chapter 5 describes control statements, which specify when and
where control transfers from one point in a program to another.
Chapter 6 discusses subprograms (subroutines and functions), both
those written by users and those supplied by VAX FORTRAN.

•
•

•
•
•

•
•
•
•
•
•
•

xviii

Chapter 7 describes 1/0 (input/output) statements, which physically
transfer data, both internally within memory and to and from output
storage devices.
Chapter 8 describes formatting statements, which are used together
with formatted 1/0 statements.
Chapter 9 describes auxiliary 1/0 statements that manage files.
Chapter 10 describes compiler directives, which support directed
decomposition and general-purpose functions.
Appendix A describes some statements and language features that
support programs written in older versions of FORTRAN.
Appendix B summarizes the character sets supported by VAX
FORTRAN.
Appendix C shows how VAX FORTRAN data types are stored in
memory.
Appendix D summarizes VAX FORTRAN features: operators used in
exoressions, statements, intrinsic functions and their arguments, and
system subroutines and bit manipulation functions.

Associated Documents
The following documents contain information directly related to the topic
of this manual:

•

VAX FORTRAN User Manual

•

This manual describes how to perform basic operations using the
VMS system and screen-display editor. The information about the
VMS system and the editor should enable a programmer who is not
acquainted with VMS to begin productive work on it.
The VMS documentation set
This set provides detailed information about features of the VMS
operating system.

Conventions Used in this Document
The following syntactic conventions are used in this manual:
•
•

•
•
•
•

•

Uppercase type is used in text to indicate VMS commands and command options.
Lowercase letters are used in syntax specifications and examples
to indicate variables; anything that is not a variable (for example,
statement names and keywords) appears in uppercase.
Brackets ([]) indicate optional elements within statements.
Braces ({}) are used to enclose lists from which one element is to be
chosen.
Horizontal ellipses (.. .) indicate that the preceding items can be
repeated one or more times .
"Real" (lowercase) is used to refer to the REAL•4 (REAL), REAL•8,
and REAL•16 data types as a group; likewise, "complex" (lowercase)
is used to refer to the COMPLEX•8 (COMPLEX) and COMPLEX•16
(DOUBLE COMPLEX) data types as a group; "logical" (lowercase)
is used to refer to the LOGICAL*2 and LOGICAL•4 data types as a
group; and "integer" (lowercase) is used to refer to the INTEGER•2
and INTEGER•4 data types as a group.
VAX FORTRAN extensions to the FORTRAN-77 standard are printed
in blue ..

xix

In addition, the following notations denote special nonprinting characters:
Tab character
Space character

< TAB >

New and Expanded Language Features
VAX FORTRAN Version 5.0 provides the following new and expanded
language features:
•

Directed decomposition of DO-loops for parallel processing. Parallel
processing is mediated by a group of compiler directives that are
specifically called parallel directives. See Section 10.2.

•

Several general-purpose functions: specifying the identifica tion stnng
in object modules, modifying some common block attributes, and
listing title and subtitle. These functions are mediated by a group of
compiler directives that are specifically called general directives. See
Section 10.3 .

•

Support for descending ISAM (Indexed Sequential Access Mode)
keys:
Expanded syntax for the KEY parameter in the OPEN statement.
See Section 9 .1.15.

•

Additional keywords in the key-field- value specifier in input
/output statements. See Section 7.1.1. 7.
SIZEOF intrinsic function. This new function returns the number of
bytes of storage used in a specified argument. See Table D-3.

•

NWO RKERS intrinsic function. This new function returns the number
of processes executing a routine. See Table D-3 .

•

REWRITE operations on files that are open for direct access. See
Section 7.4.

•

UN LOCK operations of files with sequential organizatio n. See
Section 9.8.

See the VAX FORTRAN User Manual for a description of new compiler
features available in VAX FORTRAN Version 5.0.
xxi

Chapter 1

Introduction to VAX FORTRAN
This chapter discusses VAX FORTRAN's relationship to FORTRAN standards, the elements of a VAX FORTRAN program, the character set, and
general coding rules. It also presents compiler control statements.
VAX FORTRAN is based on the American National Standard
FORTRAN-77 (ANSI X3.9-1978). It includes support for programs that
conform to the previous standard (ANSI X3.9-1966). VAX FORTRAN
also supports programs that conform to the International Standards
Organization FORTRAN standard (ISO 1539-1980 (E)) because the ISO
standard is the same as the ANSI standard.
VAX FORTRAN provides a number of extensions to the ANSI Standard:
•
•

Compiler directives tha t support directed decomposition for parallel
processing
Compiler directives that perform several general-purpose functions

•
•
•
•
•
•
•
•

Relative file organization
Indexed file organization with two-directional keys
Conformance with the VAX procedure-calling standard
Records and structures
DO WHILE statement
Additional data types
Namelist-directed input/output
Hexadecimal constants and field descriptors

•

Symbolic debugging facility

Extensions to the FORTRAN-77 standard appear in blue print in this
manual.
Introduction to VAX FORTRAN

1-1

VAX FORTRAN is also a compatible superset of PDP-11 FORTRAN-77.
This means that existing PDP-11 FORTRAN-77 source programs will
compile properly on the VAX FORTRAN compiler (see the VAX FORTRAN
User Manual).

1.1 Elements of FORTRAN Source Programs
This section provides an overview of the makeup of a FORTRAN source
program. It describes the concept of a program unit and the rules governing the use of statements and symbols within a program unit. It also
describes the use of comments within programs.

1. 1.1

Program Units
A program unit is a sequence of statements that defines a computing
procedure and is terminated by an END statement. A program unit can be
either a main program or a subprogram. An executable program consists
of one main program and, optionally, one or more subprograms.
A subprogram is a program unit that is separate from the main program.
Subprograms are invoked from the main program or another subprogram. There are two types of subprograms: function subprograms and
subroutine subprograms. See Chapter 6 for detailed information on
subprograms.

1. 1.2

Statements
Statements are grouped into two general classes: executable and nonexecutable. Executable statements describe the action of the program.
Nonexecutable statements describe data arrangement and characteristics,
and provide editing and data-conversion information .
Statements are divided into physical sections called lines. A line is a
string of up to 72 characters (optionally, 132; see Section 1.3 .5) . If a
statement is too long to fit on one line, it can continue on one or more
additional lines called continuation lines. A continuation line is identified
by a continuation character in the sixth column of that line. (For further
information on continuation characters, see Section 1.3.4.)

1-2

Introduction to VAX FORTRAN

A statement label can identify a statement so that other statements can
refer to it, either to get information or to transfer control. A statement
label must be an integer, and it must appear in the first five columns of
a statement's initial line. Any statement can have a label. However, you
can only refer to labels on executable statements and FORMAT statements.
Order of Statements in a Program Unit

Figure 1-1 shows the required order of statements in a FORTRAN program unit. In this figure, vertical lines separate statement types that can be
interspersed. For example, you can intersperse DATA statements with executable statements. On the other hand, horizontal lines indicate statement
types that cannot be interspersed. For example, you cannot intersperse
type declaration statements with executable statements.

Figure 1-1:

Required Order of Statements and Lines

OPTI ONS State men t
PROGRAM ,FUNCTION ,SUBROUTINE , or BLOCK DATA Statements
IMPLICIT NON E Statement
IMPLICIT
Statements
Comment
Lines ,
INCLUDE
Stat ements,
and
Genera l
Directives

NAMELI ST
FORMAT
and
ENTRY
Statements

Other
Specification
Statements

DATA
Statements

PARAMETER
Statements

Statement Function
Definitions

Executable
Statements

END Statement
Z K-615-8 2

Introduction to VAX FORTRAN

1-3

The following statements are the general directives that are included in
the category with comment lines and INCLUDE statements in Figure 1-1:
CDEC$IDENT

C DEC$ SUBTITLE

CDEC$ TITLE

CDEC$ PSECT

The following statements are included in the category of executable
statements in Figure 1-1:
ACCEPT

IF (arithmetic, logical, block) and END IF

ASSIGN

INQUIRE

Assignment statements

OPEN

BACKSPACE

PAUSE

CALL

READ

CONTINUE

RETURN

CPAR$ DO_PARALLEL

REWIND

CPAR$ LOCKO FF

REWRITE

CPAR$ LOCKON

STOP

DELETE

TYP E

DO and END DO

UNLOC K

ELSE

WRITE

END
END FILE
FIN D
GO TO (normal, computed, assigned)

1-4

Introduction to VAX FORTRAN

The following statements are included in the category of "other specification statements" in Figure 1-1:
COMMON

EQUIVALENCE

er AR$ CONTEXT_SHARED

EXTERNAL

CPAR$ CONTEXT_SHARED_ALL

INTRINSIC

CPAR$ PRIVAT E

RECORD

CPAR$ PRIVATE _ALL

SAVE

CPAR$ SHARED

Structure declaration s 1

CPAR$ SHARED_ALL

Type declarations

DICTIONARY

VOLATILE

DIMENSION
1

Th e statements STRUCTURE a nd END STRUCTURE, UNION and END UN IO N, and
MAP and END MAP are included in th e "other specifica tion statements" category. They
are used only in structure declaration blocks.

As a VAX FORTRAN extension, DATA statements can be freel y interspersed with PARAMETER statements and other specification statements.

1.1.3

Symbolic Names
Symbolic names identify entities within a FORTRAN program unit. These
entities are listed in Table 1-1.
A symbolic name is a string of letters, digits, and the special characters
dollar sign ( $) and underscore (-)· The first character in a symbolic
name must be a letter. The symbolic name can contain a maximum of
31 characters. (FORTRAN-77 limits the length of a symbolic name to six
characters.)
Examples

The following examples demonstrate valid and invalid symbolic names
and explain why the invalid ones are not valid:

Introduction to VAX FORTRAN

1-5

Valid
NUMBER

FI ND_ IT

x
Invalid

Explanation

Begins with a numeral

B.4

Contains a special character other than _ or $

$FREQ

Begins with $

By convention, symbolic names containing a dollar sign are reserved for
DIGITAL-supplied software components. To avoid name conflicts, do not
define any symbolic names in your program that contain dollar signs.
Symbolic names cannot identify more than one entity in the same program unit-except when they identify common blocks, records, structures,
structure fields, and either arrays or variables. For example, in the following valid statements, X is the name of a common block, a structure, a
structure field, and a variable:
COMMON /X/ I, J
STRUCTURE /X/
I NTEGER X
END STRUCTURE
REAL X

Section 4.15.1 and Section 4.1 5.2 provide more information about structure and field names.
In an executable program having two or more program units, the symbolic
names of the following entities must be unique within the entire program:

•
•
•
•

•
•
•

1-6

Function subprograms
Subroutine subprograms
Common blocks
Main program
Block data subprograms
Function entry points
Subroutine entry points

Introduction to VAX FORTRAN

For example, if your program contains a function named BTU, you cannot use BTU as the symbolic name of any other subprogram, entry, or
common block in the program-even if the name appears in a different
program unit.
Table 1-1 lists those entities that can be given a symbolic name. It also
indicates whether the entities can be given a data type. Sections 2.2.2 .1
and 2.2.2.2 discuss how to specify the data type of a symbolic name.
Table 1-1:

1.1.4

Entities Identified by Symbolic Names

Entity

Typed

Variables

Yes

Arrays

Yes

Structures

Records

Record elements

Yes

Statement functions

Yes

Intrinsic functions

Yes

Function subprograms

Yes

Subroutine subprogram s

Common blocks

Namelist data groups

Main programs

Block data subprograms

Function entry points

Yes

Subroutine entry points

Parameter constants

Yes

Comments
Comments are documentation aids that do not affect program processing
in any way. They can be freely used to describe the actions of a program,
identify program sections and processes, and provide greater ease in
reading a source program listing.

Introduction to VAX FORTRAN

1-7

Three different characters identify comments:
•

The letter C -

except when C begins a compiler directive

•
•

An asterisk ( *)
An exclamation point (!)

When the letter C or an asterisk appears in the first column of a source
line, it identifies the line as a comment. An exclamation point in the fi rst
column, or anywhere in the statement portion of a source line, identifies
the remainder of that line as a commen t.
An all-blank line is also treated as a comment line.
Section 10.2.9 provides an example of when the letter C in column 1
begins a compiler directive instead of a comment.

1.2 Character Set
VAX FORTRAN supports the following character set:
•

All uppercase and lowercase letters (A through Z, a through z)

•

The numerals 0 through 9

•

The following special characters:

Character
t:,.

or < TAB >

1-8

Name

Character

Name

Space or tab

Apostrophe

Equal sign

Quotation mark

Plus sign

Dollar sign

Minus sign

Underscore

Asterisk

Exclam ation point

Slash

Colon

(

Left parenthesis

)

Introduction to VAX FORTRAN

Left angle bracket

Right parenthesis

<
>

Comma

Percen t sign

Period

Ampersand

Righ t angle bracket

You can use the space character to improve the legibility of a FORTRAN
statement. The compiler ignores all spaces in a statement field except
those within a character or Hollerith constant; for example, GO TO and
GOTO are equivalent.
Other printable ASCII characters can appear in a FORTRAN statement
only as part of a character or Hollerith constant (see Appendix B for
a list of printable characters). Any printable character can appear in a
comment. If nonprintable characters appear anywhere in a FORTRAN
source statement, they appear as question marks in the compilation source
listing.
The control character < NEWLINE > ( < LF> or ' A' X) is not supported
in VAX FORTRAN source records. VAX FORTRAN uses < NEWLINE >
to separate successive FORTRAN source lines. If you must manipulate
this character, use the CHAR(lO) fun ction reference, which is allowed in
all compile-time character expressions (see Section 6.3.2.1).
Except in character and Hollerith constants, the compiler makes no
distinction between uppercase and lowercase letters.

1.3 Coding Rules
Coding rules specify the structure of lines in VAX FORTRAN source
code. A line has four fields: the statement label, continuation indicator,
statement, and sequence number. Rules affecting individual fields are
described in Sections 1.3.3 through 1.3.6.
There are two ways to code a line: by fixed format or tab format. The
fixed-format method is convenient when you punch cards or use a coding
form . The tab-format method is convenient when you enter lines at a
terminal with a text editor.

1.3.1

Fixed-Format Lines
As shown in Figure 1-2, a FORTRAN line is divided into fields for
statement labels, continuation indicators, statement text, and sequence
numbers. Each column represents a single character.
To enter an item in a field, enter it in the columns in the coding form, as
follows:

Introduction to VAX FORTRAN

1-9

Figure 1-2:

FORTRAN Coding Form

coou

FORTRAN

OAT(

••Gl

CO O•"" G I Q h•

FORTRAN STATEMENT
I

]) ' ) 6,. 9

1-+-1>-+-+-+

ll)fNTtl l(Afl0N

101 1 1}1)1.al ) l6111l1910J !"J1 7J 1" ])} 61'Jtl9)0)1)2)))41U)6J1)1)9•0• 1 4 ] 4 ) 4••)•6• 1 •1••)0 ) 1 )})))...1)))6)1)1)960616}6)6•U . . 6/ . . 6'f70nn'31•1)7•17'1"t<l

h_H 1 s 1 P1R1qqR,iy.i ,ct,LF=,U,Lf-,T,E ,s, ,PR 1 ME ,NYMB,E,R,s, ,F,R,OM , 1.J.__,.:_T_.,o,.__.""'50"'.......__.--+-..._...-+--._..__._..-+--._.._+-+-+-->-+--+-+-+-1
Q.Q_ 10 l = I I
50 2

>-+-~--<r-1=-J-=+l~->-+---+-+-<--~-~ -- + ~--~>-+---+--+~'"'"~+-+-__._.!J..._._,=.,!.._.-:J._ ~-+-+--~-~ ~ ~-+---+--+-+--+--.+--...+-+-+--+--<-~~ ....-+-<--~-+-+--+--+......-+-->-+--t-+-......-->-+--+-l

IA.=.J.

~ = L I A +-• - ~ -+~~+ --+- · - • - . - +- - + · --- + + + --- --~~-~~~~-+---.~+-+--!
,__~ __,_..,...=
__..l..,_
.L.l. _. ~~-- • - · -- · --~ - ---~~. ----·--+------------~~~~r+-11-------~----l

f--+---~B:..-='-'A._-_.,l' ---+--- · _ ___ ---- ----------- ------------ ----------------+----~--+--4

t------ I F ,{BJ -2.,_..JJJ._,_.___5 _____ _ _____ ____ ~---- -·------ -------->-+---++-+----+-<---i
5

,__

I F _l J -.1.T ~RT J.. FL O+A.:.-:T......_._l.,__1,L.ll_,,_J_..<-+-.=GO_T+0+--=4-~---~~-+-+-<._._.-.-+-+-_.......__--l_-+-+-......._~
_._ _k
~Y~
P~
E ~1~0~
5 __.____,__+ _____. _ _____ _ _ _________~---------------t-+-+--++--+-+-+-l

F-+=on~r<'--1-1'!
,_...,,.u..=.E>---+--+- - - - r-+-+-~ +-·..--+ --+--+--+--+--->

FORMAT J. I 4

+ - -

· -

•

___ · - ·

•

~ + . ~· --------------~~----++----+-+-l

,.._. · - ,._ ___._.._-+- +- --+- +-- -+- +-- +-----+--+---+-----+-·-+ -+-+---+->-+--+-+--+-->-+----~--+-----~>-+-++-+--.--+-+-<-._+-+-.-+-+--+-+---i

' IS _f'..Ll&.'...J.. ••.• ~ .-++ • -+~--·-----· -~-----------~-------+------~

If.ND.

DIGITAL

IEOUIPMIENT CORPORATION

•

MAYNAAO . MASSACHUSIETTS

ZK-613-82

1-10

Field

Column

Statement label

1 through 5

Continuation indicator

Statement

7 through 72 (optionall y, to 132)

Sequence number

73 thro ugh 80

Introduction to VAX FORTRAN

1.3.2

Tab-Format Lines
You can specify the statement label field , the continuation indicator
field , and the statement fi eld using tab formatting. However, you cannot
specify a sequ ence number fie ld using this method of coding. Figure 1-3
illustra tes FORTRAN lines coded using tab formatting and the equivalent
lines with fixed forma tting.
Figure 1-3:

Line Formatting Example
Character-per-Column Format

Format Using T A B Character

C @ID F I RST VALUE
10 @ID I

J + 5• K +

c
1

10 11

s T

A L

0
1

@ID IVA L

1+2

12 13 14 15 16 17 18

* M

19 20

u E
K

ZK-614 -82

The statement label fi eld consists of the characters that you type before
the first tab character. The statement label field cannot have more than
five characters.
After typing the first tab character, you can type eith er the continuation
indicator field or the statement field.
To enter the continuation indicator fiel d, type any nonzero digit after the
first tab . If you enter the continuation indicator field , the statement field
consists of all the characters after the digit to the end of the line.

Introduction to VAX FORTRAN

1-11

To enter the statement field without a continuation indicator field, type the
statement immediately after the first tab . No FORTRAN statement starts
with a digit.
Many text editors and terminals advance the terminal print carriage to
a predefined print position when you press the TAB key. However, this
action is not the VAX FORTRAN compiler's interpretation of the tab
character. The compiler treats the tab character in a statement field the
same way as it treats a space. In the source listing that the compiler
produces, the tab causes the character that follows to be printed at the
next tab stop (located at columns 9, 17, 25, 33, and so on).
NOTE

Do not use tabs when you are using sequence numbers. If you
use tabs to position your sequence numbers, the compiler may
interpret the sequence numbers as part of the statement fields
m your program.

1.3.3

Statement Label Field
Any statement can have a label. A statement label (or statement number)
consists of from one to five decimal digits in the statement label field of a
statement's initial line. Spaces and leading zeros are ignored. An all-zero
statement label is invalid.
Labeled FORMAT and labeled executable statements are the only statements that can be referred to by other statements (see Section 1.1.2).
FORMAT statements are referred to only in the format specifier of an
1/0 statement or in an ASSIGN statement. No two statements within a
program unit can have the same label.
The first column of the label field can contain two special indicators: the
comment indicator and the debugging statement indicator .
The statement label field of a continuation line must be blank-except in
the case of a debugging statement .

1-12

Introduction to VAX FORTRAN

1.3.3.1

Comment Indicator

The letter C (except when beginning a compiler directive); an asterisk
(•); or an exclamation point (!) in column 1 indicates that the line is a
comment. The compiler prints that line in the source program listing and
then ignores it. An all-blank line is also considered to be a comment. The
exclamation point can also be used an ywhere in the statemen t field (except
when used in a Hollerith or character constant) to start an end-of-line
comment.
See Chapter 10 for a description of when the letter C in column 1 begins
a compiler directive instead of a comment.
1.3 .3.2

Debugging Statement Indicator

The letter D in column 1 designates debugging statements. The initial line
of the debugging statement can contain a statement label in the remaining
columns of the label field . If a debugging statement is continued onto
more than one line, every con tinuation line must begin with a D (in
column 1) and a continuation indicator.
The compiler treats debugging statements either as source text to be
compiled or as comments, depending on the setting of the / D_LINES
qualifier on the FORTRAN command. If you specify the /D_ LINES
qualifier, debugging statements are compiled as a part of the source
program. If you do not specify the /D_LINES qualifi er, debugging
statements are treated as comments. See the VAX FORTRA N User Manual
for more information on the /D_LI NES qualifier.

1.3.4 Continuation Indicator Field
A continuation indicator is any character, except a zero or a space, in
column 6 of a FORTRAN line, or any digit, except zero, after the first tab.
The compiler considers the characters after the continuation character to
be the characters following the last character of the previous line, as if
there were no break at that point. If a continuation indicator is a zero or a
space, the compiler considers the line to be an initial line of a FORTRAN
statement.
Comment lines cannot be continued. They can occur between a statement's initial line and its continuation lines, or between successive
continuation lines.

Introduction to VAX FORTRAN

1-13

1.3.5

Statement Field
The text of a FORTRAN statement is placed in the statement field.
Because the compiler ignores the tab character and spaces (except in
character and Hollerith constants), you can space the text in any way
desired for maximum legibility.
By default, the statement field extends to character position 72. If the
default is in effect, any text following position 72 is ignored and no warning message is printed. However, if the /EXTEND_S OURC E qualifier is
specifi ed on the FORTRAN command line, the statement field is extended
to position 132. Any text beyond that position generates a fatal error and
causes immediate termination of the compilation. See the VAX FO RTRAN
User Manual for more information on the /EXTEND_SOU RCE qualifier.

1.3.6

Sequence Number Field
By defa ult, a sequence number or other identifying info rmation can appear in columns 73 through 80 of any line in a FORTRAN program . The
compiler ignores the characters in this field . However, if the /EXTEND_
SOURCE qualifier is specified on the FORTRAN command line, a sequence number fie ld does not exist; the statement field is extended to
position 132. See the VAX FORTRAN Use r Manu al for more information
on the / EXTEND_SOURCE qualifier.

1.4 Compilation Control Statements
In addition to qualifiers on the FORTRAN command line, several statem ents used in the body of a VAX FORTRAN program also influ ence
compilation :

1-14

•

DICTIONARY-extracts records from the Common Data Dictionary
(CDD) and converts them into VAX FORTRAN records.

•
•

INCLUDE-incorporates external source code into programs .
OPTIONS-establishes compiler qualifi ers otherwise specified on
the FORTRAN command line; overrides comma nd line qualifiers if a
conflict occurs between OPTIONS statement quali fi ers and command
line qualifiers.

Introduction to VAX FORTRAN

1.4. 1 DICTIONARY Statement
The DICTIONARY statement incorporates VAX Common Data Dictionary
data definitions into the current VAX FORTRAN source file during compilation. It can occur anywhere in a VAX FORTRAN source file that a
specification statement can occur (see Chapter 4).
The DICTIONARY statement takes the following form:
DICT IONARY 'cdd-path [/ [NO]LIST]'

cdd-path
Is interpreted as the full or relative pathname of a CDD obj ect.

/[NO]LIST
Controls whether the source code representation of the resulting structure declaration is listed in a compilation source listing. The default is
/NOLIST.
Syntax Rules and Behavior

There are two types of CDD pathname: full and relative. Their formation
must conform to the rules for forming VAX COD pathnames.
A full pathname begins with CDD$TOP and specifies the given names
of all its descendants; it is a complete path to the record definition.
Descendant names are separated from each other by a period.
A relative pathname begins with any generation name other than
CDD$TOP and specifies the given names of the descendan ts after that
point. A relative path comes into existence when a default directory is
established with a logical name .
Examples

In the following example, the logical name definition specifies the beginning of the CDD pathname; thus, a relative path name specifies the
remainder of the path to the record definition:
$DEFI NE CDD$DEFAULT CDD$TOP . FOR

The following examples illustrate how a COD pathname beginning with
CDD$TOP overrides the default COD pathname. Consider a record
with the pathname CDD$TOP.SALES.JONES.SALARY. If you defined
CDD$DEFAULT to be CDD$TOP.SALES.JONES, you could then specify a
relative pathname:

Introduction to VAX FORTRAN

1-15

DICTIONARY ' SALARY'

Alternatively, you could specify a full pathname:
DICTIONARY ' CDD$TOP .SALES . JONES.SALARY'

See the VAX Common Data Dictionary Ut ilities Manual for fu rther details.

1.4.2 INCLUDE Statement
The INCLUDE statement directs the compiler to stop reading statements
from the current file and read the statements in the included file or
module . When it reaches the end of the included file or module, the
compiler resumes compilation with th e next statement after the INCLUDE
statement.
The INCLUDE statement takes one of the following forms:
INCLUDE

' [t ext-li b] (modul e- name) [/[NO]LIST]'

INCLUDE

' f il e- spec [/ [NO] LIST] '

text-lib
Is a character string that specifies the text library to be searched. Its form
must be acceptable to the operating system, as described in the VAX
FORTRAN Us er Ma nual.
file -spec
Is a character string that specifies the file to be included. The form of the
file -spec must be acceptable to the operating system, as described in the
VAX FORTRAN User Ma nual.
module-name
Is the name of the text module, located in a text library, that is to be
included. The name of the module must be enclosed in parentheses.
It can be u p to 31 characters long and can contain any alphanumeric
character and the special characters dollar sign ( $ ) and underscore ( _ ).
/[NO]LIS T
Specifies whether the incorporated code is to appear in the compilation source listing. In the listing, a number precedes each incorporated
statement. The number indicates the "include" nesting depth of the code.
The default is /NOLIST.

1-16

Introduction to VAX FORTRAN

Syntax Rules and Behavior

The INCLUDE statement and included fil es have the following rules:
•

An included fil e or module cannot begin with a continuation line.
Each VAX FORTRAN statement must be completely contained w ithin
a single fil e or modul e.

•

An included file or module can contain an INCLUDE statement.

•

The INCLUDE statement can appear an ywhere within a program un it.

•

An y VAX FORTRAN statement can appear in an included fil e or
module. However, the included statements, when combined with
th e other statements in the compilation, must satisfy the statementord ering restrictions described in Figure 1-1.

Example

In the follo wing example, the file COMMON.FOR defines the size of the
blank common block and the size of the arrays X, Y, and Z.
Main Program File

I NCLUDE 'COMMON. FOR'
DI MENSION Z(M)
CALL CUBE
DO 5. I=1 . M
5
Z( I) = X( I)+SQRT( Y(I))

COMMON.FOR File

PARAMETER (M=100)
COMMON X( M).Y (M )

END

SUBROUTI NE CUBE
I NCLUDE ' COMMON. FOR'
DO 10. I=1, M
X(I) = Y(I) **3
RETURN
END

Introduction to VAX FORTRAN

1-17

1.4.3

OPTIONS Statement
The OPTIONS statement overrides or confirms the FORTRAN command
line qualifiers in effect fo r a program unit. It takes the following form:
OPTIO NS qualifier[qualifier . . . ]

qualifier
Is one of th e following:
I [NO] G_FLOATING
I [NO] 14
/ [NO]F77
ALL
[NO] OVERFLOW
/ CHECK = [NO]BOUNDS
[NO] UNDERFLOW
NONE
/N OCHECK
/ [NO]EXTEND_SOURCE

Syntax Rules and Behavior

The OPTIONS statement mus t be the first statement in a program unit,
preceding the PROG RAM, SUBROUTINE, FUNCTION, and BLOCK
DATA statements.
OPTIONS statement qualifiers have the same syn tax and abbreviations
as the FORTRAN command line qualifiers, as described in the VAX
FORTRAN User Manual.
The OPTIONS qualifiers override FORTRAN command line qualifiers, but
only until the end of the program unit in which they are defined. Thus,
an OPTIONS statement must appear in each program unit in which you
wish to override the command line qualifiers.

1-18

Introduction to VAX FORTRAN

Example

In the following example, the check and extend_source options do not
remain in effect across program unit boundaries. The first OPTIONS
statement specifies that only the program unit immediately following it is
to be compiled with full checking and extend_source options, regardless
of the /CHECK and / EXTEND_SOURCE specifications on the FORTRAN
command line. The second OPTIONS statement specifies that only the
program unit following it is to be compiled with the G_floating option.
OPTIO NS /CHECK/EXTEND_SOURCE

END
OPTIO NS /G_FLOATING

Introduction to VAX FORTRAN

1- 19

Chapter 2

Data Types, Data Items, and Expressions
This chapter contains information on the following topics:
•
•
•

Data types-integer, real, complex, logical, character, and BYTE
(Section 2,.1)
Data items-constants, variables, arrays, character substrings, and
records (Section 2.2)
Expressions-arithmetic, character, relational, and logical (Section 2.3)

2. 1 Data Types
Each constant, variable, array, expression, or function reference in a
FORTRAN statement represents typed data. The data type of these items
can be inherent in their constructions, implied by convention, or explicitly
declared.
The following data types are available in VAX FORTRAN:
•
•
•

•

Integer-a whole number.
REAL (REAL*4) -a 'floating point number, that is, a whole number, a
decimal fraction, or a combination of the two.
DOUBLE PRECISION (REAL* 8) -similar to REAL*4, but has more
than twice the degree of accuracy in its representation (the G_floating
implementation also has an extended range).
REAL*l6-similar to REAL*4 but has an extended range and more
than four times the accuracy in its representation .

Data Types, Data Items, and Expressions

2-1

•

COMPLEX (COMPLEX*8)-a pair of REAL•4 values that represent
a complex number; the first value represents the real part of that
number and the second represents the imaginary part.

•
•
•

DOUBLE COMPLEX (COMPLEX*l6)-similar to complex; its real and
imaginary parts are REAL*8 .
Logical-a logical value, .TRUE. or .FALSE .
Character-a string of printable ASCII characters.

•

BYTE- a one-byte storage location that is equivalent to LOGICAL* l.

See Appendix C for descriptions of the VAX hardware representations of
these data types. See Section 4.4 for descriptions of data type declaration
statements.

2.1.1

Storage Requirements
An important attribute of each data type is the amount of memory required to represent a value of that type. Variations on the basic types
affect either the accuracy of the represented value or the allowed range of
values.
ANSI FORTRAN defines a numeric storage unit as the amount of storage
needed to represent a REAL, INTEGER, or LOGICAL value. In VAX
FORTRAN, a numeric storage unit corresponds to four bytes of memory.
REAL*8 and COMPLEX•8 values occupy two of these numeric storage
units, whereas REAL*16 and COMPLEX*16 values occupy four.
ANSI FORTRAN defines a character storage unit as the amount of storage
needed to represent one character value. In VAX FORTRAN, a character
storage unit corresponds to one byte of memory.
VAX FORTRAN provides additional data types for optimum selection of
performance and memory requirements. Table 2-1 lists the data types
available, the names associated with each data type, and the amount of
storage required (in bytes). The form *n appended to a data type name is
called a da ta type length specifier.

2-2

Data Types, Data Items, and Expressions

Table 2-1:
Data Type

Data Type Storage Requirements
Storage Requirements (in bytes)

BYTE

LOGICAL

2 or 4 2

LOGICAL* I

LOG ICAL*2

LOGICAL*4

INTEGER

2 or 42

INTEGER*2

INTEGER*4

REAL

REAL*4

REAL*S

DOUBLE PRECISION

REAL*l6

COMPLEX

COMPLEX*B

COMPLEX*16

DOUBLE COMPLEX

CHARACTER *len

len 3

CHARACTER•(*)
1

BYTE and LOGICAL*l are equivalent. See Section C.3 for information on the range of
values that can be stored in them.
2

Either two or four bytes are allocated, depending on the setting of the [NO]I4 qualifier on
the FORTRAN command line . The default allocation is four bytes .

The value of Jen is the number of characters specified, which can be in the range 1 to
65535 . Passed-length format, *(*), applies to dummy arguments or character functions, and
indicates that the length of the actual argument or function is used (see Section 6.1.1.3
and the VAX FORTRAN User Manual) .

Data Types, Data Items, and Expressions

2-3

2. 1.2

VAX Implementations of REAL*B
The REAL*8 (and thus, COMPLEX*l6) data type has two implementations on a VAX computer: D_floating and G_floating. The G_floating
implementation offers a greater range but is less precise, having a smaller
number of significant digits . D_floating is the default implementation of
REAL*8. You can select G_floating by using the OPTIONS statement or
the /G_FLOATING qualifier on the FORTRAN command line.
Some VAX processors emulate floating-point data types rather than
executing them in hardware or microcoded instruction. Processing time
with software emulation is much slower. Thus, you should be aware
of which data types are emulated on your system and choose them
(especially REAL*8) with this information in mind.
See Sections 2.2.1.2, C.5, C.5.2, and C.5.3 for more detailed information
on the two implementations of the REAL*8 data type.

2.2 Data Items
VAX FORTRAN statements use the following data items:
•
•
•

•
•

2-4

Constants-fixed, self-describing values.
Variables-stored values represented by symbolic names.
Arrays-groups of values that are stored contiguously and can be
referred to individually or collectively. Individual values are called
array elements.
Character substrings-a contiguous segment of a character variable or
character array element.
Records-structured data items consisting of one or more elements
(variables and arrays) or one or more groups of these elements.
Different record elements in the same record can have unlike data
types.

Data Types, Data Items, and Expressions

2.2.1

Constants
A constant is a data item with a fixed value that cannot be changed during
program execution. The value of a constant can be a numeric value, a
logical value, or a character string. There are eight types of constants:

•
•
•
•
•

Integer
Real
Complex
Octal
Hexadecimal

•
•
•

Logical
Character
Hollerith

Octal, hexadecimal, and Hollerith constants have no data type. They
assume a data type that conforms to the context in which they appear (see
Sections 2.2.1.4 and 2.2.1. 7).
All eight types of constants are scalar references in that they resolve into
single, typed data items. (See Section 2.2.6 for more information on scalar
references.)
2.2.1.1

Integer Constants

An integer constant is a whole number with no decimal point. It can have
a leading sign and is interpreted as a decimal number. Integer constants
take the following form :
snn
5

Is an optional sign.

nn
Is a string of decimal digits. Any leading zeros are ignored.

Data Types, Data Items, and Expressions

2-5

Syntax Rules

A minus sign must appear before a negative integer constant, whereas a
plus sign is optional before a positive constant (an unsigned constant is
assumed to be positive).
Except for a leading algebraic sign, an integer constant cannot contain any
character other than the numerals 0 through 9. The value of an integer
constant must be within the range -2147483648 to 2147483647.
Examples

The following examples demonstrate valid and invalid integer constants
and explain why the invalid ones are not valid:
Valid
0

-127
+32123

Invalid

Explanation

99999999999

Number too large

3 . 14

Decimal point not allowed

32,767

Comma not allowed

If the value of the constant is within the range -32768 to 32767, it
represents a 2-byte signed quantity and is treated as an INTEGER*2 data
type . If the value is outside that range, it represents a 4-byte signed
quantity and is treated as an INTEGER•4 data type.

Integer constants can be used to assign signed and unsigned values
to BYTE, LOGICAL• l, LOGICAL*2, and INTEGER*2 data. BYTE and
LOGICAL*l can contain signed integers with a range of -128 to 127 or
unsigned integers with a range of 0 to 255 . LOGICAL*2 and INTEGER•2
can contain signed integers with a range of -32768 to 32767 or unsigned
integers with a range of 0 to 65535 .
The following table illustrates VAX FORTRAN assignments to different
data and lists the integer and hexadecimal values in the data:

2-6

Data Types, Data Items, and Expressions

VAX FORTRAN
Assignment

Integer Value
in the Data

Hexadecimal Value
in the Data

x = -128

- 128

x = 127
x = 255

127

' 7F' X

-1

' FF'X

X = -128

-128

x = 127
x = 255

12 7

' 7F' X

-1

'FF'X

x = -32768

-32768

x = 32767
x = 65535

32767

'7FFF 'X

-1

' FFFF'X

BYTE X
1

80 X

LOGI CA L*l X
1

80 X

LOGICAL*2 X
1

8000 X

I TEGER*2 X

x = -32768
x = 32767

-32768

3 2767

'7FFF'X

x = 65535

-1

'FFFF'X

8000 X

Integer constants can also be specified in octal form, as described in
Sections 2. 2.1.4 and A.5.

Data Types, Data Items, and Expressions

2-7

2.2.1.2

Real Constants
A real constant is a number written with a decimal point, exponent,
or both. The constant can be positive, zero, or negative. It can have
single precision (REAL•4), double precision (REAL•8), or quad precision
(REAL*l6).
REAL*4 (REAL) Constants

A REAL•4 constant can be any one of the following:
•
•

Basic real constant
Basic real constant followed by a decimal exponent

•

Integer constant followed by a decimal exponent

A basic real constant takes one of the following forms:
s . nn
snn . nn
snn .

s
Is an optional sign.

nn
Is a string of decimal digits. A decimal point can appear anywhere in the
string.
A decimal exponent takes the following form:
Esnn

s
Is an optional sign.

nn
Is a string of decimal digits.
Syntax Rules and Behavior

A REAL*4 constant occupies four bytes of VAX storage. It is interpreted
as a real number with a degree of precision that is typically seven decimal
digits (see Sections C.5 and C.5.1.

2-8

Data Types, Data Items, and Expressions

The number of digits is not limited, but typically only the leftmost seven
digits are significant. Leading zeros (zeros to the left of the first nonzero
digit) are ignored in counting the leftmost seven digits. Thus, in the
constant 0.00001234567, all of the nonzero digits, and none of the zeros,
are significant.
The exponent represents a power of 10 by which the preceding real or
integer constant is to be multiplied (for example, 1.0E6 represents the
value 1.0 • 10**6).
A minus sign must appear before a negative REAL•4 constant; a plus
sign is optional before a positive constant. Similarly, a minus sign must
appear between the letter E and a negative exponent, whereas a plus sign
is optional between the letter E and a positive exponent.
A REAL•4 constant can only contain the numerals 0 through 9, algebraic
signs, a decimal point, and the letter E.
When the letter E appears in a REAL•4 constant, an integer constant
exponent field must follow. The exponent field cannot be omitted, but it
can be zero.
The magnitude of a nonzero REAL•4 constant cannot be smaller than
approximately 0.29E-38 or greater than approximately 1.7E38.
Examples

The following examples demonstrate valid and invalid REAL•4 constants
and explain why the invalid ones are not valid:

Data Types, Data Items, and Expressions

2-9

Valid
3 . 14159
621712 .
- . 00127
+5 . 0E3
2E- 3

Invalid

Explanation

1 , 234 , 567 .

Commas not allowed

325E-45

Too small

-47.E47

Too large

100

Decimal point missing - this is a valid integer constant

$25 .00

Special character not allowed

REAL*S (DOUBLE PRECISION) Constants

A REAL*8 constant is a basic real constant or an integer constant followed
by a decimal exponent. Its decimal exponent takes the following form:
Dsnnn
5

Is an optional sign.

nnn
Is a string of decimal digits.
Syntax Rules and Behavior

A REAL*8 constant occupies eight bytes of VAX storage. The number of
digits that precede the exponent is unlimited.
Both D_floating and G_floating implementations of REAL•8 have the
same syntax and storage requirements. However, they differ in the number of significant digits and exponential range. D_floating implementation
typically has 16 (leftmost) significant numbers and a two-digit exponent.
On the other hand, G_floating typically has 15 (leftmost) significant digits
and a three-digit exponent. See Sections C.5, C.5.2, and C.5.3.
D_floating is the default implementation. To select G_floating implementation, you must include the /G_FLOATING qualifier on the FORTRAN
command line.

2-10

Data Types, Data Items, and Expressions

A minus sign must appear before a negative REAL•8 constant; a plus
sign is optional before a positive constant. Similarly, a minus sign must
appear between the letter D and a negative exponent, whereas a plus sign
is optional between the letter D and a positive exponent.
A REAL•8 constant can only contain the numerals 0 through 9, algebraic
signs, a decimal point, and the letter D.
An integer constant exponent field must follow the letter D. The exponent
field cannot be omitted, but it can be zero.
The magnitude of a nonzero REAL•8 constant cannot be less than approximately 0.29D-38 or greater than approximately 1.7D38 for the
D_.floating implementation; nor can it be less than approximately
0.56D-308 or greater than approximately 0.9D308 for the G_.floating
implementation.
Examples

The following examples demonstrate valid and invalid D_.floating and
G_.floating REAL•8 constants and explain why the invalid ones are not
valid:
D_floating REAL•S Constants
Valid
12345678900+5
+2 . 71828182846182000
-72 .50-15
100

Invalid

Explanation

1234567890045

Too large

1234567890 . 00-89

Too small

+2 . 7182812846182

No Dsnnn present;
this is a valid single-precision constant

Data Types, Data Items, and ~xpressions

2-11

G_floating REAL•8 Constants
Valid
123456789 . 00
+2 . 345678901230 - 5
-10+300

Invalid

Explanation

123456789 . 0400

Too large

123456789 . 0-400

Too small

REAL*1 6 Constants

A REAL•16 constant is a basic real constant or an integer constant fol lowed by a decimal exponent. Its decimal exponent takes the following
form:
Qsnnnn

s
Is an optional sign.

nnnn
Is a string of decimal digits.
Syntax Rules and Behavior

A REAL•16 constant occupies 16 bytes of VAX storage. The number of
digits that precede the exponent is unlimited; however, typically only the
leftmost 33 digits are significant (see Sections C.5 and C.5.4).
A minus sign must appear before a negative REAL•16 constant, but a
plus sign is optional before a positive constant. Similarly, a minus sign is
required between the letter Q and a negative exponent, but a plus sign is
optional between the letter Q and a positive exponent.
A REAL•16 constant can only contain the numerals 0 through 9, algebraic
signs, a decimal point, and the letter Q.
An integer constant exponent field must follow the letter Q. The exponent
field cannot be omitted, but it can be zero.
The magnitude of a nonzero REAL• 16 constant cannot be less than
approximately 0.84Q-4932 or greater than approxim ately 0.59Q4932.

2-12

Data Types, Data Items, and Expressions

Examples
The following examples demonstrate valid and invalid REAL* 16 constants
and explain why the invalid ones are not valid:
Valid
12345678904000
- 1 . 23Q -4 00
+2 . 72QO

2.2.1.3

Invalid

Explanation

1 . Q5000

Too large

1. Q-5000

Too small

Complex Constants
A complex constant is a pair of real or integer constants. The two constants are separated by a comma and enclosed in parentheses. The first
constant represents the real part of that number; the second constant
represents the imaginary part.
VAX FORTRAN supports COMPLEX*8 and COMPLEX*l 6 complex
constants.

COMPLEX*S (COMPLEX) Constants
A COMPLEX*8 constant is a pair of integer or REAL*4 constants that
represents a complex number. It takes the following form:
(c. c)

c
Is an integer or REAL*4 constant.
The parentheses and comma are required parts of the constant. (See
Section 2.2.1.2 for the rules for forming REAL*4 constants.)
A COMPLEX*8 constant occupies eight bytes of VAX storage and is
interpreted as a complex number (see Sections C.5 and C.5.5).

Data Types, Data Items, and Expressions

2-13

Examples
The following examples demonstrate valid and invalid COMPLEX•8
constants and explain why the invalid ones are not valid:
Valid
(1 . 7039 ,- 1 . 70391)
(+12739E3,0 . )
(1 , 2)

Invalid

Explanation

( 1 . 23.)

Missing second REAL constant

( 1 . 0. 1. OQO)

REAL*l6 constant not allowed

COMPLEX*1 6 (DOUBLE COMPLEX) Constants
A COMPLEX•16 constant is a pair of constants that represents a complex
number. One constant must be REAL•8; the other must be an integer,
REAL•4, or REAL•8. The two constants are separated by a comma and
enclosed in parentheses; the first constant represents the real part of
the complex number, the second the imaginary part. There are two
implementations of CO MPLEX• 16, corresponding to the D_floating and
G_floating implementations of REAL•8 .
A COMPLEX•16 constant takes the following form:
(c. c)

c
Is an integer, a REAL•4, or a REAL• 8 constant. (One of the pair must be a
REAL•8 constant.)
A COMPLEX•16 constant occupies 16 bytes of VAX storage and is interpreted as a complex number (see Sections C.5, C.5 .6, and C.5.7).
The parentheses and the comma are required parts of the constant.
Syntax rules for REAL•8 constants also apply to the REAL•8 portion of
COMPLEX•16 constants.

2-14 Data Types, Data Items, and Expressions

Exa mples

The following examples demonstrate valid and invalid COMPLEX*16
constants and explain why the invalid examples are not valid:
Valid
(1 . 7039D0. - 1 . 7039DO)
(+12739D3 ,0 .DO)

2.2. 1 .4

Invalid

Explanation

(1 , 2300 )

Second con stant missing

(0 .8Q0,0 . 4QO)

REAL*16 constants not allowed

(1 . 0D300,-1 .0D300)

Both cons tants out of range for D_floating imple men tation of REAL*8; they are valid for G_floating
implementation of REAL* 8

Octal and Hexad e cimal Constants

Octal and hexadecimal constants are alternative ways to represent numeric
constants. They can appear wherever numeric constants are allowed.
An octal constant is a string of octal digits enclosed by apostrophes and
followed by the letter 0 . It takes the following form:
'c1c2c3 .. . cn'O

en
Is a digit with a range of 0 to 7.
A hexadecimal constant is a string of digits enclosed by apostrophes and
followed by the alphabetic character X. It takes the follo wing form:
'c1c2c3 . . . cn'X

en
Is a digit in the range of 0 to 9, or an uppercase or lowercase letter in the
range of A to F.
Leading zeros are ignored in octal and hexadecimal constants. You can
specify up to 128 bits (43 octal digits, 32 hexadecimal digits).

Data Types, Data Items, and Expressions

2- 15

Examples

fhe following examples demonstrate valid and invalid octal and hexadecimal constants and explain why the invalid ones are not valid:
Octal Constants
Valid
'07737 ' 0
'1'0

Invalid

Explanation

'7782'0

The character 8 is invalid

7772'0

No initial apostrophe

'0737'

No 0 after second apostrophe

Hexadecimal Constants
Valid
'AF9730'X
'FFABC 'X

Invalid

Explanation

'999. Ix

Invalid character

'F9X

No apostrophe before X

Data-Typing Octal and Hexadecimal Constants

Octal and hexadecimal constants have no data type until they are used.
When used, they assume a data type based on their use .
When the constant is used with a binary operator, including the assignment operator, the data type of the constant is the data type of the other
operand. For example:

2-16

Data Types, Data Items, and Expressions

Data Type of
Constant

Length of
Constant
(in bytes)

RAPHA = '99AF2 ' X

REAL*4

JCOUNT = !COUNT + ' 777 '0

INTE GER*2

DOUBLE= 'FFF99A'X

RE AL*8

IF (N . EQ. ' 123 ' 0) GO TO 10

INTEGER*4

Statem en t
I NTEGER*2 !COUNT
REAL*B DOUBLE

When a specific data type (generally integer) is required, that type is
assumed fo r the constant. For example:

Statement

Data Type of
Constant

Length of
Constant
(in b ytes)

Y(IX ) = Y( '15' 0) + 3 .

INTEGER*4

When the constant is used as an actual argument, no data type is assumed .
However, a length of fou r bytes is always used. For example:

Statemen t

Data Type of
Constant

Length of
Constant
(in bytes)

CALL APAC('34BC2'X)

None

Wh en the con stant is used in any oth er context, an INTEGER*4 data
type is assumed (or an INTEGER*2 data type if /NOI4 is in effect) . For
example:

Statement

Data Type of
Constant

Length of
Constant
(in bytes)

IF ( IAF77 IX ) 1 ,2, 3

INTEGER*4

I = '7777' 0 - ' A39 'X

INTEGER*4

J = . NOT. I73777 I0

INTEGER•4

An octal or hexadecimal constant specifi es up to 16 bytes of data. When
the data type implies that the length of the constant is more than the
Data Types, Data Items, and Expressions

2-17

number of digits specified, the leftmost digits have a value of zero. When
the data type implies that the length of the constant is less than the
number of digits specified, the constant is truncated on the left. An error
results if any nonzero digits are truncated. Table 2-1 lists the number of
bytes that each data type requires.
2.2.1.5

Logical Constants

A logical constant specifies a logical value, true or false. Thus, only the
following two logical constants are possible:
. TRUE .

. FALSE .

Both delimiting periods are required.
2.2.1.6

Character Constants

A character constant is a string of printable ASCII characters enclosed by
apostrophes. It takes the following form :
'c 1c2c3 . .. en'

en
Is a printable ASCII character.
Syntax Rules and Behavior
Both delimiting apostrophes are required.
The value of a character constant is the string of characters between
the delimiting apostrophes . The value does not include the delimiting
apostrophes, but does include all spaces or tabs within the apostrophes.
Within a character constant, the apostrophe character is represented by
two consecutive apostrophes with no space or other character between
them.
The length of the character constant is the number of characters between
the apostrophes, except that two consecutive apostrophes represent a
single apostrophe. The length of a character constant must be in the range
of 1 to 2000.
If a character constant appears in a numeric context (for example, as the
expression on the right side of an arithmetic assignment statement), it is
considered a Hollerith constant (see Section 2.2.1. 7).
2-18

Data Types, Data Items, and Expressions

Examples

The following examples demonstrate valid and invalid character constants
and explain why the invalid ones are not valid:
Valid
'WHAT?'
'TODAY' 'S DATE IS : I
I

HE SAID. "HELLO" I

Invalid

Explanation

HEADINGS

No trailing apostrophe

Character constant must contain at least one
character

"NOW/OR NEVER"

2.2 . 1. 7

Quotation marks cannot take the place of apostrophes

Hollerith Constants

A Hollerith constant is a string of printable ASCII characters preceded by
a character count and the letter H. It takes the following form:
nH c 1c2c3 . .. en

n
Is an unsigned, nonzero integer constant stating the number of characters
in the string (including spaces and tabs).

en
Is a printable ASCII character.
Hollerith constants are strings of 1 to 2000 characters. They are stored as
byte strings, one character per byte.
Examples

The following examples demonstrate valid and invalid hollerith constants
and explain wh y the invalid ones are not valid:

Data Types, Data Items, and Expressions 2-19

Valid
16HTODAY' S DATE IS:
1HB

Invalid

Explanation

3HABCD

Wrong number of ch aracters

Hollerith constants m ust contain at least one
ch aracter

Data-Typing Hollerith Constants

Hollerith constants have no data type . They assume a numeric data
type based on the way they are used. Hollerith constants cannot assume
a character data type and cannot be used where a character value is
expected.
When the constant is used with a binary operator, including the assign ment operator, the data type of the constant is the data type of the other
operand. For example:

Data Type of
Constant

Length of
Constant
(in bytes)

RALPHA = 4HABCD

REAL* 4

JCOUNT = ! COUNT + 2HXY

INTEGER*2

DOUBLE = 8HABCDEFGH

REAL*8

IF (N . EQ . 1HZ ) GO TO 10

INTEGER*4

Statem en t
INTEGER*2 ! COUNT
REAL* 8 DOUBLP:

When a specific data type is required (generally integer), that type is
assumed for the constant. For example:

2-20

Data Types, Data Items, and Expressions

Statement
Y (I X)

= Y(lHA ) + 3 .

Data Type of
Constant

Length of
Constan t
(in bytes)

INTEGER*4

When the constant is used as an actual argument, no data type is assumed.

Statement

Data Type of
Constant

Length of
Constant
(in bytes)

CALL APAC (9HABCDEFGH I)

None

When the constant is used in any other context, an INTEGER* 4 data
type is assumed (or an INTEGER*2 data type if /NOI4 is in effect). For
example:

Statement

Data Type of
Constant

Length of
Constant
(in bytes)

IF (2HAB) 1,2 ,3

INTEGER*4

I = 1HC - 1HA

INTEGER*4

J = . NOT. 1HB

1NTEGE R*4

When the length of the constant is less than the length implied by the
data type, spaces are appended to the constant on the right. When the
length of the constant is greater than the length implied by the data type,
the constant is truncated on the right. An error results if any characters
other than space characters are truncated.
Table 2-1 (in Section 2.1.1) lists the number of characters required for
each data type . Each character occupies one b yte of storage.

Data Types, Data Items, and Expressions

2-21

2.2.2

Variables
A variable is represented by a symbolic name associated with a storage
location. The value of the variable is the value currently stored in that
location; you can change its value at any point in a program by assigning
a new value to it. (See Section 1.1.3 for the form of a symbolic name.)
Variables are classified by data type, just as constants are. The data type
of a variable indicates the type of data it contains, its precision, and its
storage requirements. When data of any type is assigned to a variable, it
is converted, if necessary, to the data type of the variable.
The following statements and rules establish the data type of a variable:
•
•
•

Type declaration statements
IMPLICIT statements
Predefined typing rules

All types of variables are scalar references in that they resolve into single,
typed data items. (Section 2.2.6 discusses scalar references.)
Associating Variables

Two or more variables are associated with each other when each is
associated with the same storage location. They are partially associated
when part (but not all) of the storage associated with one variable is the
same as part or all of the storage associated with another variable.
Association and partial association occur when you use COMMON or
EQUIVALENCE statements; MAP declarations (within structure declaration blocks) or actual arguments and dummy arguments in subprogram
references.
If variables of different data types are associated (or partially associated)

with the same storage location, and the value of one variable is defined
(for example, by assignment), the value of the other variable becomes
undefined. This occurs because a variable is defined only if the storage
associated with it contains data of the same type as the name.
A variable can be defined before program execution by a DATA statement
or during execution by an assignment or input statement.

2-22

Data Types, Data Items, and Expressions

2.2.2.1

Data Type by Specification

Data type declaration statements explicitly specify the data type of variables (see Section 4.4). For example, the following statements associate
VARl with an 8-byte complex-data storage location, and VAR2 with an
8-byte double-precision storage location:
COMPLEX VAR1
DOUBLE PRECISION VAR2

You can explicitly specify the data type of a variable only once.
An explicit data type specification takes precedence over the type specified
by an IMPLICIT statement. The data type specified by an IMPLICIT
statement associates with a variable only when an explicit specification is
absent. Thus, in the absence of an explicit specification, any variable with
a name that begins with the letter in the range specified in the IMPLICIT
statement becomes the data type of the variable.
Character type declaration statements (see Sections 4.4 and 4.4.2) specify
that given variables represent character values with the length specified.
For example, the following statements associate the variable names
INLINE, NAME, and NUMBER with storage locations containing character
data of lengths 72, 12, and 9, respectively:
CHARACTER*72 INLINE
CHARACTER NAME*12, NUMBER*9

In single subprograms, passed-length character arguments process character strings with different lengths. The passed-length character argument
has a length specification of asterisk (*); for example:
CHARACTER*(*) CHARDUMMY

The passed-length character argument assumes the length of the actual
argument. (See Section 6.1.1.3 and the VAX FORTRAN User Manual.)

Data Types, Data Items, and Expressions

2-23

2.2.2.2

Data Type by Implication

In the absence of either IMPLICIT statements or explicit data type declarations, all variables with names beginning with I, J, K, L, M, or N are
assumed to be integer variables. Variables with names beginning with any
other letter are assumed to be REAL*4 variables. For example:

2.2.3

Real Variables

Integer Variables

ALPHA

JCOUNT

BETA

ITEM

TOTAL

NTOTAL

Arrays
An array is a group of contiguous storage locations associated with a
single symbolic name, the array name. The individual storage locations,
array elements, are referenced by a subscript appended to the array name.
An array can have from one to seven dimensions. For example, a column
of figures is a one-dimensional array. A table with more than one column
of figures is a two-dimensional array. To refer to a specific value in this
array, you must specify both its row and column numbers. A table of
figures that covers several pages is a three-dimensional array. To locate a
value in this array, you must specify the page, row, and column numbers.
The following VAX FORTRAN statements establish arrays:
•

Data type declaration (see Section 4.4)

•

DIMENSION (see Section 4.5)

•

COMMON (see Section 4.2)

These statements contain array declarators that define the name of the
array, the number of dimensions in the array, and the number of elements
in each dimension.
Associating Arrays

Two or more arrays are associated when each one is associated with the
same storage location. They are partially associated when part of the
storage associated with one array is the same as part or all of the storage
associated with another array.

2-24 Data Types, Data Items, and Expressions

Association and partial association occur when you use COMMON or
EQUIVALENCE statements; MAP declarations (within structure declaration blocks); or actual arguments and dummy arguments in subprogram
references.
If arrays with different data types are associated (or partially associated)
with the same storage location, and the value of one array is defined (for
example, by assignment), the value of the other array becomes undefined.
This happens because an element of an array is considered defined only if
the storage associated with it contains data of the same type as the array
name (see Section 2.2.3.3).

The DATA statement defines an array element or an entire array before
program execution. During program execution, array elements are defined
by an assignment or input statement, and entire arrays are defined by
input statements.
2.2.3.1

Array Declarators

An array declarator specifies the symbolic name that identifies an array
within a program unit and indicates the properties of that array. It takes
the following form:
a(d[ , d]

.. . )

a
Is the symbolic name of the array. (Section 1.1.3 gives the form of a
symbolic name.)

d
Is a dimension declarator that can specify both a lower bound and an
upper bound:
[dl : ]du

Is the lower bound of the dimension.

du
Is the upper bound of the dimension. An asterisk (*) can be used as an
upper bound, but only for the last dimension of a dummy argument.
An asterisk marks the declarator as an assumed-size array declarator
(see Section 6.1.1.2).
The number of dimension declarators indicates the number of dimensions
in the array. The number of dimensions can range from one to seven.
Data Types, Data Items, and Expressions

2-25

The value of the lower-bound dimension declarator can be negative, zero,
or positive. The value of the upper-bound dimension declarator must be
greater than or equal to that of the corresponding lower-bound dimension
declarator. The number of elements in the dimension is du - dl + 1. If
a lower bound is not specified, it is assumed to be one, and the value
of the upper bound specifies the number of elements in that dimension.
For example, a dimension declarator of 50 indicates that the dimension
contains 50 elements.
Each dimension bound is an integer arithmetic expression in which each
operand is a constant, a dummy argument, or a variable in a common
block. The expression is converted to an integer if necessary.
The type of a variable used in a bound expression cannot be changed by a
later type declaration.
NOTE

Do not use array references and references to user-defined
functions in dimension bounds expressions.
Dimension bounds that are not constant expressions can be used in a
subprogram to define adjustable arrays. You can use adjustable arrays
within a single subprogram to process arrays with different dimension
bounds by specifying the array name as a subprogram argument, and by
either specifying the bounds as subprogram arguments or by placing the
bounds in a common block. (See Section 6.1.1.1 for more information on
adjustable arrays.) Dimension bounds that are not constant expressions
are not permitted in a main program.
The number of elements in an array is equal to the product of the number
of elements in each dimension.
An array name can appear in only one array declarator within a program
unit.

2-26 Data Types, Data Items, and Expressions

2.2.3.2

Array Subscripts

A subscript qualifies an array name. A subscript is a list of expressions,
called subscript expressions, enclosed in parentheses, that determine which
element in the array is referred to. The subscript is appended to the array
name it qualifies.
Subscript array references are scalar references in that they resolve into
single, typed data items. (Section 2.2.6 describes this terminology.)
A subscript takes the following form:
(s[ . s] . . . )

s
Is a subscript expression.
A subscripted array reference must contain one subscript expression for
each dimension defined for that array (one for each dimension declarator).
Each subscript can be any valid arithmetic expression. However, non integer subscript expressions are converted to integers before use (any
fra ctional parts are truncated).
2.2.3.3

Arrangement of Array Elements in Storage

As discussed earlier in this section, you can think of the dimensions of an
array as pages, rows, and columns. However, FORTRAN actually stores
arrays in memory as a linear sequence of values. A one-dimensional array
is stored with its first element in the first storage location and its last
element in the last storage location of the sequence. A multidimensional
array is stored so that the leftmost subscripts vary most rapidly. This is
called the "order of subscript progression." For example, Figure 2-1 shows
array storage in one, two, and three dimensions.

Data Types, Data Items, and Expressions

2-27

Figure 2-1:

Array Storage

One-Dimensional Array BRC (6)

BRC(2)

BRC(3)

BRC(4)

BRC(5)

BRC(6)

- - - - - - - - M e m o r y Positions

Two-Dimensional Array BAN (3.4)

BAN(1 ,1)

BAN(1,2)

BAN(1,3)

10 BAN(1,4)

BAN(2 , 1)

BAN(2 ,2)

BAN(2,3)

11 t BAN(2 ,4)

BAN(3 , 1)

BAN(3 ,2)

BAN(3 ,3)

12 BAN(3,4)

Memory Pos1t1ons

Three- Dimensional Array BOS (3 ,3,3)

BOS(1, 1,3)

BOS(1,2,3)

BOS(1,3,3)

BOS(2,1,3)

BOS(2,2,3)

BOS(2,3,3)

BOS(3,3,3)

BOS(1, 1,2)

BOS(1,2 ,2)

16 BOS(1,3,2)

BOS(2,1 ,2)

BOS(2,2,2)

17 BOS(2,3,2)

BOS(1, 1,1)

BOS(1,2 ,1)

BOS(1 ,3,1)

BOS(2,1 ,1)

BOS(2 ,2, 1)

BOS(2 ,3,1)

BOS(3 , 1,1 )'

808(3,2,1)

BOS(3 ,3,1)

18 BOS(3,3,2)

Memory Pos1t1ons
ZK-616 -82

2-28 Data Types, Data Items, and Expressions

2.2.3.4

Data Type of an Array

The data type of an array is specified in the same way as the data type of
a variable-implicitly by the initial letter of the name, or explicitly by a
data type declaration statement (see Sections 2.2.2.1 and 2.2.2.2).
All the values in an array have the same data type. Any value assigned
to an array element is converted to the data type of the array. If an array
is named in a DOUBLE PRECISION statement, for example, the compiler
allocates an 8-byte storage location for each element of the array. When
a value of any type is assigned to any element of that array, the value is
converted to double precision.
2.2.3.5

Array References without Subscripts

In the following statements, you can specify an array name without a
subscript to indicate that the entire array is to be used (or defined):

•
•
•
•

•
•
•

COMMON
DATA
EQUIVALENCE
NAME LIST
SAVE
I/O
Data type declaration

You can also use unsubscripted array names as dummy arguments in
FUNCTION, SUBROUTINE, and ENTRY statements, and as actual arguments in references to external procedures. Using unsubscripted array
names is not permitted in all other types of statements.
2.2.3.6

Adjustable Arrays

Adjustable arrays allow subprograms to manipulate arrays of variable
dimensions. To use an adjustable array in a subprogram, you specify the
array bounds, as well as the array name, as subprogram arguments. The
bounds may also be given in a common block. See Section 6.1.1.1 for
more information.

Data Types, Data Items, and Expressions

2-29

2.2.3. 7

Assumed-Size Arrays
Assumed-size arrays are similar to adjustable arrays . With assumed-size
arrays, however, an asterisk is used to specify the upper bound of the last
dimension. Section 6.1.1.2 describes the rules governing the dimensions
that are assumed.

2.2.4

Character Substrings
A character substring is a contiguous segment of a character variable or
character array element. It takes one of the following forms :
v( [e1] : [e2])
a(s[ , s] . .. ) ([e1] : [e2])

v
Is a character variable name.

a
Is a character array name.

s
Is a subscript expression.
e1
Is a numeric expression that specifies the leftmost character position of the
substring.

e2
Is a numeric expression that specifies the rightmost character position of
the substring.
Character positions within a character variable or array element are numbered from left to right, beginning at one. For example, LABEL(2:7) specifies the substring beginning with the second character position and ending
with the seventh character position of the character variable LABEL. If
the CHARACTER•8 variable LABEL has a value of 'XVERSUSY', then the
substring LABEL(2:7) has a value of VERSUS.
If the value of the numeric expression e 1 or e2 is not of type integer, it is
converted to an integer value by truncating any fractional part before use.

2-30

Data Types, Data Items, and Expressions

The values of the numeric expressions e 1 and e2 must meet the following
conditions:
(1 .LE . el) .AND . (el . LE . e2) .AND . (e2 . LE . len)

/en

Is the length of the character variable or array element.
If el is omitted, FORTRAN assumes that el equals one. If e2 is omitted,
FORTRAN assumes that e2 equals len. For example, NAMES(l,3)(:7)
specifies the substring starting with the first character position and ending with the seventh character position of the character array element
NAMES(l,3).

2.2.5

Records
A record is an aggregate entity containing one or more elements. (Record
elements are also called fields or components.) You can use records when
you need to declare and operate on multifield data structures in your VAX
FORTRAN programs. You can also access records in the VAX Common
Data Dictionary (CDD) and use them in your programs.

NOTE
Do not confuse a VAX FORTRAN record with an RMS I/O
record . VAX FORTRAN records are named data entities with
one or more fields that you create in your program.
A record is similar to an array in that they both contain one or more
elements. However, a record differs from an array in the following
respects:
•

Unlike arrays, which are defined by a single declaration statement,
creating a record is a two-step process:
1. Defining the form of the record with a multistatement structure

declaration.
2. Declaring the record as an entity with a symbolic name, thus
establishing its structure in memory . More than one RECORD
statement can refer to a given structure .
•

Unlike arrays, whose data elements must ha ve the same data type,
records can have fields with different data types. Because records have
heterogeneous data elements, they are not typed as arrays are. Record
fields can be operated on individually or collectively.

Data Types, Data Items, and Expressions

2-31

•

Unlike array elements, each element of a record can be named.
References to a record element consist of both the name of the record
containing the element and the name of the desired element.

Structure Declaration Blocks

A structure declaration block is a named group of statements that define
the form of a record.
To establish a structure declaration in memory, its name must be specified
in a RECORD statement.
A structure declaration block includes one or more of the following items:

•

Data Typ e Declarations (variables or arrays): Data type declarations
in structure declarations have the form of normal VAX FORTRAN
data type declarations. Data items with different types can be freely
intermixed within a structure declaration. For example, INTEGER and
LOGICAL data items can be declared in the same structure.
Substructure Declarations: Substructures can be established with a
structure by using either a nested structure declaration or a RECORD
statement.
Structure declarations can be nested within structure declarations.
A nested structure declaration must have one or more field names
specified on its STRUCTURE statement. A nested structure
declaration can optionally be given a structure name for later
reference by a RECORD statement.
The fields in another, previously declared, structure declaration
can be incorporated in a structure by including, within a structure
declaration, a RECORD statement naming the other structure.
This feature enables you to create a structure declaration and
then include it, as necessary, as a substructure declaration within
other structure declarations. Depending on the needs of an
application, this can have advantages over the use of nested
structure declarations, which are individually coded within a
containing, outer structure.

•

Mapped Field Declarations: Mapped field declarations are made up of
one or more typed data declarations, substructure declarations (nested
structure declarations and RECORD statements), or other mapped field
declarations.

2-32

Data Types, Data Items, and Expressions

•

Mapped fi eld declarations are defined by a block of statem en ts called
a union declara tion. Unlike typed data declarations, all mapped field
declara tions that are made within a single union declaration share
a common location within the containing structure. This capability
is similar to using EQUIVALENCE statements to give names to
variables and arra ys. In other languages, it is called a "varian t record"
capability.
Unn amed Fields : Unnamed fields can be declared in a structure by
specifying %FILL in place of an actual field n ame . This m echanism can be used to generate space in a record for purposes such as
alignment.
Unnamed fields cannot be initialized. For example, the following fi eld
declaration is invalid and generates an error message:
I NTEGER*4 %FILL /1980 /

For a detailed description of the syntax and use of RECORD statements
and stru cture declarations, see Sections 4.13 and 4.1 5.
2.2.5.1

Arrangement of Records in Storage

FORTRAN stores a record in memory as a linear sequence of values, with
the record 's first element in the first storage location and its last element
in the last storage location . No gaps are left between elements. A record
array is stored in a similar fashion, with no gaps between array elements.
Examples

The following examples contain structure declaration blocks, RECORD
statements, and diagram s of the resulting records as they are stored in
memory .
The firs t example shows a basic structure declaration block and RECORD
statement:

Source Code
STRUCTURE /STRA/
CHARACTER*l CHR
I NTEGER*4 I NT
END STRUCTURE

RECORD / STRA/ REC.AREC (2)

Data Types, Data Items, and Expressions

2-33

Memory Diagram

5 (byte off set)

REC .INT

REC .CHA

Record REC
Z K - 1844 - 84

1.....A_R
_E_c_(,_
)._c H
_ R_l.___ ___

A_RE-~i

1O (byte offset)

ARECl~~l-IN_r

1) INT

--JI

___

Reco rd array AREC
ZK - 1843-84

2-34

Data Types, Data Items, and Expressions

The next example includes a substructure:

Source Code
STRUCTURE / STRB/
REAL*8 FLT
RECORD /STRA/ STR (2)
END STRUCTURE

RECORD / STRB/ NRD

Memory Diagram
0

8
NRD FLT

NRD STR (l) CHR

NRD ST:,_
11_
) IN
_ r_

Substructure
STRA (STRi 1))

18 (byte oHset)

~N_R_o._sr_R_12_i.c_H_R~--NR_o_.s-T~
-i
Substructure
STRA (S TR(2) )

Record NRD
ZK- 184 2 -84

The next example shows how unions cause the storage of the associated
mapped fields to be overlaid:

Source Code
STRUCTURE /STR/
INTEGER*4 TAG
UNION
MAP
REAL*4 FLT
CHARACTER*2 CHR
END MAP
MAP
INTEGER*2 I NT
END MAP
END UNION
LOGICAL*1 LOG
END STRUCTURE

Data Types, Data Items, and Expressions

2-35

Memory Diagram
6

(byte off set )

l
FLT

CHR

TAG

LOG
IN T

(un use d )

A rea fo r mapped fi e lds

ZK - 184 5- 84

2.2.5 .2

References to Record Fields

References to record fiel ds m ust correspond to the kind of fi eld being
referenced. Aggregate field references refer to composite structures (and
substructures). Scalar field references refer to singular data items, such as
variables.
An operation on a record can involve one or m ore fi elds.
Record field references take one of the following fo rm s:

Aggregate Field Reference
record-nam e [ . aggregate - field- name]

Scalar Field Reference
record- name [ . aggregate-f ie l d- name ] .... s calar- fie l d- name

record-name
Is the n ame used in a RECORD statement to iden tify a record . See
Section 4.13 fo r a description of the RECORD statement.
aggregate -field-name
Is the name of a field that is a substructure (a record or a nested structure
declaration) within the record structure identified by the record name .

See Section 4.15 for a descrip tion of how fields are specified within
structure declarations .
scalar- field- name
Is the name of a typed data item defined within a structure declaration .
2-36

Data Types, Data Items, and Expressions

Scalar field references are scalar references in that they resolve into single,
typed data items . Conversely, aggregate field references are aggregate
refe rences in that they resolve into references to structured data items:
records and nested structure declarations. Aggregate field references
are the only references that fall into the aggregate reference category.
(Section 2.2 .6 discusses this terminology.)
Syntax Ru les and Behavior

Records and record fields cannot be used in EQUIVALENCE statements.
However, you can make fields of record structures equivalent to themselves by using the UNION and MAP statements in a structure declaration
block (see Section 4.15 .1).
A scalar field reference consists of the name of a record (as specified in
a RECORD statement) and zero or more levels of aggregate field names
followe d by the name of a scalar field. A scalar field reference refers to
a single, typed data item and can be treated like a normal reference to a
FORTRAN variable or array element.
Scalar field references can be used in statement functions and in executable statements. However, they cannot be used in COMMON, SAVE,
NAMELIST, or EQUIVALENCE statements, or as the control variable in
an indexed DO-loop.
Type conversion rules for scalar field references are the same as those for
variables and array elements.
An aggregate field reference consists of the name of a record (as specified
in a RECORD statement) and zero or more levels of aggregate field names.
You can assign an aggregate field to another aggregate field (record =
record) only with records having the same structure . VAX FORTRAN
supports no other operations (such as arithmetic or comparison) on
aggregate fields.
Aggregate field references can be used in unformatted 1/0 statements
(one I/ O record is written no matter how many aggregate and array name
references appear in the 1/0 list) but cannot be used in formatted and
NAMELIST I/ O statements.
Aggregate field references can be used as both dummy and actual arguments. The declaration of the dummy record in the subprogram must
match the form of the record declared in the calling program unit; that is,
each structure must have the same number and types of fields in the same
order. The ordering of map fields within a union declaration is irrelevant.

Data Types, Data Items, and Expressions

2-37

Records are passed by reference . Aggrega te field references•are treated like
normal variables. Adjustable arrays can be used in RECORD statements
that are used as dummy argumen ts.
NOTE

Because periods are used in record references to separate fields,
you should not use relational operators (.EQ., .XOR.) logical
constants (.TRUE. , .FALSE.) and logical expressions (.AND. ,
.N OT:, .OR.) as field names in structure declarations.
Examples

The following examples demonstrate record and fi eld references . Consider
the following structure declarations (described at length in Section 4.15.1).
Structure DATE:
STRUCTURE / DATE/
LOGICAL*1 DAY , MONTH
INTEGER*2 YEAR
END STRUCTURE

Structure APPOINTME N T:
STRUCTURE /APPO I NTMENT/
RECORD /DATE/
APP_DATE
STRUCTURE /TIME/ APP_TIME (2)
HOUR, MI NUTE
LOGICAL*1
END STRUCTURE
APP_MEMO (4)
CHARACTER*20
APP_FLAG
LOGICAL*1
END STRUCTURE

Consider also the followi ng RECORD statement, which creates a variable
named NEXT_APP and a 10-element array named APP_LIST. Both the
variable and each element of the array take the form of the structure
APPOINTMENT.
RECORD / APPO INTMENT/ NEXT_APP, APP_LIST (10)

Each of the following examples of record and field references are derived
from the preceding structure declarations and RECORD statement.

Aggregate Field References
•

The record NE XT_APP :
NEXT_APP

2-38

Oata Types, Oata Items, and Expressions

•

The fie ld APP_TJME(l), an array fi eld of th e record NEXT_APP :
NEXT_APP . APP_TI ME( l )

•

The field APP_DATE, a 4-byte arra y field in the record array APP_
LIST(3):
APP _LI ST(3 ) APP _DATE

Scalar Field References
•

The field APP_FLAG, a LOGICAL field of the record NEXT_ APP:
NEXT _APP .APP_ FLAG

•

The field HOUR, a LOGICAL* 1 subfield of field APP_TIME(l) of
record NEXT_APP :
NEXT_APP .APP_TIME(l ) .HOUR

•

The first character of APP_MEMO(l), a CHARACTER*20 field of the
record NEXT_APP:
NEXT_APP .APP_MEM0(1) ( 1: 1)

•

The field MONTH, a LOGICAL*l subfield of field AP P_ DATE of
record array APP_ UST(l) :
APP_LI ST( l ) APP_DATE MONTH

2.2.6

Terminology Used to Refer to Data Items
Constants, variables, arrays, array elements, scalar record fields, aggregate
fields, character substrings, and expressions can be specified in many
places in a VAX FORTRAN program. FORTRAN statements and expressions have individual restrictions governing which of these items can be
used in statements and expressions and in what form. Thus, to avoid repeatedly enumerating lists of the various items that can be specified with
the various statements and expressions, the items divide into four general
categories. The names of these categories are used throughout this manual
to identify what can be included in a particular statement or expression.
The categories are as follows:
•

Scalar Reference-resolves into a reference to a single, typed data
item (a variable, scalar record field , array element, constant, character
substring, or expression).

Data Types, Data Items, and Expressions

2-39

•

•
•

Scalar Memory Reference-resolves into a data item that can be assigned a value by means of an assignment statement. It is the same as
a scalar reference, excluding constants and expressions.
Array Name Reference-resolves into a reference to an array.
Aggregate Reference-resolves into a reference to a structured data item
(a record structure or substructure).

Scalar reference, scalar memory reference, array name reference, and
aggregate reference are used throughout this manual to indicate where
these various categories of data items can be specified.
Examples

Consider the following declarations:
INTEGER INT, INTARY (10)

STRUCTURE / STRA/
I NTEGER I NTFLD, I NTFLDARY (10)
END STRUCTURE

STRUCTURE /STRB /
CHARACTER*20 CHARFLD
INTEGER I NTFLD, I NTFLDARY (10)
STRUCTURE STRUCFLD
COMPLEX CPXFLD, CPXFLDARY (10)
END STRUCTURE
RECORD /STRA / RECFLD , RECFLDARY (10 )
END STRUCTURE

RECORD

/ STRB/

REC, RECARY (10)

Each of the following references are derived from the preceding data
declarations.

2-40

Data Types, Data Items, and Expressions

Scalar References
INT
I NTARY(l)
REC . INTFLD
REC . INTFLDARY(1)
REC . RECFLD . INTFLD
REC .STRUCFLD .CPXFLD
REC .RECFLD . INTFLDARY(1)
REC .RECFLDARY(1) . I NTFLD
REC.RECFLDARY( 1) . I NTFLDARY (1)
REC .CHARFLD
REC .CHARFLD (5 :10)
RECARY(1 ) .CHARFLD(5 : 10)
RECARY (l ) . I NTFLD
RECARY(1) . INTFLDARY( 1)
RECARY (1) . RECFLD . I NTFLD
RECARY(1) .STRUCFLD .CPXFLD
RECARY (1) . RECFLD . I NTFLDARY(l )
RECARY (1 ) . RECFLDARY (1) . I NTFLD
RECARY (1) . RECFLDARY (l) .I NTFLDARY( l)

Scalar Memory References
All references listed in the scalar reference category are also in the category
of scalar memory reference because they do not include constants and
expressions.

Array Name References
I NTARY
RECARY
REC . INTFLDARY
REC. RECFLDARY
REC . RECFLD . INTFLDARY
REC .RECFLDARY(1) . I NTFLDARY
REC .STRUCFLD .CPXFLDARY
RECARY (l) . I NTFLDARY
RECARY(1) . RECFLDARY
RECARY (1) . RECFLD. INTFLDARY
RECARY (1 ) .STRUCFLD.CPXFLDARY
RECARY( 1) . RECFLDARY (1) . I NTFLDARY

Aggregate References
REC
RECARY (l )
REC.RECFLD
REC.STRUCF LD
REC.RECFLDARY(1)
RECARY (1) . RECFLD
RECARY(1 ) .STRUCFLD
RECARY(1 ) . RECFLDARY (1)

•

Data Types, Data Items, and Expressions

2-41

2.3

Expressions
An expression is a scalar field reference, function reference, or combination
of these references plus operators. Expressions represent singular values.
Combinations represent singular values because they resolve into singular
values when computations are made on their data items, as specified by
the operators.
Expressions are classified as arithmetic, character, relational, or logical.
Arithmetic expressions produce numeric values, character expressions
produce character values, and relational and logical expressions produce
logical values.

2.3.1

Arithmetic Expressions
Arithmetic expressions express numeric computations. Arithmetic expressions are formed with arithmetic elements and arithmetic operators. The
evaluation of an arithmetic expression yields a single numeric value.
An arithmetic element can be any of the following:
•
•

Numeric scalar reference
Arithmetic expression enclosed in parentheses

•

Numeric function reference

The term num eric includes logical data, because logical data are trea ted as
integer data when used in an arithmetic context.
Arithmetic operators specify a computation to be performed using the
values of arithmetic elements. They produce a numeric value as a result.
Operators and their functions are as follows:
Operator

Function

Exponentiation

Multiplication

Division

Addition or unary plus
Subtraction or unary minus

2-42

Data Types, Data Items, and Expressions

The plus and minus operators are unary operators because they can
operate on a single operand. Used as unary operators, the plus or minus
operators precede a single operand and denote a positive or negative
value, respectively. Thus, they preserve or change the arithmetic sign of
a value. The exponentiation, multiplication, and division operators are
binary operators because they operate on a pair of operands.
Variables, array elements, and field references must have defined values
before being used in an arithmetic expression.
Valid arithmetic operations must have results that are mathematically
defined. For example, dividing by zero or raising a zero-valued base to
a zero-valued or negative-valued power is invalid. Raising a negativevalued base to a real power is also invalid.
Arithmetic expressions are evaluated in an order determined by a precedence associated with each operator:
Operator

Precedence

••

First

•and/

Second

+and -

Third

When operators with equal precedence appear, they can be evaluated in
any order as long as the order is algebraically equivalent to a left-to-right
order of evaluation. Exponentiation, however; is evaluated from right to
left. For example, A**B**C is evaluated as A••(B**C); B**C is evaluated
first, and then A is raised to the resulting power.
Normally, two operators cannot appear together. However, VAX
FORTRAN allows two consecutive operators if the second operator is
a plus or minus.
Examples
In the following example, the exponentiation operator is evaluated first
because it takes precedence over the multiplication operator:
A• • B•C is evaluated as (A** B) *C.

Ordinarily, the exponentiation operator would be evaluated first in the
next example. However, because VAX FORTRAN allows the combination
of the exponentiation and minus operators, the multiplication operator is
evaluated first. The exponentiation operator must wait until the minus

Data Types, Data Items, and Expressions

2-43

operator is evaluated. As a result, the multiplication operator is evaluated
first, since it takes precedence over the minus operator:
A** - B*C is evaluated as A** <- (B* A)).

2.3. 1.1

Using Parentheses
You can use parentheses to force a particular order of evaluation. When
part of an expression is enclosed in parentheses, that part is evaluated first
and the resulting value is used in the evaluation of the remainder of the
expression.
In the following four examples, the numbers below the operators indicate
a possible order of evaluation. Alternative evaluation orders are possible
in the first three examples because they contain operators of equal precedence that are not dictated by parentheses. In these cases, the compiler
is free to evaluate operators of equal precedence in any order-as long
as the result is the same as the result gained by the algebraic left-to-right
order of evaluation.
4 + 3 * 2 - 6 I 2 = 7

(4+3)

* 2 - 6 I 2 = 11
2

(4 + 3

((4+3)

* 2 - 6) I 2 = 2
1

* 2 - 6) I 2 = 4
2

As shown in the last two examples, expressions within parentheses
are evaluated according to the normal order of precedence, unless you
override the order by using parentheses within parentheses.
Nonessential parentheses do not affect expression evaluation, as shown in
the following example:
4 + (3 * 2) - (6/2)

2-44

Data Types, Data Items, and Expressions

However, using parentheses to specify the evaluation order is often important in high-accuracy numerical computations. In such computations,
evaluation orders that are algebraically equivalent might not be computationally equivalent when processed by a computer (because of the wa y
intermediate results are rounded off).
2.3.1.2

Data Type of an Arithmetic Expression
If every element in an arithmetic expression is of the same data type, the
value produced by the expression is also of that data type. If elements
of different data types are combined in an expression, the evaluation of
that expression and the data type of the resulting value depend on a rank
associated with each data type. The rank assigned to each data type is as
follows:
Data Type

Rank

Logical

1 (Lowest)

INTEGE R*2

INTEGER*4

REAL*4 (REAL)

REAL*8 (DOUBLE PRECISION)

REAL*l6

COMPLEX*8 (COMP LEX)

COMPLEX* 16 (DOUBLE COMPLEX)

8 (H ig hest)

The data type of the value produced by an operation on two arithmetic
elements of different data types is the data type of the highest-ranked
element in the operation. For example, the data type of the value resulting
from an operation on an integer and a real element is real. However,
an operation involving a COMPLEX*8 data type and either a REAL* 8 or
REAL* 16 da ta type produces a COMPLEX* 16 result.
The data type of an expression is the data type of the result of the last
operation in that expression and is determined according to the following
conventions:

•

Integer operations: Integer operations are performed only on integer
elements. (Logical entities used in an arithmetic context are treated

Data Types, Data Items, and Expressions

2-45

as integers .) In integer arithmetic, any fraction that can result from
division is truncated, not rounded. For example:
1/4 + 1/4 + 1/4 + 1/4

•

The value of this expression is 0, not 1.
Real operations: Real operations are performed only on real elements
or combinations of real, integer, and logical elements. Any integer
elements present are converted to the real data type by giving each a
fractional part equal to zero. The expression is then evaluated using
real arithmetic. However, in the statement Y = (I/ J) *X, an integer
division operation is performed on I and J, and a real multiplication is
performed on that result and X.
REAL*B and REAL*l 6: operations: Any element in an operation in which
there is a higher-precision element is converted to the data type of the
higher-precision element by making the existing element the most
significant portion of the higher-precision data. The least significant
portion of the binary representation is zero. The expression is then
evaluated in the higher-precision arithmetic.

Real element to higher-precision element conversions: Converting a real
element to a higher-precision element does not increase its accuracy;
for example, a REAL variable having the value 0.3333333 is converted
approximately to 0.3333333134651184DO. It is not converted to either
0.3333333000000000DO or 0.3333333333333333DO.

•

Complex operations: In operations that contain any complex elements,
integer elements are converted to the real data type, as previously
described. The obtained REAL or REAL*8 element is then designated
as the real part of a complex number and the imaginary part is
assigned a value of zero. Next, the expression is evaluated using
complex arithmetic and the resulting value is a complex data type.
Operations involving COMPLEX*8 and REAL>1c8 elements are done as
COMPLEX* 16 operations; the REAL*8 element is not rounded!.

•

Constants defined by PARAMETER statements: If a constant was assigned a value by a PARAMETER statement, it may be treated as a
lower-order type in an arithmetic expression. This treatment can occur
even if the constant was explicitly typed. For example, an INTEGER*4
constant might be treated as ar INTEGER*2 constant.

These rules also generally apply to arithmetic operations in which one
of the operands is a constant. However, if a real or complex constant is
used in a higher-precision expression, additional precision will be retained
for the constant. The effect is as if a REAL*8 or REAL* 16 representation
of the constant had been given. For example, the expression I.ODO +
0.3333333 is treated as if it were I.ODO+ 0.3333333000000000DO.
2-46

Data Types, Data Items, and Expressions

2.3.2

Character Expressions
Character expressions consist of character elements and character opera tors. The evaluation of a character expression yields a single value with a
character data type. Character expressions take the following form:
character-element [//character-element] ...

character-element
Is any one of the following entities:

•
•

Character scalar reference
Character substring

•

Character expression, optionally enclosed in parentheses

•

Character function reference

The only character operator is the concatenation operator (/ /).
The value of a character expression is a character string formed by successive left-to-right concatenations of the values of the elements of the
character expression. The length of a character expression is the sum
of the lengths of the character elements. For example, the value of the
character expression 'AB'/ j'CDE' is 'ABCDE', which has a length of five .
Parentheses do not affect the value of a character expression; for example,
the following character expressions are equivalent:
('ABC'//'DE')//'F'
'ABC'//('DE'//'F')
'ABC'//'DE'//'F'

Each of these character expressions has the value 'ABCDEF'.
If a character element in a character expression contains spaces, the spaces
are included in the value of the character expression. For example,
'ABC'/ j'D E'//'F' has a value of 'ABC DEF'.

Data Types, Data Items, and Expressions

2-4 7

2.3.3

Relational Expressions
A relational expression consists of two arithmetic expressions or two
character expressions separated by a relational operator. A relational
operator tests for a relationship between the two expressions. The value
of the relational expression is either .TRUE. or .FALSE. depending on
whether the stated relationship holds.
VAX FORTRAN supports the following relational operators:
Operator

Relationship

.LT.

Less than

.LE.

Less than or equal to

.EQ.

Equal to

.NE .

Not equal to

.GT.

Greater than

.GE .

Greater than or equal to

Both delimiting periods are required.
Complex expressions can be related only by the .EQ. and .NE. operators.
Complex entities are equal if their corresponding real and imaginary parts
are both equal.
In an arithmetic relational expression, the arithmetic expressions are
first evaluated to obtain their values. These values are then compared
to determine whether the relationship stated by the operator holds; for
example:
APPLE+PEACH .GT . PEAR+ORANGE

This expression states the relationship, "The sum of APPLE and PEACH is
greater than the sum of PEAR and ORANGE." If that relationship holds,
the value of the expression is .TRUE. If not, the value of the expression is
.FALSE.
Similarly, in a character relational expression, the character expressions
are first evaluated to obtain their values. These values are then compared
to determine whether the relationship stated by the operator holds. In
character relational expressions "less than" means "precedes in the ASCII
collating sequence," and "greater than" means "follows in the ASCII
collating sequence;" for example:
'AB'//'ZZZ' .LT.

2-48

CCCCC

Data Types, Data Items, and Expressions

This expression states that 'ABZZZ' is less than 'CCCCC'. Because that
relationship does hold, the value of the expression is .TRUE. If the
relationship stated does not hold, the value of the expression is .FALSE.
If the two character expressions in a relational expression are not the same
length, the shorter one is padded on the right with spaces until the lengths
are equal; for example:
'ABC' .EQ . 'ABC
I

LT .

The first relational expression has a value of .TRUE. even though the
lengths of the expressions are not equal, and the second has a value of
.TRUE. even though 'AB' is longer than 'C '.
All relational operators have the same precedence. However, arithmetic and character operators have a higher precedence than relational
operators.
As in any other expression, you can use parentheses to alter the order
of evaluation of the expressions in a relational expression. However,
because arithmetic and character operators are evaluated before relational
operators, you do not need to enclose the entire arithmetic or character
expression in parentheses.
A relational expression can compare two numeric expressions of different
data types. In this case, the value of the .expression with the lowerranked data type is converted to the higher-ranked data type before the
comparison is made.

2.3.4

Logical Expressions
A logical expression is a single logical element or a combination of logical
elements and logical, arithmetic, or relational operators.
Logical elements can be any one of the following:
•

Integer or logical scalar reference

•
•

Relational expression
Integer or logical expression enclosed in parentheses

•

Integer or logical function reference

Data Types, Data Items, and Expressions

2-49

VAX FORTRAN logical operators are any one of the following:
Operator

Example

Meaning

.AND.

A . AND. B

Logical conjunction: The expression is true if
both A and B are true.

.OR.

A . OR . B

Logical disjunction (inclusive OR): The
expression is true if either A or B, or both,
are true .

.NEQV .

A . NEQV . B

Logical exclusive OR: The expression is true
if A and B have different logical values; but
the expression is false if both elements have
the same logical value.

.XOR.

A . XOR . B

Same as .NEQV .

.EQV .

A . EQV . B

Logical equivalence: The expression is true
if both A and B have the same logical value,
whether true or false.

.NOT.

. NOT . A

Logical negation: The expression is true if A
is false and false if A is true.

Delimiting periods are required. Periods cannot appear consecutively
except when the second operator is .NOT. For example, the following
logical expression is valid:
A+B/(A- 1)

. AND . . NOT . D+B/(D-1)

Data Types that Result from Logical Operations
On logical elements, logical operations produce single logical values
(.TRUE. or .FALSE.) with a logical data type.
On integers, logical operations produce single values with an integer data
type; they are carried out bit-by-bit on corresponding bits of the internal
(binary) representation of the integer elements.
On a combination of integer and logical values, logical operations also
produce single values with an integer data type. The operation first
converts logical values to integers and then operates as it does with
integers.
Logical operations cannot be performed on other data types.

2-50

Data Types, Data Items, and Expressions

Evaluation of Logical Expressions

Logical expressions are evaluated according to the precedence of their
operators. Consider the following expression:
A*B+C*ABC . EQ . X*Y+DM/ZZ .AND. . NOT . K*B . GT . TT

This expression is evaluated in the following sequence:
( ( (A*B) + (C*ABC)) . EQ . ( (X *Y) + (DM/ZZ))) . AND. ( .NOT. ( (K *B) . GT. TT))

The following list identifies all the operators that can appear in a logical
expression in the order of their precedence:
Operator

Precedence

First (highest)

*, I

Second

+,-,II

Third

Relational Operators

Fourth

.NOT.

Fifth

.AND.

Sixth

.OR.

Seventh

.XOR ., .EQV ., .NEQV .

Eighth (lowest)

As with arithmetic expressions, you can alter the sequence of evaluation
by using parentheses.
When operators have equal precedence, the compiler can evaluate them
in any order-as long as the result is the same as the result gained by the
algebraic left-to-right order of evaluation (except for exponentiation, which
is associated from right to left).
You should not write logical expressions whose results might depend on
the evaluation order of subexpressions. The compiler is free to evaluate
subexpressions in any order. In the following example, either (A(I)+ 1.0) or
B(I)•2.0 could be evaluated first:
(A(I)+l.O) .GT . B(I) *2 .0

Data Types, Data Items, and Expressions

2-51

Some subexpressions may not be evaluated if the compiler can determine the result by testing other subexpressions in the logical expression.
Consider the following expression:
A .AND. (F(X,Y) .GT . 2 .0) .AND. B

If A is false, and if the compiler evaluates A first, then the compiler can
determine that the expression is false and may not call the subprogram
F(X,Y).

2-52

Data Types, Data Items, and Expressions

Chapter 3

Assignment Statements
Assignment statements define the value of a data item-a variable,
array element, record (structured v ariabl~), record element, or character
substring. The expression on the right side of the assignment statement's
equal sign is evaluated and the resulting value is assigned to the data item.
VAX FORTRAN supports five assignment statements: arithmetic, logical,
character, ;aggregate, and ASSIGN.

3. 1 Arithmetic Assignment Statement
The arithmetic assignment statement assigns the value of the expression
on the right of the equal sign to the numeric scalar memory reference on
the left of the equal sign. It takes the following form:
v

v
Is a numeric scalar memory reference.

e
Is an arithmetic expression.
The equal sign does not mean "is equal to," as in mathematics. It means
"is replaced by." For example:
COUNT = COUNT + 1

This statement means, "replace the current value of the integer variable
COUNT with the sum of that current value and the integer constant 1."

Assignment Statements 3-1

Although the symbolic name on the left of the equal sign can be undefined, values must have been previously assigned to all symbolic
references in the expression on the right of the equal sign.
The expression e must yield a value that conforms to the range requirements of v. For example, a real expression that produces a value greater
than 32767 is invalid if the entity on the left of the equal sign is an
INTEGER*2 variable. Significance may be lost if an INTEGER*4 value,
which can exactly represent values of approximately the range -2*10**9
to +2*10**9, is converted to REAL*4 (including the real part of a complex
constant), which is accurate to only about seven digits.
If v has the same data type as that of the expression on the right, the
statement assigns the value directly. If the data types are different, the
value of the expression is converted to the data type of the entity on the
left of the equal sign before it is assigned.

Examples

The following examples demonstrate valid and invalid assignment statements and explain why the invalid ones are not valid:
Valid
BETA= -1./(2 .*X)+A*A/(4. * (X*X))
PI= 3 . 14159
SUM = SUM + 1 .

NEW= RECORD 1 .FIELD1

Invalid

Explanation

3 . 14 = A - B

Entity on the left must be a numeric
scalar memory reference.

-J = I **4

Entity on the left must not be signed .

ALPHA= ((X+6)*B*B/(X-Y)

Left and right parentheses do not balance.

!COUNT= A//8(3 :7)

Expression on the right cannot have a
character data type if the entity on the
left does not.

Table 3-1 summarizes the data conversion rules for assignment statements .

3-2

Assignment Statements

Table 3-1:
Scala r
Memo r y
R e fere n ce
(V)

Conversion Rules for Assignment Statements
Ex pression (E)
Intege r or
Logical

REAL

REAL 0 8

R E AL-1 6

COM PL EX

COMPL EX 0 16

Integer
or Logica l

Assign E to V

Truncate E to
integer and
assign lo V

Truncate E to
integer and
assign to V

T runcate E w
in tege r a nd
assign to V

Truncate real part
of E to integer and
assign to V;
imaginary part of E
is not used

T ru ncate real pa rt of E
to in tege r a nd assign to
V; imagi na ry part of E
is no t used

REAL

Append frac tion
(.0) to E a nd
assign to V

Assign E to V

Assign MS• portion
of E to V; LS•
portion of Eis
rounded

Ass ign MS • po rt ion

of E to V: LS •
port ion of E is
ro u nded

Ass ign real pa rt of
E to V; imaginary
pa rt of E is not
used

Assig n MS • port ion
of the rea l pa rt of
E to V; LS • port io n
of the rea l part of
E is ro unded:
imagina ry pa rt of
E is not used

Append frac t ion
(.0) to E and

Ass ign E to MS•
portion of V; LS•

Ass ign E to V

Sa me as above

assiJ:{n to V

portion of V is 0

Ass ign real pa rt of
E to MS• of V;
LS• portion of V
is 0: imaginary part
of E is not used

Assign rea l pa rt o f
E to V; imagi na ry
pa rt of E is not used

Sa me as abo\'e

Sa me as abo" e

Assign E to MS•

Ass ign E to V

Same as above

Assign real pa rt of
E to MS• po rt ion
of V; LS • port ion
of rea l pa rt of V
is 0. Imagina ry pa rt
of E is not used

Ass ig n MS • portion
of E lo rea l part of
V; LS • po rt ion o f
E is rou nded:
imal(inary part o f
V is 0.0

Assign E to V

Assign MS • port ion
of real part of E to
real pa rt of V; LS •
port ion of rea l pa rt
of E is ro u nded .

REAL• 8

RE AL• I6

port ion of V : L S •

port ion of V is U

COMPLEX

Append frac tion
(.0) to E a nd
assign lo rea l
part of V;
imagina ry pa rt of
Vis 0.0

Assign E to rea l
part of V:
imagina ry pa rt
of Vis 0.0

Assign MS • portion
of E to rea l part of
V; LS• port ion of
E is rounded :
imal(ina ry part of
V is 0.0

Assign MS • po rtio n of

imagi na ry part of E
to imagi nary part of
V: LS • portion of
imag inary pa rt of E
is ro unded .
COMP LEX • I6

Append fraction
1.0) to E and ass ign
lo V: imagina ry

pa rt of V is 0.0

Assign E to MS •
po rt ion n f rea l

part o f V:
imag ina ry pa rt
11f V is 0.0

Ass ign E to rea l
pa rt of V:
imag inary pa rt

is 0.0

Sa me as above

Ass ign real pa rt of
E to MS • portion
of real pa rt of V:
LS • portion of
rea l pa rt is 0. Ass ign
imagina ry part of E
to MS • por t ion of
imagi na ry pa rt of V:
LS • portion of

Ass ign E to V

imag ina ry pa rt is 0.

'MS = most s ignifi ca nt (h igh o rder )
LS = least signiti ca nt (low order)

ZK-481 2-85

Assignment Statements

3-3

3.2

Logical Assignment Statement
The logical assignment statement assigns the value of the logical expression on the right of the equal sign to the logical scalar memory reference
on the left of the equal sign.
A logical assignment statement takes the following form :
v = e

v
Is a logical scalar memory reference.

e
Is a logical, integer, or arithmetic expression.
Values must have previously been assigned to all symbolic references that
appear in the expression. The expression must yield a logical value.
Examples

The following examples demonstrate valid logical assignment statements:
PAGEND = .FALSE.
PRNTOK = LINE . LE . 132 .AND . . NOT. PAGEND
ABIG = A.GT.B .AND. A.GT.C .AND . A.GT .D

3.3 Character Assignment Statement
The character assignment statement assigns the value of the character
expression on the right of the equal sign to the character scalar memory
reference on the left of the equal sign. It takes the following form:
v = e

v
Is a character scalar memory reference.

e
Is a character expression.
If the length of e is greater than the length of v, the character expression
is truncated on the right.
3-4 Assignment Statements

If the length of e is less than the length of v, the character expression is
filled on the right with spaces.

The expression e must have a character data type. You cannot assign a
numeric value to a character scalar memory reference.
By assigning a value to a character substring, you do not affect character
positions in the character scalar memory reference not included in the
substring. If a character position outside of the substring has a value
previously assigned, it remains unchanged. If the character position is
undefined, it remains undefined.
Examples

The following examples demonstrate valid and invalid character assignment statements and explain why the invalid ones are not valid. (In the
examples, all memory references have a character data type.)
Valid
FILE = 'PRDG2'
REVOL(1) = 'MAR'//'CIA'
LOCA(3 :8) = 'PLANT5'
TEXT(I,J+1)(2:N-1) =NAME/IX

Invalid

Explanation

'ABC' = CHARS

Left element must be a character variable,
array element, or substring reference.

CHARS = 25

Expression on right must have a character
data type .

STRING = 5HBEGI N

Expression on right must have a character
data type-Hollerith constants are numeric,
not character.

Assignment Statements

3-5

3.4 Aggregate Assignment Statement
The aggregate assignment statement assigns the value of each field of the
aggregate on the right of an equal sign to the corresponding field of the
aggregate on the left. Both aggregates must be declared with the same
structure.
An aggregate assignment statement takes the following form:
v = e

v
Is an aggregate reference with the same structure as the aggregate represented by e (see Section 2.2.5.1).
e
Is an aggregate reference with the same structure as the aggregate represented by v (see Section 2.2.5.1).

Example

The following example demonstrates valid aggregate assignments:
STRUCTURE /DATE/
LOGICAL*1 DAY. MONTH
I NTEGER*2 YEAR
END STRUCTURE
RECORD /DATE/ TODAY, THIS_WEEK(7)
STRUCTURE /APPOI NTMENT/
RECORD /DATE/ APP_DATE
END STRUCTURE
RECORD /APPOI NTMENT/ MEETI NG
DO I = 1,7
CALL GET _DATE (TODAY)
THIS _WEEK (I) = TODAY
THIS _WEEK (I) .DAY = TODAY . DAY + 1
END DO
MEETI NG.APP _DATE =TODAY

3-6 Assignment Statements

3.5 ASSIGN Statement
The ASSIGN statement assigns a statement label value to an integer
variable. The variable can then be used as either a transfer destination
in a subsequent assigned GO TO statement or a format specifier in a
formatted I/O statement. ASSIGN statements take the following form:
ASSIGN s TO v

s
Is the label of an executable statement or a FORMAT statement in the
same program unit as the ASSIGN statement.

v
Is an integer variable.
The ASSIGN statement assigns the statement number to the variable. It
is similar to an arithmetic assignment statement with one exception: the
variable becomes defined as a statement label reference and undefined as
an integer variable.
An ASSIGN statement must be executed before the statements in which
the assigned variable is used. Additionally, the ASSIGN statement and
the statements in which the assigned variable is used must occur in the
same program unit; for example:
ASSIGN 100 TO NUMBER

This statement associates the variable NUMBER with the statement
label 100. Once the ASSIGN statement associates a statement label to
a variable, arithmetic operations on the variable produce unpredictable
run-time behavior; for example:
NUMBER = NUMBER + 1

To return the variable to the status of an integer variable, you could use .
the following statement, which dissociates NUMBER from statement 100
and assigns it an integer value of 10:
NUMBER = 10

Once returning the variable NUMBER to its integer variable status, it can
no longer be used in an assigned GO TO statement.

Assignment Statements 3-7

Examples

The following additional examples demonstrate valid ASSIGN statements:
ASSIGN 10 TO NSTART
ASSIGN 99999 TO KSTOP
ASSIGN 250 TO ERROR

In the last example, ERROR must be previously defined as an integer
variable.

3-8 Assignment Statements

Chapter 4

Specification Statements
Specification statements are nonexecutable statements used to allocate
and initialize variables, arrays, records, and structures; and to define other
characteristics of symbolic names used in a program.
VAX FORTRAN supports the following specification statements:
•

•
•
•
•
•

BLOCK DATA-initiates a series of statements that establish common
blocks and assign initial values to entities in named common blocks
(Section 4.1).
COMMON-defines one or more contiguous areas of storage
(Section 4.2).
DATA-assigns initial values to variables, arrays, and array elements
before program execution (Section 4.3).
Data type declaration statements-explicitly define the data type of
specified symbolic names (Section 4.4).
DIMENSION-defines the number of dimensions in an array and the
number of elements in each dimension (Section 4.5).
EQUIVALENCE-associates two or more entities with the same
storage location (Section 4.6).

•

EXTERNAL-allows use of user-supplied procedures as arguments to
subprograms (Section 4.7).

•

IMPLICIT-overrides the implied data type of symbolic names
(Section 4.8).

•

INTRINSIC- allows use of FORTRAN intrinsic functions as arguments
to subprograms (Section 4.9).

•

NAMELIST-specifies lists of entities whose values may be read or
written in namelist-directed I/O statements; associates the list with
specified group-names (Section 4.10).
Specification Statements 4-1

•
•
•
•
•
•

4.1

PARAMETER-associates a symbolic name with a constant value
(Section 4.11).
PROGRAM-assigns a symbolic name to a main program unit
(Section 4.12).
RECORD-establishes a record with the structure defined by the block
of statements in a structure declaration (Section 4.13).
SAVE-retains values of local variables after a return from a subprogram (Section 4.14).
Structure declaration block-specifies the structure (form) of a record
(Section 4.15).
VOLATILE- prevents optimizations from being performed on specified variables, arrays, and common blocks (Section 4.16).

BLOCK DATA Statement
A BLOCK DATA statement initiates a series of specification statements
that establish common blocks and assign initial values to the entities in
named common blocks.
The BLOCK DATA statement takes the following form:
BLOCK DATA [narn]

nam
Is a symbolic name.

Syntax Rules and Behavior

A BLOCK DATA statement and its associated specification statements are
a special kind of program unit, called a block data subprogram . The block
data subprogram has the following syntax rules:
•

Any of the following specification statements can appear in a block
data subprogram:
COMMON
DATA
DIMENSION
EQUIVALENCE
IMPLICIT
PARAMETER
RECORD

4-2

Specification Statements

SAVE
Structure decl aration
Type declaration statements
•

A block data subprogram must not contain any executable statements.

•

As with other types of program units, the last statement in a block
data subprogram must be an END statement.

•

Within a block data subprogram, if a DATA statement initializes
any entity in a named common block, the subprogram must have a
complete set of specification statements that establishes the common
block. However, all of the the entities in the block do not have to be
assigned initial values in a DATA statement.

•

One block data subprogram can establish and define initial values for
more than one common block.

•

The name of a block data subprogram can appear in the EXTERNAL
statement of a different program unit to force the VMS Linker to
search object libraries for the BLOCK DATA program unit at link time.

Example

The following example demonstrates a valid block data subprogram:
BLOCK DATA BLKDAT
INTEGER S,X
LOGICAL T,W
DOUBLE PRECISION U
DIMENSION R(3)
COMMON /AREA1/R,S ,T,U /AREA2/W , X, Y
DATA R/1 . 0,2*2 .0/ , Tl .FALSE./ , U/0 .214537D-7/, WI .TRUE./, Y/3 .5/
END

4.2 COMMON Statement
A COMMON statement defines one or more contiguous areas, or blocks,
of storage. COMMON statements also define the order in which variables,
arrays, and records are stored in each common block.
A symbolic name identifies each block. However, you can omit a symbolic
name for one block in a program unit. The block without a name is
known as the blank common block.

Specification Statements 4- 3

The COMMON statement takes the following form:
COMMON [/[cb]/]nlist[[ , ] /[cb]/nlist] ...

cb
Is a symbolic name, called a common block name; cb can be blank. If the
first cb is blank, you can omit the first pair of slashes.

nlist
Is a list of variable names, array names, array declarators, and record
names separated by commas.
Syntax Rules and Behavior

Any common block name, blank or otherwise, can appear more than
once in one or more COMMON statements in a program unit. The list
following each successive appearance of the same common block name
is treated as a continuation of the list for the block associated with that
name.
You can use array declarators in the COMMON statement to define arrays.
A common block can have the same name as a variable, array, record,
structure, or field. However, in a program with one or more program
units, a common block cannot have the same name as a function, subroutine, or entry name in the executable program.
When common blocks from different program units have the same name,
they share the same storage area when the units are combined into an
executable program.
Entities are assigned storage in common blocks on a one-for-one basis.
Thus, the entities assigned by a COMMON statement in one program unit
should agree with the data type of entities placed in a common block by
another program unit; for example, consider a program unit containing the
following statement:
COMMON CENTS

And consider another program unit containing the following statements:
I NTEGER*2 MONEY
COMMON MONEY

When these program units are combined into an executable program,
incorrect results may occur if the 2-byte integer variable MONEY is
made to correspond to the lower-addressed two bytes of the real variable
CENTS.
4-4 Specification Statements

Example

In the following example, the COMMON statement in the main program
puts HEAT and X in the blank common block, and KILO and Q in a
named common block, BLKl.
The COMMON statement in the subroutine makes ALFA and BET share
the same storage location as HEAT and X in the blank common block.
It makes LIMA and R share the same storage location as KILO and Q in
BLKl.
Main Program

Subprogram

COMMON HEAT,X /BLK1/KILO , Q

SUBROUTINE FIGURE
COMMON /BLK1/LIMA,R I /ALFA .BET

CALL FIGURE
RETURN
END

4.3 DATA Statement
The DATA statement assigns initial values to variables and array elements
before program execution. It takes the following form:
DATA nlist/clist/[[.] nlist/clist/] ...

nlist
Is a list containing any combination of variable names, array names,
array element names, character substring names, and implied-DO lists.
Elements in the list must be separated by commas.
Subscript expressions and expressions in substring references must be
integer expressions containing integer constants and implied-DO variables.
An implied-DO list in a DATA statement takes the following form:
(dlist, i=n1 ,n2[ , n3])

Specification Statements 4-5

dlist
Is a list of one or more array element names, character substring
names, or implied-DO lists, separated by commas.
I

Is the name of an integer variable.
n1 ,n2,n3
Are integer constant expressions. The expression can contain impliedDO variables of other implied-DO lists that have this implied-DO list
within their ranges.

clist
Is a list of constants separated by commas; dist constants take one of the
following forms:
c
n

* c

c
Is a constant or the symbolic name of a constant.

n
Defines the number of times the same value is to be assigned to
successive entities in the associated nlist; n is a nonzero, unsigned
integer constant or the symbolic name of an integer constant.
Syntax Rules and Behavior

The DATA statement assigns the constant values in each dist to the
entities in the preceding nlist, from left to right, as they appear in the nlist.
The number of constants must equal the number of entities in the nlist.
When an unsubscripted array name appears in a DATA statement, values
are assigned to every element of that array in the order of subscript
progression. The associated constant list must contain enough values to
fill the array.
The following list describes the relationship between nlist items and dist
items:
•

If both the constant value in dist and the entity in nlist have numeric
data types, conversion is based on the following rules:
If necessary, the constant value is converted to the data type of
the variable being initialized.

4-6

Specification Statements

When an octal or hexadecimal constant is assigned to a variable
or array element, the number of digits that can be assigned
depends on the data type of the data item. If the constant contains
fewer digits than the capacity of the variable or array element,
the constant is extended on the left with zeros. If the constant
contains more digits than can be stored, the constant is truncated
on the left.
•

If the constant value in dist and the entity in nlist are both of character
data type, the conversion is based on the following rules:
If the constant contains fewer bytes than the length of the entity,
the rightmost character positions of the entity are initialized with
spaces.
If the constant contains more bytes than the length of the entity,
the character constant is truncated on the right.

•

If the constant value in dist is of numeric data type and the entity
in nlist is of character data type, the constant and the entity must
conform to the following restrictions:

The character entity must have a length of one character.
-

The constant must be an integer, octal, or hexadecimal constant
and must have a value in the range 0 through 255.

When the dist constant and the nlist entity conform to these restrictions, the nlist entity is initialized with the character that has the
ASCII code specified by the dist constant. (This behavior lets you
initialize a character entity to any 8-bit ASCII code.)
•

If the constant value in dist is a Hollerith or character constant and
the entity in nlist is a numeric variable or numeric array elem ent, the
number of characters that can be assigned depends on the data type
of the data item (see Table 3-1). If the Hollerith or character constant
contains fewer characters than the capacity of the variable or array
element, the constant is extended on the right with spaces. If the
constant contains more characters than can be stored, the constant is
truncated on the right.

Specification Statements 4-7

Examples

In the following example, the first DATA statement assigns zero to all 10
elements of array A and 4 asterisks followed by 2 spaces to the character
variable STARS. The second DATA statement assigns ASCII control
character codes to the character variables BELL, TAB, LF, and FF. The last
DATA statement uses an implied-DO loop to assign values to the odd
numbered elements in the array B.
I NTEGER A(10), B(10)
CHARACTER BELL, TAB, LF , FF , STARS*6
DATA A.STARS /10*0, ' ****' /
DATA BELL ,TAB,LF ,FF /7,9 , 10 , 12/
DATA (B(I), 1=1,10 ,2) /5 *1/

4.4

Data Type Declaration Statements
Type declaration statements explicitly define the data type of specified
symbolic names. There are two forms of type declaration statements:
numeric type declarations and character type declarations.
Type declaration statements can initialize data in the same wa y as the
DATA statement: by having values, bounded by slashes, listed immediately after the symbolic name of the entity.
Syntax Rules

The following rules apply to type declaration statements:

4.4.1

•

Type declaration statements must precede all executable statements.

•
•

The data type of a symbolic name can be declared only once.
Once a symbolic name has been used in a context that implicitly
assumes a data type, its assumed type cannot be changed by a type
declaration statement.

Numeric Type Declaration Statements
Numeric type declaration statements take the following form:
type :*n )v [*n] [/cli s t / ] [ , v :*n] [/clist / J) .. .

4-8

Specification Statements

type
Is any one of the following data type specifiers:

BYTE
LOGICAL
INTEGER
REAL
DOUBLE PRECISION
COMPLEX
DOUBLE COMPLEX
BYTE and LOGICAL*l are equivalent.
*n
Is an integer that specifies (in bytes) the length of v. It overrides the
length that is implied by the data type .

The value of *n must specify an acceptable length for the type of v, as
listed in Table 2.1. BYTE, DOUBLE PRECISION, and DOUBLE COMPLEX
data types have on e acceptable length; thus, for th ese data types, the *n
specifier is invalid .
If an array declarator is used, the *n specifier must be positioned immediately after the array name.

v
Is the symbolic name of a constant, variable, array, array declarator,
statement function, or function subprogram.
c/ist
Is a list of constants, as in a DATA statement. If v is the symbolic name of
a constant, the dist cannot be present. (See Section 4.3.)

Syntax Rules and Behavior

A numeric data type declaration statement can define arrays by including
array declarators in the list (see Section 2.2.3.1).
A numeric type declaration statement can assign initial values to variables
or arrays if it specifies a list of constants (the dist). The specified con stants
initialize only the variable or array that immediately precedes them. The
d ist cannot have more than one element unless it initializes an arra y.
When the d ist initializes an array, it must contain a value for every
element in the array.

Specification Statements 4-9

Examples

In the following example, the first statement declares COUNT and SUM
as integers, and MATRIX as a two-dimensional array of integers.
INTEGER COUNT, MATRIX(4,4), SUM
REAL MAN, MU
LOGICAL SWITCH

The next example shows instances where one declaration overrides
another. In the first statement, M12•4 and IVEC•4 override INTEGER•2.
In the second statement, WX3•4 and WX6•4 override REAL•8. In the third
statement, QARRAY is initialized with implicit conversion of the REAL•4
constants to a REAL•16 data type.
I NTEGER*2 I, J , K, M12*4 , Q, IVEC*4 (10)
REAL*B WX1, WXZ, WX3*4 , WX5 , WX6*4
REAL*16 PI/3 . 14159QO/, E/2 . 72QO/ , QARRAY (10)/5*0 .0 ,5*1.0/

4.4.2

Character Type Declaration Statements
Character type declaration statements take the following form:
CHARACTER[*len[,]] v[*len] [/clist / ] [.v[*len] [/clist/) ] . ..

Jen
Is an unsigned integer constant, an integer constant expression enclosed
in parentheses, or an asterisk enclosed in parentheses. The value of len
specifies the length of the character data elements.

v
Is the symbolic name of a constant, variable, array, array declarator,
statement function, or function subprogram.
clist
Is a list of constants, as in a DATA statement. (See Section 4.3.) If v is the
symbolic name of a constant, the d ist must not be present.

Syntax Rules and Behavior
If you use CHARACTER•len, len is the default length specification for
that list. If an item in that list does not have a length specification, the
item's length is len. However, if an item does have a length specification,
it overrides the default length specified in CHARACTER•len.

4-1 0

Specification Statements

When an asterisk length specification *(*) is used for a function name or
dummy argument, it assumes the length of the corresponding function
reference or actual argument (see Chapter 2). Similarly, when an asterisk
length specification is used for the symbolic name of a constant, the name
assumes the length of the actual constant it represents. For example,
STRING assumes a 9-byte length in the following statements:
CHARACTER*(*) STRI NG
PARAMETER (STRING= 'VALUE IS : ')

The length specification must range from 1 to 65535. If there is no length
specification, a length of 1 is assumed.
Character type declaration statements can define arrays if they include
array declarators (see Section 2.2.3.1) in their list. The array declarator
goes first if both an array declarator and a length are specified.
A character type declaration statement can assign initial values to variables
or arrays if it specifies a list of constants (the dist). The specified constants
initialize only the variable or array that immediately precedes them. The
dist cannot have more than one element unless it initializes an array.
When the dist initializes an array, it must contain a value for every
element in the array.
Examples

The following examples demonstrate valid and invalid character type
declaration statements:

Valid
The first example specifies an array, NAMES, with one hundred 32character elements; an array, SOCSEC, with one hundred 9-character
elements; and a variable, NAMETY, that is 10 characters long and has an
initial value of 'ABCDEFGHIJ ' .
CHARACTER*32 NAMES(100) ,SOCSEC(100) *9, NAMETY *10/ 'ABCDEFGHIJ '/

In the next example, the CHARACTER statement specifies two 8-character
variables, LAST and FIRST (the PARAMETER statement is described in
Section 4.11).
PARAMETER (LENGTH=4)
CHARACTER*(4+LENGTH) LAST , FIRST

Specification Statements

4-11

In the next example, the CHARACTER statement specifies an array,
LETTER, with twenty-six 1-character elements; and a dummy argument,
BUBBLE, that has a passed length defined by the calling program.
SUBROUTINE S1(BUBBLE)
CHARACTER LETTER(26), BUBBLE*(*)

Invalid
The following CHARACTER statement is invalid because the length
specified for BIGCHR is too large and the length specifier for QUEST is
not an integer constant expression:
CHARACTER*16 BIGCHR*(60000*2). QUEST*(5*INT(A))

4.5

DIMENSION Statement
The DIMENSION statement defines the number of dimensions in an array
and the number of elements in each dimension . It takes the following
form:
DIMENSION a(d) [ ,a(d)] .. .

a(d)

Is an array declarator. (See Section 2.2.3.1.)
Syntax Rules and Behavior

The DIMENSION statement allocates a number of storage elements to
each array named in the statement, one storage element to each array element in each dimension. The size of each storage element is determined
by the data type of the array.
The total number of storage elements assigned to an array is equal to the
number produced by multiplying together the number of elements in each
dimension in the array declarator. For example, the following statement
defines ARRAY as having 16 real elements of 4 bytes each and defines
MATRIX as having 125 integer elements of 4 bytes each:
DIMENSION ARRAY(4 ,4) , MATRIX(5 , 5,5)

Although arrays can also be declared in type declaration and COMMON
statements, array names can appear in only one array declarator in each
program unit. For further information on arrays and the storage of array
elements, see Section 2.2.3.

4-12 Specification Statements

DIMENSION has the same form and effect as the VIRTUAL statement.
(The VIRTUAL statement is described in Appendix D.)
Examples

The follo wing examples demonstrate valid DIMENSION statements:
DI MENSION BUD(12 , 24 , 10)
DIMENSION X(5,5 , 5) , Y(4,85), Z(100)
DIMENSION MARK(4 ,4 , 4 ,4)
SUBROUTINE APROC(A1,A2, N1,N2 ,N3)
DIMENSION A1( N1 :N 2) , A2(N3 :*)

4.6 EQUIVALENCE Statement
The EQUIVALENCE statement partially or totally associates two or more
entities in the same program unit with the same storage location. It takes
the following form:
EQUIVALENCE (nlist) [ , (nlist)] . . .

nlist
Is a list of variables, arrays, array elements, or character substring references, separated by commas. The list must contain at least two of these
entities.
Each expression in a subscript or a substring reference must be an integer
constant expression. Records, record fields, and dummy arguments cannot
be specified in EQUIVALENCE statements.
Syntax Rules and Behavior

The EQUIVALENCE statement causes all of the entities in one parenthesized list to be allocated storage beginning at the same storage location.
Entities having different data types can be associated because multiple
components of one data type can share storage with a single component
of a higher-ranked data type. For example, if you make an integer variable
equivalent to a complex variable, the integer variable shares storage with
the real part of the complex variable.

Specification Statements 4-13

Examples

In the first example, the EQUIVALENCE statement makes the four elements of the integer array IARR occupy the same storage as that of the
double-precision variable DYAR.
DOUBLE PRECISION DVAR
I NTEGER*2 IARR(4)
EQUIVALENCE (DVAR, IARR(1))

In the second example, the EQUIVALENCE statement makes the first
character of the character variables KEY and STAR share the same storage
location. The character variable STAR is equivalent to the substring KEY
(1:10).
CHARACTER KEY*16, STAR*10
EQUIVALENCE (KEY , STAR)

4.6. 1 Making Arrays Equivalent
When you make an element of one array equivalent to an element of
another array, the EQUIVALENCE statement also sets equivalences
between the other elements of the two arrays . Thus, if the first elements
of two equal-sized arrays are made equivalent, both arrays share the same
storage space. If the third element of a 7-element array is made equivalent
to the first element of another array, the last five elements of the first array
overlap the first five elements of the second array.
Two or more elements of the same array should not be associated with
each other in one or more EQUIVALENCE statements. For example, you
cannot use an EQUIVALENCE statement to associate the first element
of one array with the first element of another array, and then attempt to
associate the fourth element of the first array with the seventh element of
the other array.
Consider the following valid example:
DIMENSION TABLE (2 , 2), TRIPLE (2,2,2 )
EQUIVALENCE (TABLE(2,2) , TRIPLE ( l ,2 , 2) )

As a result, the entire array TABLE would share part of the storage space
allocated to TRIPLE. Table 4-1 shows how these statements align the
arrays.

4-14 Specification Statements

Table 4-1:

Equivalence of Array Storage

Array TRIPLE

Array TABLE

Array
Element

Element
Number

Array
Element

Element
Number

TRIPLE(l ,1,1)

TRIPLE(2, l , l)

TRIPLE( 1,2, l)

TRIPLE(2,2, 1)

TABLE(l ,1 )

TRIPLE(l, 1,2)

TABLE(2,1)

TRIPLE(2, l ,2)

TABLE(l ,2)

TRIPLE(l,2,2)

TABLE(2,2)

TRIPLE(2,2,2)

Each of the following statements also aligns the two arrays as shown in
Table 4-1:
EQUIVALENCE (TABLE , TRIPLE(2 ,2,1))
EQUIVALENCE (TRIPLE(1 , 1,2). TABLE(2 , 1))

Similarly, you can make arrays equivalent with nonunity lower bounds.
For example, an array defined as A(2:3,4) is a sequence of eight values. A
reference to A(2,2) refers to the third element in the sequence. To make
array A(2:3,4) share storage with array 8(2:4,4), you can use the following
statement:
EQUIVALENCE (A(3 ,4) , 8(2 ,4))

The entire array A shares part of the storage space allocated to array B.
Table 4-2 shows how these statements align the arrays.
Each of the following statements also aligns the arrays as shown in
Table 4-2:

Specification Statements

4-15

EQUIVALENCE (A, 8(4,1))
EQUIVALENCE (8(3,2), A(2,2))

Table 4-2:

Equivalence of Arrays with Nonunity Lower
Bounds

Array B

Array A

Array
Element

Element
Number

8(2,1)

8(3,1)

8(4,1)

Array
Element

Element
Number

A(2,1)

8(2,2)

A(3, 1)

8(3,2)

A(2,2)

8(4,2)

A(3,2)

8(2,3)

A(2,3)

8(3,3)

A(3,3)

8(4,3)

A(2,4)

B(2,4)

A(3,4)

8(3,4)

8(4,4)

Only in the EQUIVALENCE statement can you identify an array element
with a single subscript (the linear element number), even though the array
was defined as a multidimensional array . For example, the following
statemen ts align the two arrays as shown in Table 4-1:
DI MENSIO N TABLE (2 ,2) , TRIPLE (2,2 , 2)
EQUIVALENCE (TABLE (4) , TRIPLE (7))

4-16

Specification Statements

4.6.2

Making Substrings Equivalent
When you make one character substring equivalent to another character
substring, the EQUIVALENCE statement also sets equivalences between
the other corresponding characters in the character entities; for example:
CHARACTER NAME*16, ID*9
EQUIVALENCE (NAME(10 : 13) , ID(2 :5))

As a result of these statements, the character variables NAME and ID
share space as illustrated in Figure 4-1.
The following statement also aligns the arrays as shown in Figure 4-1:
EQUIVALENCE (NAME(9 :9), ID(1 : 1))

If the character substring references are array elements, the EQUIVALENCE
statement sets equivalences between the other corresponding characters in
the complete arrays.

Specification Statements 4-17

Figure 4-1:

Equivalence of Substrings

NAME
Character
Position
1
2
3
4
5
6

Character
Position

1
2

10
~

8
9
ZK-618-82

Character elements of arrays can overlap at any character position; for
example:
CHARACTER FIELDS(100) *4, STAR(5) *5
EQUIVALENCE (FIELDS(1)(2 :4), STAR(2)(3 :5))

As a result of these statements, the character arrays FIELDS and STAR
share storage space as shown in Figure 4-2.

4-18

Specification Statements

Figure 4-2:

Equivalence of Character Arrays
STAR
Cha ract er
Po si tion

Subscript

3
4

FIELDS

5
Subscript

Character
Position

4
6

2
3
4
7

~
100
2

3
4

ZK-619-82

Specification Statements 4-19

The EQUIVALENCE statement cannot assign the same storage location
to two or more substrings that start at different character positions in the
same character variable or character array. The EQUIVALENCE statement
also cannot assign memory locations in a way that is inconsistent with the
normal linear storage of character variables and arrays.

4.6.3

EQUIVALENCE and COMMON Interaction
A common block can extend beyond its original boundaries if variables or
arrays are associated with entities stored in the common block. However,
a common block can only extend beyond its last element; the extended
portion cannot precede the first element in the block.
Examples

The following examples demonstrate valid and invalid extensions of the
common block:

Valid
DIMENSION A (ll), B(G)
COMMON A
E Q U I l.J AL E NC E ( A ( 2 ) , B ( 1 ) )

A (I )

A( :Z)

A(: n

A(4 )

H( l )

H (:Z)

H (:l)
....n

8 (4)

H (f> )

•..._

Existing
Common

H (6 )

,,..,.,

Extended
Portion
ZK- 1944 - 84

Invalid
DIMENSION A(ll ) , B ( G)
COMMON A
EQLJil.JALENCE (A ( 2 ) , B(3 ) )

A( I )

AU l

A(:l)

A(4)

Hen

H( :n

8 (4)

H (f>)

H( !)

./~

'-..--'"'

Extended
Portion

8 (() )

Existing Common

Extended
Portion
ZK- 19 4 5 -84

The second example is invalid because the extended portion, B(l), precedes the first element of the common block A.

4-20 Specification Statements

4. 7 EXTERNAL Statement
EXTERNAL statements allow you to use the names of external procedures
as arguments to other subprograms.
The subprograms mentioned in the EXTERNAL statement cannot be
FORTRAN intrinsic functions; they can only be user-supplied functions,
subroutines, or block data subprograms. The INTRINSIC statement
discussed in Section 4.9 allows intrinsic function names to be used as
arguments.
The EXTERNAL statement takes the following form:
EXTERNAL v [ , v) .

v
Is the symbolic name of a user-supplied subprogram or the name of a
dummy argument associated with the name of a subprogram.
Syntax Rules and Behavior

The EXTERNAL statement declares each symbolic name included in it to
be the name of an external procedure, even if a name is the same as that
of an intrinsic function. For example, if SIN is specified in an EXTERNAL
statement (EXTERNAL SIN), all subsequent references to SIN are to a
user-supplied function named SIN, not to the intrinsic function of the
same name (see Section 6.3.1.2).
A name specified in an EXTERNAL statement can be used as an actual argument to a subprogram, and the subprogram can then use the
corresponding dummy argument in a function reference or a CALL
statement.
You can include the name of a block data subprogram in the EXTERNAL
statement to force the VMS Linker to search the object module libraries for
the block data subprogram. However, the name of the subprogram must
not be used in a type declaration statement.
Used as an argument, a complete function reference represents a value, not
a subprogram; for example, FUNC(B) represents a value in the following
statement:
CALL SUBR (A, FUNC(B), C)

Specification Statements

4-21

A complete function reference cannot be defined in an EXTERNAL statement because there is no data type information.
NOTE
The interpretation of the EXTERNAL statement described here
is different from that of earlier versions of FORTRAN produced
by DIGITAL. See Appendix A for the earlier interpretation.
See Section 4.9 for an example of EXTERNAL statements.

4.8 IMPLICIT Statement
The IMPLICIT statement overrides implied (default) data typing of symbolic names. (The default data type is INTEGER for symbolic names
beginning with the letters I through N, and REAL•4 for symbolic names
beginning with any other letter.)
The IMPLICIT statement takes one of the following forms:
IMPLICIT typ (a [,a] ... ) [. typ (a[. a] ... ) ] . ..
IMPLICIT NONE

typ
Is one of the data type specifiers (listed in Section 2.1).

When typ is equal to CHARACTER•len, len specifies the length for
character data type. Len is an unsigned integer constant or an integer
constant expression enclosed in parentheses; len must be in the range of 1
to 65535.

a
Is an alphabetic specification in either of the general forms: c or cl-c2,
where c is an alphabetic character. The latter form specifies a range of
letters, from cl through c2, where cl precedes c2 in alphabetical order.
Syntax Rules and Behavior

The IMPLICIT statement assigns the specified data type to all symbolic
names that have no explicit data type and begins with the specified
letter or range of letters. It has no effect on the default types of intrinsic
functions.

4-22

Specification Statements

The IMPLICIT NONE statement disables all implicit defaults. When
IMPLICIT NONE appears, all symbolic names in a program uni t must
be explicitly declared. No other IMPLICIT statements can appear in a
program unit containing an IMPLICIT NONE statement.
NOTE
By using the /WARNINGS= DECLARATIONS qualifier on the
FORTRAN command line, you will be issued warnings when
variables are used but not typed-without having to use the
IMPLICIT NONE statement, a language extension.
Examples

The following IMPLICIT statements represent the default in the absence
of any explicit data type specifications:
IMPLICIT INTEGER (I,J ,K,L,M,N)
IMPLICIT REAL (A - H, 0-Z )

As above, the following IMPLICIT statements assign the specified data
type in the absense of any explicit data type specification:
IMPLICIT DOUBLE PRECISION (D)
IMPLICIT COMPLEX (S , Y) , LOGICAL*l (L ,A-C )
IMPLICIT CHARACTER*32 (T- V)
IMPLICIT CHARACTER*2 (W)

4.9 INTRINSIC Statement
The INTRINSIC statement lets you use names of intrinsic functions as
arguments to subprograms. It takes the following form:
INTRI NSIC v[,v] .

v
Is the symbolic name of an intrinsic function .
Syntax Rules and Behavior

The INTRINSIC statement declares each symbolic name included in it
to be the name of an intrinsic procedure. This name can then be used
as an actual argument to a subprogram. The subprogram can then use
the corresponding dummy argument in a function reference or a CALL
statement.

Specification Statements 4-23

See Appendix D for the names and descriptions of the individual VAX
FORTRAN intrinsic functions. For further information on intrinsic functions, see Chapter 6.
Example

In the following example, when TRIG is called with a second argument of
SIN or COS, the function reference F(X) references the FORTRAN library
functions SIN and COS; but when TRIG is called with a second argument
of CTN, F(X) references the user function CTN.
Main Program

Subprogram

EXTERNAL CTN
INTRINSIC SIN, COS

SUBROUTINE TRIG(X,F,Y)
Y = F(X)
RETURN
END

CALL TRIG(ANGLE ,SIN,SINE)

FUNCTION CTN (X)
CTN = COS(X)/SIN(X)
RETURN
END

CALL TRIG(ANGLE , COS,COSINE)

CALL TRIG(ANGLE,CTN,COTANGENT)

4. 10 NAME LIST Statement
The NAMELIST statement defines a list of variables or array names and
associates that list of names with a unique group-name . The group-name
is used in the namelist-directed I/O statement to identify the variables or
arrays that are to be read or written.
NAMELIST statements take the following form :
NAMELIST /group - name / namelist[ [ , ] /group- name/ namelist] .

4-24 Specification Statements

group-name
Is a symbolic name .
nam elist
Is a list of variable or arra y names, separated by commas, that is to te
associated with the preceding group-name.

Syntax Rules and Behavior

The namelist associates a group of entities (variables or arrays) with a
single group-name, which is used by namelist-directed I/O statem ents
instead of an 1/0 list. The unique group-name identifies a list whose
entities can be modified or transferred .
You cannot include array elements, character substrings, records, and
record fields in a namelist, but you can use namelist-directed I/ O to
assign values to elements of arrays or substrings of character variables that
appear in namelists.
The namelist entities can have any data type and can be explicitly or
im plicitly typed.
Only the entities specified in the namelist can be read or written in
namelist-directed 1/0. It is not necessary for the inpu t records in a
namelist-directed in put statement to define every entity in the associated
name list.
The order of entities in the namelist controls the order in which the values
are written in the namelist-directed output. Input of namelist values can
be in any order.
A variable or an array name can appear in several namelists . Dummy
arguments cannot appear in a namelist.
Example

In the following example, the NAMELIST statement defines two groupnames: INPUT, with the entities NAME, GRADE, and DATE; and
OUTPUT, with the entities TOTAL and NAME.
CHARACTER*30 NAME(25 )
NAMELIST / I NPUT/ NAME. GRADE, DATE / OUTPUT/ TOTAL. NAME

Refer to Sections 7.2.1. 3 and 7.3 .1.3 for more inform ation on namelistdirected I/ 0.

Specification Statements 4-25

4.11

PARAMETER Statement
The PARAMETER statement associates a symbolic name with a constant
value. It takes the following form:
PARAMETER (p=c[,p=c] ... )

p
Is a symbolic name.

c
Is a constant, a compile-time constant expression, or the symbolic name of
a constant.

NOTE
The form and interpretation of the PARAMETER statement
described here are different from those of the PARAMETER
statement provided in earlier DIGITAL versions of FORTRAN.
However, VAX FORTRAN provides support for both the
FORTRAN-77 and the earlier form of the PARAMETER statement. See Appendix A for information on the earlier form and
interpretation.
Syntax Rules and Behavior

The data type of a symbolic name associated with a constant is determined
as follows:
•

By an explicit type declaration statement preceding the defining
PARAMETER statement

•

By the same rules for implicit declarations that determine the data
type of any other symbolic name
For example, the following PARAMETER statement is interpreted as
MU=l (MU has an integer data type by implication):
PARAMETER (MU=l.23)

If the PARAMETER statement is preceded by an appropriate type declaration or IMPLICIT statement, it could be interpreted as MU=l .23;
for example:
REAL*8 MU
PARAMETER (MU=l .23)

4-26

Specification Statements

Once a symbolic name is associated with a constant, it can appear
anywhere in a program that anv other constant can appear-except in
FORMAT statements (wh ere constants can only be used in variable for mat expressions) and as the character count for Hollerith constan ts. . For
compilation purposes, writing the name is the same as writing the value .
The following additional rules apply to symbolic names:
•
•

If the symbolic name is used as the length specifier in a CHARACTER
declaration, it must be enclosed in parentheses.
If it is used as a numeric item in a FORMAT edit description, it must
be enclosed in angle brackets.

•

The symbolic name of a constant cannot appear as part of another
constant, although it can appear as either th e real or imaginary part of
a complex constant.

•

A symbolic name can be defined only once within the same program
unit.
A symbolic name defined to be a constant can be used only within the
program unit containing the defining PARAMETER statement.

•

Compile-Time Constant Expressions

A compile-time constant expression can be a compile-time logical expression, a compile-time character expression, or a compile-time arithmetic
expression.
A compile-time logical expression is a logical expression with the following
characteristics:
•

•

Each operand is either a constant; the symbolic name of a constant;
one of th e intrinsic functions IAND, IOR, NOT, IEO.R ISH FT, LGE,
LGT, LLE, LLT with constant operands ~ or another compile-time
constant expression.
Each operand has a data type of logical or integer.

•

Each operator is a Boolean or relational operator.

A compile-time character expression is a character expression with the
following characteristics:
•

Each operand is either a constant, the symbolic name of a constant,
the intrinsic fun ction CHAR with a constant operand,, or another
compile-time constant expression.

Specification Statements 4-27

•
•

Each operand has a data type of character.
Each operator is the concatenation operator ( / / ).

A compile-time arithmetic expression is an arithmetic expression with the
following characteristics:
•

•
•

Each operand is either a constant; the symbolic name of a constant;
one of the intrinsic functions MIN, MAX, ABS, MOD, ICHAR, NINT,
DIM, DPROD, CMPLX, CONJG, IMAG with constant operands; or
another compile-time constant expression.
Each operand has a data type of integer, real, or complex.
Each operator is a plus, minus, multiplication, division, or exponentiation sign. (The exponentiation operator is evaluated at compile time
only if the exponent has an integer data type.)

Example

The following example demonstrates valid FORTRAN-77 PARAMETER
statements:
REAL*4 PI, PIOV2
REAL*8 DPI, DPIOV2
LOGICAL FLAG
CHARACTER*(*) LONGNAME
PARAMETER (PI=3 . 1415927, DPI=3 . 141592653589793238DO)
PARAMETER (PIOV2=PI/2, DPIOV2=DPI/2)
PARAMETER (FLAG= .TRUE ., LONGNAME='A STRING OF 25 CHARACTERS')

4.12 PROGRAM Statement
The PROGRAM statement associates a symbolic name with a main
program unit. It takes the following form:
PROGRAM nam

nam
Is the symbolic name of a source file.

4-28 Specification Statements

Syntax Rules and Behavior

The PROGRAM statement is optional. The default name for a main program unit is filename$MAIN , where filename is the name of your source
file . If filename is larger than 26 characters and a name is not specified
in a PROGRAM or BLOCK DATA statement, the name is truncated to 26
characters and $MAIN is appended to form the program name.
If you use the PROGRAM statement, it can be preceded only by an
OPTIONS statement . Otherwise, it must come first in the main program.

Its symbolic name cannot be the name of any entity within the main
program or the name of any subprogram or entry point in the same
executable program.

4.13 RECORD Statement
The RECORD statement creates a record having the form specified in
a previously declared structure (described in Section 4.15). The effect
of using a RECORD statement is comparable to that of an ordinary
FORTRAN type declaration, except composite or aggregate data items are
declared instead of scalar data items.
RECORD statements take the following form:
RECORD /structur e-narne/record - namelist
[,/structure-name/record-namelist]

[,/ structur e-name/record-narnelist]

structure-name
Is the name of a previously declared structure. See Section 4.15 .1 for a
description of structure declarations .

record-namelist
Is a list of one or more variable names, array names, or array declarators,
separa ted by commas. All of the records named in this list have the same
structure and are allocated separately in memory.

Specification Statements 4-29

Syntax Rules and Behavior

You can use record names in the following statements:
COMMON
DIMENSION
Record names cannot be used in DATA, EQUIVALENCE, NAMELIST, or
SAVE statements.
Records initially have undefined values unless you have defined their
values in structure declarations.
Examples

The following RECORD statement creates a pair of records (TODAY and
YESTERDAY) in separate memory locations, but with the same structure
(DATE):
REC ORD /DATE / TODAY.YESTERDAY

The following RECORD statement creates a record (CURRENT_CHECK)
and an array of records (CHECKBOOK) with the structure CHECK:
RECORD / CHECK/ CURRENT_ CHECK, CHECKBOOK (1000 )

4. 14 SAVE Statement
The SAVE statement causes the definition of data entities to be retained
after execution of a RETURN or END statement in a subprogram. It takes
the following form:
SAVE [a[ , a] . .. ]

a
Is the symbolic name of a common block (preceded and followed by a
slash), a variable, or an array.

4-30 Specification Statements

Syntax Rules and Behavior

A SAVE statement cannot include a blank common block, names of
entities in a common block, procedure names, and names of dummy
arguments.
Within a program unit, an entity listed in a SAVE statement does not
become undefined upon execution of a RETURN or END statement within
that program unit.
Even though a common block may be included in a SAVE statement,
individual entities within the common block could become undefined (or
redefined) in another program unit.
When a SAVE statement does not explicitly contain a list, it is treated as
though it contained a list of all allowable items in the program unit that
contains it.

NOTE
It is not necessary to use SAVE statements in VAX FORTRAN

programs. The definitions of data entities are retained automatically by VAX FORTRAN, making the use of SAVE
statements redundant. However, its use is required by the
ANSI FORTRAN Standard for programs that depend on such
retention for their correct operation. If you want your programs
to be transportable, you should include SAVE statements where
your programs would otherwise require them.
The omission of SAVE statements in necessary instances is not
flagged , even when you specify the /STANDARD qualifier on
the FORTRAN command line, because the compiler has no way
to determine whether such dependencies exist.

4. 15 Structure Declaration Block
A structure declaration block is a multistatement declaration that defines
the structure (or fo r111) of a record. It contains the following elements:
•

STRUCTURE statement - marks the beginning of a structure declaration and defining the name of the structure.

•

Declaration body - contains one or more field declarations whose
order determines the order of the fields within the structure.
Components of the declaration body are individually discussed in
this section.
Specification Statements 4-31

•

END STRUCTURE statement tion.

marks the end of a structure declara-

The Declaration Body

The declaration body can have any of the following components:

•

Typed data declaration statements: These are ordinary FORTRAN type
declarations, as described in Section 4.4. Fields can have any data
type and can be dimensioned in the normal way .

•

Substructure declarations: A field within a structure can be a substructure composed of atomic fields, other substructures, or both. There are
two ways to declare substructures:
By using RECORD statements that specify names of other, previously declared, structure declarations to be incorporated as
substructures; see Section 4.13.
By nesting structure declarations (having one or more levels of
them contained within a structure declaration) .

•

Union declarations: A union declaration declares that groups of fields
logically share a common location within a structure. Each group (one
or more fields) is individually declared by a map declaration within
the union declaration .
You use union declarations when you want to use the same area of
memory to alternately contain two or more groups of fields. Whenever
one of the fields declared by a union declaration is referenced in your
program, that field and any other fields in its map declaration become
defined. Then, when a field in one of the other map declarations in
the union declaration is referenced, the fields in that map declaration
become defined, superseding the fields that were previously defined.

•

PARAMETER statements: PARAMETER statements can appear in
a structure declaration block and have the same effect as if they
appeared outside the block. (See Section 4.11 for information about
PARAMETER statements.)

The names specified in these statements are not the names of variables
and the statements in a structure declaration do not create variables. The
nam es are field names, and the information provided in the statements
describes the layout, or form, of the structure. The ordering of both the
statements and the field names within the statements is important because
this ordering determines the order of the fields in records.
The following sections describe structure declarations, substructure declarations, and union declarations.
4-32

Specification Statements

4. 15. 1

Structure Declaration
Structure declarations define one or more fields within a VAX FORTRAN
record. This declaration defines the field names, types of data within
fields, and order and alignment of fields within a record.
Unlike type declaration statements, structure declarations do not create variables. Structured variables (records) are created when you use
a RECORD statement containing the name of a previously declared
structure. The RECORD statement can be considered as a kind of type
statement. The difference is that aggregate items, rather than single items,
are being defined.
A structure declaration takes the following form:
STRUCTURE [/structure-name/] [field-namelist]
field-declaration
[field-declaration]

[field-declaration]
END STRUCTURE

structure-name
Is the name used to identify a structure. A structure name is enclosed
by slashes. If the slashes are present, a name must be specified between
them.
Subsequent RECORD statements use the structure name to refer to the
structure. A structure name must be unique among structure names.
However, structures can share names with variables (scalar or array),
record fields, or common blocks. Thus, it is possible to have a variable named X, a structure named X, one or more fields named X, and a
common block named X.
Structure declarations can be nested (contain one or more other structure
declarations). A structure name is required for the structured declaration
at the outermost level of nesting, and optional for the other declarations
nested in it. However, if you wish to reference a nested structure in a
RECORD statement in your program, it must have a name.
Structure, field, and record names are all local to the defining program
unit. When records are passed as arguments, the fields must match in
type, order, and dimension.

Specification Statements

4-33

field-namelist
Is a list of fields having the structure of the associated structure declaration. A field namelist is allowed only in nested structure declarations .
Nested structure declarations are described in Section 4.15 .2.
field-declaration
Consists of any combination of the following types of declarations:

•

Substructure declaration : A field within a structure can be a substructure composed of atomic fields, other substructures, or a combination
of atomic fields and substructures. See Section 4.15.2 for a description
of substructure declarations.

•

Union declaration: A union declaration is composed of one or more
mapped field declarations. The mapped fields logically share a
common location within a structure. See Section 4.15.3 for a more
complete description of union declarations.

•

Field declaration: The syntax of a field declaration within a record
structure is identical to that of a normal FORTRAN type statement:
it includes a type (for example, INTEGER), one or more names of
variables or arrays; and optionally, one or more data initialization
values.

Syntax Rules and Behavior

The following rules and behavior apply to typed data declarations in
record structures:
•

%FILL can be specified in place of a field name to leave space in a
record for purposes such as alignment. This creates an unnamed field.
Unnamed fields cannot be initialized. For example, the following
statement is invalid and generates an error message:
INTEGER*4 %FILL /1980/

•

Initial values can be supplied in field declaration statements. These
initial values are supplied for all records that are declared using this
structure. Fields not initialized will have undefined values when
variables are declared by means of RECORD statements. Unnamed
fields cannot be initialized; they are always undefined.

•

All field names must be explicitly typed. There are no default names .
The IMPLICIT statement has no effect on statements within a structure
declaration.

•

All VAX FORTRAN data types are allowed in field declarations .

4-34 Specification Statements

•

•
•

Any required array dimensions must be specified in the field decla ration statements. DIMENSION statements cannot be used to define
field names.
Adjustable or assumed sized arrays and passed-length CHARACTER
declarations are not allowed in field declarations.
Field names within the same declaration level must be unique, but an
inner structure declaration (substructure declaration) can include field
names used in an outer structure declaration without conflict.

In a structure declaration, each field offset is the sum of the lengths of the
previous fields. The length of the structure, therefore, is the sum of the
lengths of its fields. The structure is packed; you must explicitly provide
any alignment that is needed by including, for example, unnamed fields of
the appropriate length.
Examples

In the first example, the declaration defines a structure named DATE .
This structure contains three scalar fields: DAY (LOGICAL*l), MONTH
(LOGICAL*l), and YEAR (INTEGER*2).
STRUCTURE /DATE/
LOGICAL*! DAY, MO NTH
I NTEGER*2 YEAR
END STRUCTURE

The following diagram shows the memory mapping of any record or
record array element with the structure DATE.
(byte offset)

field DAY

field MONTH

field YEAR

4
ZK - 1849 - 84

Specification Statements 4-35

In the second example, the declaration defines a structure named
APPOINTMENT. APPOINTMENT contains the structure DATE (field
APP_DATE) as a substructure. It also contains a substructure named
TIME (field APP_TIME, an array), a CHARACTER*20 array named APP_
MEMO, and a LOGICAL*l field named APP_ FLAG .
STRUCTURE /APPOI NTMENT/
RECORD /DATE/
APP _DATE
STRUCTURE /TIME/ APP _TIME (2)
LOGICAL*1
HOUR, MI NUTE
END STRUCTURE
APP_MEMD (4)
CHARACTER*20
APP_FLAG
LOGICAL *1
END STRUCTURE

The length of any instance of structure APPOINTME NT is 89 bytes.
The following diagram shows the memory mapping of any record or
record array element with the structure APPOINTMENT:

4-36 Specification Statements

(byte offset)

field DAY of f ield APP _ DATE

fi eld MONTH of field APP _ DATE

2
field YEAR of field APP _ DATE
3
4

field HOUR of field APP _ TIME(1)

field MINUTE of field APP _ TIME(1)

field HOUR of field APP_ TIME(2)

field MINUTE of field APP_ TIME(2)

field APP _ MEM0(1)

••
•

field APP _ MEM0(2)

•
•

•
field APP _ MEM0(3)

••
•
field APP_ MEM0(4 )

•
••
88

field APP _ FLAG

89
ZK - 1848 - 84

Specification Statements 4-37

4.15.2

Substructure Declarations
A field within a structure can itself be a structured item composed of other
fields, other structures, or both . You can declare a substructure in two
ways:

•

By nesting structure declarations within other structure or union
declarations (with the limitation that you cannot refer to a structure
inside itself at any level of nesting) .
One or more field names must be defined in the STRUCTURE statement for the substructure because all fields in a structure must be
named. In this case, the substructure is being used as a field within a
structure or union.
Field names within the same declaration nesting level must be unique,
but an inner structure declaration can include field names used in an
outer structure declaration without conflict.
%FILL can be specified in place of a field name to leave space in a
record for purposes such as alignment.

•

By using a RECORD statement that specifies another previously
defined record structure, thereby including it in the structure being
declared.

See the second example in the preceding section for a sample structure
declaration containing both a nested structure declaration (TIME) and an
included structure (DATE).

4.15.3

Union Declarations
A union declaration is a multistatement declaration defining a data area
that can be shared intermittently during program execution by one or
more fields or groups of fields.
A union declaration is initiated by a UNION statement and terminated by
an END UNION statement. Enclosed within these statements are two or
more map declarations, initiated and terminated by MAP and END MAP
statements. Each unique field or group of fields is defined by a separate
map declaration.

4-38 Specification Statements

A union declaration takes the following form:
UNION

map-declaration
map-declaration
[map-declaration]

[map-declaration]
END UNION

map-declaration
Takes the following form:
MAP

field-declaration
[field-declaration]

[field-declaration]
END MAP

field-declaration
Is a structure declaration or RECORD statement contained within
a union declaration, a union declaration contained within a union
declaration, or the declaration of a typed data field within a union.
See Section 4.15.1 for a more detailed description of what can be
specified in field declarations.

Syntax Rules and Behavior

As with normal FORTRAN type declarations, data can be initialized in
field declaration statements in union declarations. However, if fields
within multiple map declarations in a single union are initialized, the data
declarations are initialized in the order in which the statements appear.
As a result, only the final initialization takes effect and all of the preceding
initializations are overwritten.
The size of the shared area established for a union declaration is the size
of the largest map defined for that union. The size of a map is the sum of
the sizes of the fields declared within it.
As the variables or arrays declared in map fields in a union declaration are
assigned values during program execution, the values are established in a
record in the field shared with other map fields in the union. The fields
of only one of the map declarations are defined within a union at any
given point in the execution of a program. However, if you overlay one
Specification Statements 4-39

variable with another smaller variable, that portion of the initial variable
is retained that is not overlaid . Depending on the application, the retained
portion of an overlaid variable may or ma y not contain meaningful data
and can be utilized at a later poin t in the program.
Manipulating data using union declarations is similar to what happens
using EQUIVALENCE statements. The difference is tha t data entities specified within EQUIVALENCE statements are concurrently associated with a
common storage location and the data residing there; union declarations
enable you to use one discrete storage location to alternately contain a
variety of fields (arrays or variables).
With union declarations, only one map declaration within a union decla ration can be associated at any point in time with the storage location that
they share. Whenever a field within another map declaration in the same
union declaration is referenced in your program, the fields in the prior
map declaration become undefined and are succeeded by the fields in the
map declaration containing the newly referenced field .
Example

In the following example, the structure WORDS_LONG is defined. This
structure contains a union declaration defining two map fiel ds. Th e first
map field consists of three INTEGER• 2 variables (WORD_O, WORD_l ,
and WORD_2), and the second, an INTEGER•4 variable, LO NG:
STRUCTURE / WORDS _LO NG/
UNIO N
MAP
I NTEGER*2
END MAP
MAP
I NTEGER*4
END MAP
END UNIO N
END STRUCTURE

WORD _O, WORD_l, WORD_2
LO NG

The length of any record with th e structure WORDS_ LONG is six bytes.
The following diagram shows the memory mapping of any record with
the structure WORDS_LONG:

4-40

Specification Statements

t !

;;I'"

Field WORO _ O

I
! 7,

Field WORD_ 1

'-.

¥
Field LONG

/'--

{byte offs et)

j
!

Field WOR0 _ 2

..,,

Unused Space
ZK 1846 84

4.16 VOLATILE Statement
The VOLATILE statement specifies that a value is entirely unpredictable,
based on information local to the current program unit. It prevents
specified variables, arrays, and common blocks from being optimized
during compilation.
VOLATILE takes the following form:
VO LATILE nlist

nlist
Is a list of one or more variable names, named common blocks (preceded
and followed by a slash), or array names, separated by commas.
If array names or common block names are used, the entire array or
common block becomes volatile, as the following example demonstrates.

Example

In the following statements, the named common block, BLKl, and the
variables D and E are volatile. In addition, variables Pl and P4 become
volatile because the direct equivalence (in the case of Pl) and the indirect equivalence (in the case of P4) causes them to assume the volatile
attribute.

Specification Statements 4-41

PROGRAM TEST
LOGICAL *1 I PI(4)
I NTEGER*4 A, B, C, D,E, ILOOK
I NTEGER*4 P1,P2 ,P3 , P4
COMMON /BLK 1/ A,B , C
VOLATILE / BLK 1/,D ,E
EQUI VALENCE(ILOOK,I PI )
EQU I VALENCE (A,P 1)
EQUI VALENCE (P 1 ,P4)

See the VAX FORTRAN User Manual for information about the optimiza tions performed by the VAX FORTRAN compiler and the circumstances in
w hich you should use the VOLATILE declaration.

4-42

Specification Statements

Chapter 5

Control Statements
Statements normally execute in the order in which they are written.
However, you can alter the normal order of execution by transferring
control to another section of a program unit or a subprogram. Transfer of
control can be conditional or unconditional: Conditional transfer occurs
only when specified conditions are met at a certain point in a program
unit. Unconditional transfer occurs each time a certain point is reached in
a program unit.
FORTRAN control statements transfer control to a point within the same
program unit or to another program unit. These statements govern
iterative processing, suspension of program execution, and program
termination.
VAX FORTRAN supports the following control statements:
•

CALL-invokes a subroutine subprogram (Section 5.1).

•

CONTINUE-transfers control to the next executable statement
(Section 5.2).

•

DO and DO WHILE-execute a block of statements repetitively
(Section 5.3).

•
•

END DO- terminates DO and DO WHILE loops (Section 5.4).
END-marks the end of a program unit (Section 5.5).

•
•

GO TO-transfers control within a program unit (Section 5.6).
IF-conditionally transfers control or executes a statement or block of
statements (Section 5.7).

•

PAUSE-temporarily suspends program execution (Section 5.8).

Control Statements

5-1

•

RETURN-returns control from a subprogram to the calling program
unit (Section 5.9).
STOP-terminates program execution (Section 5.10).

•

5. 1 CALL Statement
The CALL statement executes a subroutine subprogram or other external
procedure. It can specify an argument list for the subroutine. The CALL
statement takes the following form:
CALL sub [ ([a] [ . [a]] . .. ) ]

sub
Is the name of a subroutine subprogram or other external procedure,
or a dummy argument associated with a subroutine subprogram or other
external procedure. See Chapter 6 for details on the definition and use of
subroutines.

a
Is an actual argument. (Section 6.1 describes actual arguments.)
Syntax Rules and Behavior
If you specify an argument list, the CALL statement associates the values
in the list with the dummy arguments in the subroutine. It then transfers
control to the first executable statement following the SUBROUTINE or
ENTRY statement referenced by the CALL statement.

The arguments in the CALL statement must agree in number, order,
and data type with the dummy arguments in the subroutine. They can
be variables, arrays, array elements. records, record elements, record
arrays, record array elements, substring references, constants, expressions,
Hollerith constants, alternate return specifiers, or subprogram names. An
unsubscripted array name or record array name in the argument list refers
to the entire array.

5-2 Control Statements

Examples

The following examples demonstrate valid CALL statements. The last
CALL statement uses statement label identifiers in its argument list. The
asterisks indicate that •10 and •20 are statement label identifiers. Label
identifiers that are prefixed by asterisks or ampersands ( & ) are called
alternate return specifiers (see Section 6.1.1.5).
CALL CURVE(BASE,3.1 4159+X ,Y,LI MIT , R(LT+2 ) )
CALL PNTOUT(A, N, 'ABCD')
CALL EXIT
RECORD /GETJP I/ GETJPIARG

CALL SYS$GETJPI (, , ,GETJPIARG , , , )
CALL MULT(A , B, *10 , *20 , C)

5.2 CONTINUE Statement
The CONTINUE statement transfers control to the next executable statement. It primarily functions as the terminal statement of a labeled DO
loop when the loop would otherwise end improperly with either a GO
TO, arithmetic IF, or other prohibited control statement.
CONTINUE takes the following form:
CONTI NUE

5.3 DO Statements
DO statements can be either one of two types:
•

Indexed (DO)

•

Pretested and indefinite (DO WHILE)

Control Statements

5-3

5.3.1

Indexed DO Statement
The indexed DO statement controls iterative processing (the statements in
its range are repeatedly executed a specified number of times). It takes the
following form:
DO [s[.JJ v=e1,e2[.e3]

s
Is the label of an executable statement. The executable statement must
physically follow the DO statement in the same program unit. The label
is optional in VAX FORTRAN .

v
Is a variable with an integer or real data type.
e1 ,e2,e3
Are arithmetic expressions.
Syntax Rules and Behavior

The variable v is the control variable; el, e2, and e3 are the initial, terminal, and increment parameters, respectively. If you omit the increment
parameter, a default increment value of 1 is used.
The optional label that appears in the DO statement identifies the terminal
statement of the DO loop. If no label appears in the DO statement, the
DO loop must be terminated by the END DO statement, as discussed in
Section 5 .4.
The terminal statement must not be one of the following statements:
•
•
•

Unconditional or assigned GO TO
Arithmetic IF
Any block IF

•
•

END
RETURN

•

The range of the DO statement includes all the statements that follow the
DO statement, up to and including the terminal statement or END DO .

5-4 Control Statements

The DO statement first evaluates the expressions el , e2, and e3 to
determine values for the initial, terminal, and increment para meters,
respectively. The increment parameter (e3) cannot be zero .
The value of the initial parameter is assigned to the control variable. If
the data type of the initial, terminal, and increment parameters are not the
same as the data type of the control variable, they are converted before
they are used.
The number of executions of the DO range, or iteration count, is given by
the arithmetic expression [(e2 - el+ e3)/e3].
The notation [e] represents the largest integer whose
magnitude does not exceed the magnitude of e and whose
sign is the same as the sign of e.
If the iteration count is zero or negative, the body of the loop is not
executed.
If the /NOF77 qualifier is specified on the FORTRAN command and th e
iteration count is zero or negative, the body of the loop executes once.

5.3. 1. 1

DO Iteration Control
After each iteration of the DO range, the following steps execute:
1.

The value of the increment parameter (e3) is algebraically added to
the control variable.

2.
3.

The iteration count is decremented.
The iteration count is evaluated and action taken as follows:
•

If the iteration count is greater than zero, control transfers to
the first executable statement after the DO statement for another
iteration of the range.

•

If the iteration count is zero, execution of the DO statement
terminates. The final value of the control variable is the value
determined by step 1.

If the control variable has a real data type, the number of iterations of the
DO range might not be what you expect because of rounding errors.

You can also terminate execution of a DO statement by using a statement
within the range that transfers control outside the loop. The control
variable of the DO statement remains defined with its current value.

Control Statements

5-5

When execution of a DO loop terminates and other DO loops share its
terminal statement, control transfers to the next outermost DO loop in the
DO nesting structure (see Section 5.3.1.2). If no other DO loop shares the
terminal statement or if the DO statement is outermost, control transfers
to the first executable statement after the terminal statement.
You cannot alter the value of the control variable within the range of the
DO statement. However, you can use the control variable for reference as
a variable within the range.
You can modify the initial, terminal, and increment parameters within the
loop without affecting the iteration count.
The range of a DO statement can contain other DO statements, as long
as these nested DO loops meet certain requirements. Section 5.3.1.2
describes these requirements.
You can transfer control out of a DO loop, but not into a loop from
elsewhere in the program. Exceptions to this rule are described in
Sections 5.3.1.3 and 5.3.1.4.
Examples

The following examples demonstrate valid and invalid DO iteration
control:

Valid
The first statement specifies 25 iterations: K=49 during the final iteration,
K=51 after the loop.
DO 100 K=1 ,50 , 2

The next statement specifies 27 iterations: J=-2 during the final iteration,
J=-4 after the loop.
DO 350 J=50 , -2 , -2

The next statement specifies 5 iterations: IVAR=S during the final iteration,
IVAR=6 after the loop.
DO 25 IVAR=1 . 5

The next statement specifies 9 iterations: NUMBER=37 during the final
iteration, NUMBER=41 after the loop. The terminating statement of the
DO loop must be END DO .
DO NUMBER=5 ,40 ,4

5-6

Control Statements

Invalid
The last statement shows how a common typing error can cause errors
with DO loops-a decimal point is typed in place of a comma. In effect,
this statement assigns 2.10 to the real variable D040M.
DD 40 M=2 .10

5.3.1.2

Nested DO Loops

A DO loop can contain one or more complete DO loops. The range of an
inner nested DO loop must lie completely within the range of the next
outer loop. Nested loops can share a labeled terminal statement but not
an END DO statement,
Table 5-1 illustrates correctly and incorrectly nested DO loops.
Table 5-1:

Nested DO Loops

Correctly Nested
DO Loops

Incorrectly Nested
DO loops

DO 45 K=1, 10

D015K=1,10

DO 35 L=2 , 50 , 2

DO 25 L=1 , 20

CONTINUE

DO 45 M=l,20

CONTINUE

DD 30 M=l,15

CONTINUE

Control Statements 5-7

Table 5-1 (Cont.):

Nested DO Loops

Correctly Nested
DO Loops

Incorrectly Nested
DO loops

DO 10 !=1 , 20

DO 10 I=1,5

DO J=1 , 5

DO J=1 , 10

DO K= 1 , 10

END DO

CONTINUE

END DO

5.3.1.3

CONTINUE

Control Transfers in DO Loops

In a nested DO loop, you can transfer control from an inner loop to an
outer loop. However, a transfer into a loop from outside that loop is not
permitted.
If two or more nested DO loops share the same terminal statement, you
can transfer control to that statement only from within the range of the
innermost loop. Any other transfer to that statement constitutes a transfer
from an outer loop to an inner loop because the shared statement is part
of the range of the innermost loop.

5-8

Control Statements

5. 3. 1.4

Extended Range

A DO loop has an extended range if it con tains a control statement
that transfers control out of the loop and if, after execution of one or
more statements, another control statement retu rns control back into the
loop. Thus, the range of the loop is extended to incl ude all executable
statem ents between the destination statement of the first transfer and the
statement that returns control to the loop.
The foll owing rules apply when using a DO loop extended range:
•

A transfer in to the range of a DO statement is permitted onl y if the
transfer is made from the extended range of tha t DO statemen t.

•

The extended range of a DO statement must not ch ange the control
variable of the DO statement.

Figure 5-1 illustrates valid and invalid extended range control transfers.

5.3.2

DO WHILE Statement
The DO WHILE statement is similar to the DO statement. However,
whereas the DO statement executes uncondi tionall y for a fixed number of
iterations, the DO WHILE statement executes conditionall y for as long as
a logical expression contained in it continues to be true . The DO WHILE
statement takes the following form :
DO [ s [ ,]] WH I LE (e)

Is the label of an executable statement that must physically follow in the
same program unit.
e
Is a logical expression .

Control Statements

5-9

Figure 5-1:

Control Transfers and Extended Range

Valid
Control Transfers

Invalid
Control Transfers

DO 35 K=1, 10

GO TO 20

DO 15 L=2,20

DO 50 K=1, 10

GO TO 20

DO 35 L=2,20

CONTINUE

A= B + C

D = E/F

DO 35 M=1, 15

CONTINUE
GO TO 40

GO TO 50
DO
Loop

A= B + C

DO 45 M=1,15

30
35

CONTINUE

D = E/F

CONTINUE

GO TO 30

CONTINUE

Extended
Range

GO TO 30
ZK -4761 ·85

5-10

Control Statements

Synt ax Rules and Behavior

The DO WHILE statement tests the logical expression at the beginning
of each execution of the loop, including the first. If the value of the
expression is true, the statements in the body of the loop are executed.
If the expression is fal se, control transfers to the statement following the
loop.
If no label appears in a DO WHILE statement, the DO WH ILE loop must
be terminated with an END DO statement (see Section 5.4) .

You can transfer control out of a DO WHILE loop but not into a loop from
elsewhere in the program.
Example

The following example demonstrates a valid DO WHILE statement:
CHARACTER*132 LI NE
I = 1

LINE(132 :) = ' x'
DO WHI LE (LINE (I : I)

. EQ. I I)

I = I + 1

END DO

5.4

END DO Statement
The END DO statement terminates the range of the DO and DO WHILE
statements. END DO is a mandatory terminator of DO blocks if the DO
or DO WHILE statement defining the blocks does not contain a terminalstatement label. If they do contain a terminal-statement label, END DO is
optional and can be used as a labeled terminal statem ent.
END DO takes the following form :
END DO

Control Statements 5-11

Examples

The following examples demonstrate mandatory and optional EN D DO
statements:
Optional

Mandatory

DO WHILE (I .GT . J)

DO 10 WH I LE (I . GT . J)

ARRAY (I , J)
I = I - 1

ARRAY (I , J ) = 1. 0
I = I - 1

1.0

END DO

5.5

END DO

END Statement
The END statement marks the end of a program unit and must be the last
source line of every program unit. It takes the following form:
END

In a main program, if control reaches the END statement, program execution terminates. In a subprogram, a RETURN statement is implicitly
executed.
If an initial line contains only an END in the statement field, it is treated
as an END statement even if it is followed by continuation lines.

5.6

GO TO Statements
GO TO statements transfer control within a program unit. Depending on
the value of an expression, control transfers to the same statement every
time GO TO executes or to one of a set of statements.
VAX FORTRAN supports three different kinds of GO TO statements:

5-12

•

Unconditional

•

Computed

•

Assigned

Control Statements

5.6.1

Unconditional GO TO Statement
The unconditional GO TO statement transfers control to the same statement every time it executes. It takes the following form:
GO TO s

s
Is the label of an executable statement that is in the same program unit as
the GO TO statement.
The unconditional GO TO statement transfers control to the statement
identified by the specified label. The label must identify an executable
statement that is in the same program unit as the GO TO statement.
Examples

The following examples demonstrate unconditional GO TO statements:
GO TO 7734
GO TO 99999

5.6.2

Computed GO TO Statement
The computed GO TO statement transfers control to a statement based
on the value of an expression within the statement. It takes the following
form:
GO TO (slist) [ , ] e

slist
Is a list of one or more labels of executable statements separated by
commas. The list of labels is called the transfer list.

e
Is an arithmetic expression in the range 1 to n (where n is the number of
statement labels in the transfer list).

Control Statements 5-1 J

Syntax Rules and Behavior

The computed GO TO statement evaluates the expression e and, if necessary, converts the resulting value to integer data type . Control is
transferred to the statement label in position e in the transfer list. For
example, if the list contains (30,20,30,40) and the value of e is 2, control is
transferred to statement 20.
If the value of e is less than 1 or greater than the number of labels in the
transfer list, control is transferred to the first executable statement after the
computed GO TO statement.
Examples

The following examples demonstrate valid computed GO TO statements:
GO TO (12 , 24 ,36) , INDEX
GO TO (320,330,340,350,360). SITU(J,K)

5.6.3

Assigned GO TO Statement
The assigned GO TO statement transfers control to a statement label that
is represented by a variable. An ASSIGN statement must establish the
relationship between the variable and a specific statement label. Thus,
the transfer destination can be changed, depending on the most recently
executed ASSIGN statement.
Assigned GO TO statements take the following form:
GO TO v[[,] (slist)]

v
Is an integer variable.

slist
Is a list of one or more labels of executable statements separated by
commas; slist does not affect statement execution and can be omitted .

5-14 Control Statements

Syntax Rules and Behavior
The assigned GO TO statement transfers control to the statement whose
label was most recently assigned to the variable v. The variable v must be
of integer data type and must have a statement label value assigned to it
by an ASSIGN statement (not an arithmetic assignment statement) before
the GO TO statement is executed.
Both the assigned GO TO statement and its associated ASSIGN statements
must exist in the same program unit. Statements that receive control must
also be in the same program unit and must be executable.
Examples
The first example is equivalent to GD TD 200:
ASSIGN 200 TD IGO
GO TD IGO

The second example is equivalent to GD TD 450:
ASSIGN 450 TD !BEG
GO TD !BEG, (300,450,1000,25)

5.7 IF Statements
IF statements conditionally transfer control or execute a statement or block
of statements. They can be any one of three kinds:
•

Arithmetic

•
•

Logical
Block (IF THEN, ELSE IF THEN, ELSE, END IF)

For each kind, the decision to transfer control or to execute the statement
or block of statements is based on the evaluation of an expression within
the IF statement.

Control Statements

5-15

5.7.1

Arithmetic IF Statement
The arithmetic IF statement conditionally transfers control to one of three
statements, based on the current value of an arithmetic expression. It
takes the following form:
IF (e) s1.s2 , s3

e
Is an arithmetic expression.

s1,s2,s3
Are labels of executable statements in the same program unit.
Syntax Rules and Behavior
All three labels (sl,s2,s3) are required, but they do not need to refer to
three different statements.
The arithmetic IF statement first evaluates the expression e. It then
transfers control to one of the three statement labels in the transfer list, as
follows:
If the value of e is:

Control passes to:

Less than 0

Label sl

Equal to 0

Label s2

Greater than 0

Label s3

Examples
The first example transfers control to statement 50 if the real variable
THETA is less than or equal to the real variable CHI. Control passes to
statement 100 only if THETA is greater than CHI.
IF (THETA-CHI) 50,50,100

The second example transfers control to statement 40 if the value of the
integer variable NUMBER is even. It transfers control to statement 20 if
the value is odd.
IF (NUMBER/2*2-NUMBER) 20,40,20

5-16

Control Statements

5. 7.2 Logical IF Statement
The logical IF statement conditionally executes a single FORTRAN statement based on the current value of a logical expression within the logical
IF statement. It takes the following form:
IF (e) st

e
Is a logical expression.

st
Is any complete, executable FORTRAN statement-except any of the block
IF statements, DO, END DO, or another logical IF statement.
The logical IF statement first evaluates the logical expression e and then
acts as follows:
•

If e is true, st executes.

•

If e is false, control transfers to the next executable statement after the
logical IF; st does not execute.

Examples

The following examples demonstrate valid logical IF statements:
IF (J .GT .4 .OR . J . LT . 1) GO TO 250
IF (REF(J,K) .NE . HOLD) REF(J,K)

= REF(J ,K) * (-1 . 500)

IF (ENDRUN) CALL EXIT

5. 7.3 Block IF Statements
Block IF statements conditionally execute blocks (groups) of statements.
They can be any one of the following:
•
•
•

IF THEN
ELSE IF THEN
ELSE

•

END IF

Control Statements

5-17

In block IF constructs, these statements take the following form:
IF (e) THEN
block

ELSE IF (el) THEN
block

ELSE
block

END IF

e
Is a logical expression.
block
Is a sequence of zero or more complete FORTRAN statements. This
sequence is called a statement block.

Syntax Rules and Behavior

Each statement in a block IF construct, except the END IF statement, has
an associated statement block. The statement block consists of all the
statements following the block IF statement up to, but not including, the
next block IF statement in the block IF construct. The statement block is
conditionally executed based on the values of the logical expressions in
the preceding block IF statements.
The functions of individual statements in a block IF construct are as
follows:
•

IF THEN-begins a block IF construct. The block following it is executed if the value of the logical expression in the IF THEN statement
is true.
NOTE
No additional statement can be placed after the IF THEN
statement in a block IF construct. For example, the following statement is invalid in the block IF construct:
IF (e) THEN I = J

This statement is translated as the logical IF statement
IF (e) THENI = J.

5-18

Control Statements

•

ELSE IF THEN-is an optional statement that specifies a statement
block to be executed if no preceding statement block in the block IF
construct has been executed, and if the value of the logical expression
in the ELSE IF THEN statement is true. A block IF construct can
contain any number of ELSE IF THEN statements.
ELSE-specifies a statement block to be executed if no preceding
statement block in the block IF construct has been executed. The ELSE
statement is optional. However, if the ELSE statement is present, the
ELSE statement block must be immediately followed by the END IF
statement.
END IF-terminates the block IF construct.

After the last statement in a statement block is executed, control passes
to the next executable statement following the END IF statement.
Consequently, no more than one statement block in a block IF construct is
executed each time the IF THEN statement is executed.
ELSE IF THEN and ELSE statements can have statement labels, but
the labels cannot be referenced. The END IF statement can have a
statement label to which control can be transferred, but only from within
the immediately preceding block.
Figure 5-2 shows the flow of control for four examples of block IF constructs.

Control Statements 5-19

Figure 5-2:

Examples of Block IF Constructs

Construct

Flow of Control

IF (e) THEN
block
END IF
Execute
block

False

IF (e) THEN
block1
ELSE
block2
END IF

IF (e 1) THEN
block 1
ELSE IF (e2) THE N
block2
END IF

Execute

block 1

block 2

Execute

block 1

block2

I F (e 1 I THE N
block 1
ELSE IF ie2) THEN
bloc k 2
ELSE IF (e3) THE N

False

block3

ELSE

Execute

E xecu te

Execute

block4
END IF

block 1

block2

block 3

block 4

ZK-617 -82

5-20 Control Statements

5. 7 .3.1

Statement Blocks

A statement block can contain any executable FORTRAN statement except
an END statement. You can transfer control out of a statement block, but
you must not transfer control into a block. Thus, you must not transfer
control from one statement block to another.
DO loops cannot partially overlap statement blocks. The DO statement
and its terminal statement must appear together in a statement block.
5.7.3.2

Block IF Examples

The following examples illustrate four variations of block IF constructs:
Variation 1: The simplest block IF construct consists of the IF THEN
and END IF statements. This construct conditionally executes one statement block, which consists of all the statements between the IF THEN and
the END IF statements.
Form

Example

IF (e) THEN

IF (ABS(ADJU) .GE. 1. 0E-6) THEN

block

TOTERR = TOTERR + ABS(ADJU)
QUEST = ADJU/FNDVAL

END IF

The IF THEN statement first evaluates the logical expression e. If the
value of e is true, the statement block is executed. If the value of e is
false, control transfers to the next executable statement after the END IF
statement, and the block is not executed.
Variation 2: The second variation contains a block IF construct with an
ELSE IF THEN statement. Blockl consists of all the statements between
the IF THEN and the ELSE IF THEN statements; block2 consists of all the

Control Statements 5-21

statements between the ELSE IF THEN and the END IF statements.
Form

Example

IF (el) THEN

IF (A .GT . B) THEN

blockl

D= B

F = A- B

ELSE IF (e2) THEN

ELSE IF (A .GT . B/2 . ) THEN
D = B/2.

block2

F = A - B/2 .

END IF

If A is greater than B, blockl is executed. If A is not greater than B but
A is greater than B/2, block2 is executed. If A is not greater than B
and A is not greater than B/2, neither blockl nor block2 is executed;
control transfers directly to the next executable statement after the END IF
statement.
Variation 3: The third variation contains a block IF construct with an
ELSE statement. Blockl consists of all the statements between the IF
THEN and ELSE statements; block2 consists of all the statements between
the ELSE and the END IF statements.

If the value of the character variable NAME is less than 'N', blockl is
executed. If the value of NAME is greater than or equal to 'N', block2 is
executed.
Form

Example

IF (e) THEN

IF (NAME

. LT . IN I) THEN

IFRONT = IFRONT + 1

blockl

FRLET(IFRONT) = NAME(1:2)

ELSE
block2

END IF

ELSE
IBACK = IBACK + 1
END IF

Variation 4: The fourth variation contains a block IF construct with
several ELSE IF THEN statements and an ELSE statement.

5-22

Control Statements

There are four statement blocks in this example. Each consists of all the
statements between the block IF statements that follow:
Block

Delimiting Block IF Statements

blockl

IF THEN and first ELSE IF THEN

block2

First ELSE IF THEN and second ELSE IF THEN

block3

Second ELSE IF THEN and ELSE

block4

ELSE and END IF

If A is greater than B, blockl is executed. If A is not greater than B but
is greater than C, block2 is executed. If A is not greater than B or C but
is greater than Z, block3 is executed. If A is not greater than B, C, or Z,
block4 is executed.
Form

Example

IF (el) THEN

IF (A .GT . B) THEN

blockl

D = B

F = A- B
ELSE IF (e2) THEN

ELSE IF (A .GT . C) THEN
D= C

block2

F = A- C
ELSE IF (e3) THEN

ELSE IF (A .GT . Z) THEN

block3

D = Z

F = A - Z

ELSE
block4

ELSE
D = 0.0
F =A

END IF

5. 7 .3.3

END IF

Nested Block IF Constructs

You can include a block IF construct in the statement block of another
block IF construct-but the nested block IF construct must be completely
contained within a statement block. It cannot overlap statement blocks.

Control Statements

5-23

The following example contains a nested block IF construct:
Form

Example

IF (el) THEN

IF (A . LT . 100) THEN
I NRAN = I NRAN + 1
IF (ABS(A-AVG) . LE . 5 . ) THEN

IF (e2) THEN

block 1

INAVG = I NAVG + 1

block la

ELSE

block lb

OUTAVG = OUTAVG + 1
END IF

END IF

ELSE

block 2

{

END IF

ELSE
OUTRAN = OUTRAN + 1
END IF

If A is less than 100, the code immediately after the IF is executed. This
code contains a nested block IF construct. If the absolute value of A minus
AVG is less than or equal to 5, blockla is executed. If the absolute value
of A minus AVG is greater than 5, blocklb is executed.
If A is greater than or equal to 100, block2 is executed, and the nested IF
construct (blockl) is not executed.

5.8

PAUSE Statement
The PAUSE statement displays a message on the terminal and temporarily
suspends program execution in order to permit you to take some action . It
takes the following form :
PAUSE [disp]

disp
Is a character constant or a string of decimal numbers (one to five digits).

5-24

Control Statements

Syntax Rules and Behavior

The disp argument is optional.
The effect of a PAUSE statement depends on how your program is being
executed. If your program is running as a batch job or detached process,
the contents of disp are written to the system output file, but the program
is not suspended.
If the program is running in interactive mode, the contents of disp are
displayed at your terminal, followed by the prompt sequence, indicating
that the program is suspended and that you should enter a command. For
example, if the following statement is executed in interactive mode:
PAUSE 'ERRONEOUS RESULT DETECTED'

You will see the following display at the terminal:
ERRONEOUS RESULT DETECTED
$

If you do not specify a value for disp, the following message is displayed
by the system:
FORTRAN PAUSE

You can respond by typing one of the following DCL commands:

5.9

•

CONTINUE-resume execution at the next executable statement.

•

EXIT-terminate execution.

•

DEBUG-resume execution under control of the VMS Debugger.

RETURN Statement
The RETURN statement transfers control from a subprogram to the
program that called the subprogram. You can use RETURN only in a
subprogram unit.
The RETURN statement takes the following form:
RETURN [i]
I

Is an optional integer constant or expression (such as 2 or I+J) that is
converted to an integer value if necessary .

Control Statements

5-25

Syntax Rules and Behavior

The optional argument, i, indicates an alternate return from the subprogram. It can be specified only in subroutine subprograms, not in function
subprograms. The value of i specifies that the ith alternate return in the
actual argument list is to be taken (see the second example that follows in
this section).
When a RETURN statement is executed in a function subprogram, control
is returned to the calling program at the statement that contains the
function reference (see Chapter 6). When a RETURN statement is executed
in a subroutine, control is returned either to the first executable statement
following the CALL statement that initiated the subroutine, or to the
statement label that was specified as the ith alternate return in the CALL
argument list.
Examples

In the first example, control is returned to the calling program at the first
executable statement following the CALL CONVRT statement.
SUBROUTINE CONVRT( N,ALPH ,DATA,PRNT,K)
INTEGER ALPH( *) , DATA(*) , PRNT( *)
IF (N .GE . 10) THEN
DATA(K+2) = N- (N/10) *N
N = N/10
DATA(K+1) = N
PRNT(K+2) = ALPH(DATA(K+2)+1)
PRNT(K+1) = ALPH(DATA(K+1)+1)
ELSE
PRNT(K+2) = ALPH(N+1)
END IF
RETURN
END

The second example shows how alternate returns can be included in a
subroutine.

5-26

Control Statements

SUBROUTINE CHECK(X ,Y. * .* ,C)

50
60
70
80

IF (Z) 60,70 ,80
RETURN
RETURN 1
RETURN 2
END

Depending on the computed value of Z, one of the following returns
occurs:
•

If Z is less than zero, a normal return occurs and the calling program
continues at the first executable statement following CALL CHECK.

•

If Z equals zero, the first alternate return (RETURN 1) occurs.

•

If Z is greater than zero, the second alternate return (RETURN 2)
occurs.

Control returns to the statement specified as the first or second alternate
return argument in the CALL statement argument list; for example, the
CALL statement might take the following form:
CALL CHECK(A,B,*10, *20 ,C)

In this case, RETURN 1 transfers control to statement label 10 and
RETURN 2 transfers control to statement label 20.
If a subroutine includes an alternate return specifying a value less than 1
or greater than the number of alternate return arguments, control returns
to the next executable statement after the CALL statement (alternate
returns are ignored). Thus, you should ensure that the value of i is within
the range of alternate return arguments .

5.10 STOP Statement
The STOP statement terminates program execution. It takes the following
form:
STOP [<lisp]

Control Statements

5-27

disp
Is a character constant or a string of decimal numbers (one to five digits).

The disp argument is optional. If you specify it, the STOP statement displays the contents of <lisp at your terminal, terminates program execution,
and returns control to the operating system. If you do not specify a value
for disp, the following message is sent by the system:
FORTRAN STOP

Examples

The following examples demonstrate valid STOP statements:
STOP 98
STOP 'END OF RUN'

5-28 Control Statements

Chapter 6

Subprograms - Subroutines and
Functions
Subprograms are program units that can be invoked from another program
unit, usually to perform some commonly used computation on behalf
of the other program unit. Normally, the program unit invoking the
subprogram passes values, known as actual arguments, to the subprogram,
which uses the actual arguments to compute the results and then returns
the results to the calling program.
Subprograms are either written by the user or supplied as part of the VAX
FORTRAN library.
User-written subprograms include the following:

•

Statement functions-A computing procedure defined by a single
statement that is similar in form to an assignment statement. A
statement function is invoked by a function reference in a main
program unit or a subprogram unit.
Function subprograms-Program units, also called functions, that contain a set of commonly used computations. A function subprogram's
first statement is a FUNCTION statement, optionally preceded by an
OPTIONS statement A function subprogram is invoked by a function
reference in a main program unit or a subprogram unit.
Subroutine subprograms-Program units, also called subroutines,
that contain a set of commonly used computations. A subroutine
subprogram's first statement is a SUBROUTINE statement, optionally
preceded by an OPTIONS statement A subroutine subprogram
receives control when it is invoked with a CALL statement and
returns control with a RETURN statement.

Subprograms -

Subroutines and Functions

6-1

Subprograms supplied as part of the FORTRAN library are called intrinsic

functions and include the following categories:
•
•
•

6.1

Mathematical
Character-handling
Lexical-comparison

Subprogram Arguments
Subprogram arguments are either dummy arguments or actual arguments:
•
•

Dummy arguments are specified when you write the subprogram.
Actual arguments are specified when you invoke the subprogram.

When control is transferred to a subprogram, each dummy argument takes
the value of the corresponding actual argument. When control is returned
to the calling program unit, the last value assigned to a dummy argument
is assigned to the corresponding actual argument.
Section 6.1 .1 describes the general techniques used to pass arguments
between FORTRAN programs. Section 6.1.2 describes how to use built-in
functions, supplied by VAX FORTRAN, to pass arguments between VAX
FORTRAN subprograms and subprograms written in other languages.

6.1.1

Actual Argument and Dummy Argument Association
Actual arguments must agree in order, number, and data type (or structure, for record arguments) with their corresponding dummy arguments.
Actual arguments can be scalar references, array name references, aggregate references, alternate return specifiers, or subprogram names. The
dummy arguments specified in subprogram definitions, representing
corresponding actual arguments, appear as unsubscripted names.
Although dummy arguments are not actual variables, arrays, records, or
subprograms, each dummy argument can be declared as though it were a
variable, array, record, or subprogram.

•

6-2

Subprograms -

A dummy argument declared as an array can be associated only with
an actual argument that is an array or array element of the same
data type. The actual argument must not be placed in parentheses.
If a dummy argument is an array, it must be no larger than the
Subroutines and Functions

•

array that is the actual argument. You can use adjustable arrays
(see Section 6.1.1.1) to process arrays of different sizes in a single
subprogram .
A dummy argument declared as a record can be associated only with
an actual argument that is an aggregate reference for an entity with a
matching structure .
A dummy argument referenced as a subprogram must be associated with an actual argument that has been declared EXTERNAL or
INTRINSIC in the calling routine.

The length of a dummy argument with a data type of character must
not be greater than the length of its associated actual argument. If the
character dummy argument's length is specified as •(•), it uses the length
of the associated actual argument. (This is known as a passed-length
character argument. See Section 6.1.1.3.)
The following sections discuss several kinds of arguments:
•
•
•
•
•
6. 1 . 1 . 1

Adjustable array
Assumed-size array
Passed-length character
Character and Hollerith constant
Alternate return

Adjustable Arrays

Adjustable arrays are dummy arguments in subprograms. The dimensions
of an adjustable array are determined in the reference to the subprogram.
The array declarator (see Section 2.2.3.1) for an adjustable array can
contain integer variables that are either dummy arguments or variables in
a common block.
When the subprogram is entered, each dummy argument used in the array
declarator must be associated with an actual argument, and each variable
in a common block used in an array declarator must have a defined value.
The dimension declarator is evaluated using the values of the actual
arguments, variables in common blocks, and constants specified in the
array declarator.
Argument association is not retained between one reference to a subprogram and the next reference to that subprogram.
The size of the adjustable array must be less than or equal to the size of
the array that is its corresponding actual argument.
Subprograms - Subroutines and Functions

6-3

Examples

The following examples demonstrate valid and invalid adjustable arrays:

Valid
In the first example, the function computes the sum of the elements of
a two-dimensional array. Notice how the dummy arguments Mand N
control the iteration.

FUNCTION SUM(A,M,N)
DIMENSION A(M,N)
SUM = 0 .0
DO 10 J=1,N
DO 10 I=l,M
SUM= SUM+ A(I,J)
RETURN
END

The following statements are sample calls on SUM:
DIMENSION A1(10 ,35) , A2(3,56)
SUM1 = SUM(Al , 10,35)
SUM2 = SUM(A2,3,56)
SUM3 = SUM(Al,10,10)

An adjustable array is undefined if a dummy argument array is not
currently associated with an actual argument array. It is also undefined
if any of the variables in the adjustable array declarator are either not
currently associated with an actual argument or not in a common block.
The subroutine subprogram in the next example includes statements of
a calling program unit. It illustrates how argument association is not
retained between one reference to a subprogram and the next reference.
SUBROUTINE S(A,I,X)
DIMENSION A(I)
A(I) = X
RETURN
ENTRY S1(I,A ,K, L)
A(I) = A(I) + 1 .0
RETURN
END

The following program unit calls the subroutine subprogram from the
previous example. This calling program unit defines B as a real array
with 10 elements. The first call to subroutine S sets array element B(2)
equal to the value 3.0. The second call to subroutine S (at entry point Sl)
increments array element B(S) by the value 1.0. RECORD statements not
contained within structure declaration blocks can also declare adjustable
arrays .

6-4 Subprograms - Subroutines and Functions

DIMENSION B(10)

CALL S(B ,2 ,3 .0)

CALL S1(5 ,B,3,2)

The upper- and lower-dimension bound values are determined once each
time a subprogram is entered. These values do not change during the execution of that subprogram even if the values of variables contained in the
array declaration are changed. In the next example, the adjustable array X
is declared as X(-4:4,5) on entry to subroutine SUB. The assignments to I
and J do not affect that declaration.
DIMENSION ARRAY(9 ,5)
L = 9

M= 5
CALL SUB(ARRAY , L, M)
END

SUBROUTINE SUB(X,I , J)
DIMENSION X( - I/2 : I/2,J)
X(I/2.J) = 999
J = 1

END

Invalid
The following example is invalid-once a variable is used in an array
declarator for an adjustable array, it must not appear in a type declaration
that changes the variable's da,ta type.
SUBROUTI NE SUB1(A,X)
DIMENSION A(X)
INTEGER X

Subprograms -

Subroutines and Functions

6-5

6.1.1.2

Assumed-Size Arrays

An assumed-size array is a dummy array for which the upper bound of
the last dimension is specified as an asterisk (•), for example:
SUBROUTINE SUB(A,N)
DIMENSION A(1 :N,1 :*)

The size of an assumed-size array and the number of elements that can be
referenced are determined as follows:
•

•

If the actual argument corresponding to the dummy array is a name

of a noncharacter array, the size of the dummy array is the size of the
actual-argument array.
If the actual argument corresponding to the dummy argument is a
name of a noncharacter array element, with a subscript value of s in
an array of size a, the size of the dummy array is a+ 1 - s.
If the actual argument is a name of a character array, character array
element, or character array element substring and begins at character
storage unit b of an array with n character storage units, the size of
the dummy array is INT(n + 1- b)/y, where y is the length of an
element of the dummy array.

Because the actual size of an assumed-size array is unknown, an assumedsize array name cannot be used as any of the following items in an 1/0
statement:
•
•
•

Array name in the 1/0 list
Unit identifier for an internal file
Run-time format specifier

RECORD statements not contained within structure declaration blocks can
also declare adjustable arrays..

6-6

Subprograms -

Subroutines and Functions

6.1.1.3

Passed-Length Character Arguments

A passed-length character argument is a dummy argument that assumes
the length attribute of the corresponding actual argument. An asterisk is
used to specify the length of the dummy character argument.
When control transfers to the subprogram, each dummy argument assumes the length of its corresponding actual argument.
A character array dummy argument can also have a passed length.
The length of each element in the dummy argument is the length of
the elements in the actual argument. The passed length and the array
declarator together determine the size of the passed-length character array.
A passed-length character array can also be an adjustable or assumed-size
array.
Examples

The following example of a function subprogram uses a passed-length
character argument. The function finds the position of the character with
the highest ASCII code value. It uses the length of the passed-length
character argument to control the iteration.
(The processor-defined function LEN determines the length of the argument. See Section 6.3.2.1 for a description of the LEN function.)

INTEGER FUNCTION lCMAX(CVAR)
CHARACTER*(*) CVAR
ICMAX = 1
DO 10 I=2,LEN(CVAR)
IF (CVAR(I :l) . GT . CVAR(lCMAX : ICMAX)) ICMAX=I
RETURN
END

The length of the dummy argument is determined each time control
transfers to the function . The length of the actual argument can be the
length of a character variable, array element, substring, or expression.
Each of the following function references specifies a different length for
the dummy argument:
CHARACTER VAR*10 , CARRAY(3 ,5) *20

I1 = ICMAX(VAR)
I2 = ICMAX(CARRAY(2 , 2))
I3 = ICMAX(VAR(3 :8))
14 = ICMAX(CARRAY(l,3)(5 :15))
15 = ICMAX(VAR(3 :4)//CARRAY(3 , 5))

Subprograms -

Subroutines and Functions

6-7

6. 1. 1.4

Character and Hollerith Constants as Actual Arguments

Actual arguments and their corresponding dummy arguments must agree
in data type. If the actual argument is a Hollerith constant (for example,
4HABCD), the dummy argument must be of numeric data type. In VAX
FORTRAN, if an actual argument is a character constant (for example,
'ABCD'), the corresponding dummy argument can have either a numeric
or a character data type. If the dummy argument has a numeric data
type, the character constant 'ABCD' is, in effect, converted to a Hollerith
constant by the FORTRAN compiler and the linker.
An exception to this occurs when the function or subroutine name is itself
a dummy argument. It is not possible to determine at compile time or link
time whether a character constant or Hollerith constant is required. In
this case, a character constant actual argument can correspond only to a
character dummy argument.
Example

The following example shows character and Hollerith constants being used
as actual arguments. In this example, the subroutine names CHARSUB
and HOLLSUB are themselves dummy arguments of the subroutine S.
Therefore, the actual argument 'STRING' in the call to CHARSUB must
correspond to a character dummy argument, whereas th e actual argument
6HSTRING in the call to HOLLSUB must correspond to a Hollerith
dummy argument
SUBROUTINE S(CHARSUB,HOLLSUB , A,B)
EXTERNAL CHARSUB ,HOLLSUB

CALL CHARSUB(A , 'STRI NG')
CALL HOLLSUB(B, 6HSTRI NQ

6-8

Subprograms -

Subroutines and Functions

6.1.1.5

Alternate Return Arguments

To specify an alternate return argument in a dummy argument list, place
asterisks in the list; for example:
SUBROUTr'NE MINN (A, B, * ,

* ,C)

The actual argument list passed in the CALL statement must include alternate return arguments in the corresponding positions. These arguments
take either one of the following forms:
*label
&l abe l

Either an asterisk or an ampersand can indicate an alternate return argument in an actual argument list. The value you specify for label must be
the label of an executable statement in the program unit that issues the
CALL statement.

6.1.2

Built-In Functions
Built-in functions perform utility operations that are useful in communicating with subprograms written in languages other than FORTRAN. VAX
FO RTRAN provides the following built-in functions:

6.1.2.1

•

Argument list

•

%LOC

Argument List Built- In Functions

To call subprograms (such as VAX/VMS system services) written in lan guages other than FORTRAN, you may need to pass th e actual arguments
in a form different from that used by FORTRAN .
To change the form of the argument, you can use the following built-in
functions in the argumen t list of a CALL statement or fun ction reference:
%VAL, %REF, %DESCR.
These built-in functions specify the way the argument should be passed to
the subprogram. You can use them only in the actual argument list of a
CALL statement or func tion reference-and in no other context.

Subprograms -

Subroutines and Functions

6-9

The three argument list built-in functions have the following effects:
Function

Effect

%VAL(a)

Pass the argument as a 32-bit immediate value. (If the actual
argument is shorter than 32 bits, it is sign-extended to a 32-bit
value.)

%REF(a)

Pass the argument by reference.

%DESCR(a)

Pass the argument by descriptor.

a is an actual argument.

See the VAX FORTRAN User Manual for more information on argumentpassing mechanisms.
Table 6-1 lists the FORTRAN argument-passing defaults and the allowed
uses of %VAL, %REF, and %DESCR.
Table 6-1:

Argument List Built-In Functions and Defaults
Allowed Functions

Actual Argument
Data Type

Default

%VAL

%REF

%DESCR

REF

Yes 1

Yes

Integer

REF

Yes

REAL•4

REF

Yes

REAL•8

REF

Yes

REAL•16

REF

Yes

Complex

REF

Yes

Character

DESCR

Yes

Hollerith

REF

Aggregate

REF

Yes

REF

Yes

Expressions
Logical

Array Name
Numeric
1

If a logical or integer value occupies less than 32 bits of storage, it is con verted to a
32 -bit value by sign extension . Use the ZEXT function if zero extension is desired .

6-1 0 Subprograms - Subroutines and Functions

Table 6 - 1 (Cont.) :

A rgument List Built-In Functions and
Def aults
Allowed Functions

Actual Argument
Data Type

Default

%VAL

%REF

%DESCR

Character

DESCR

Yes

Aggregate

REF

No
No

Yes

Procedure Name

6.1.2 .2

N u m e ric

REF

Character

DESCR

No
No

%LOC Built-In Function

The %LOC built-in function computes the internal address of a storage
element. It takes the following form :
%LOC( arg )

arg
Is a scalar memory reference, array name reference, aggregate reference,
or external procedure name.
The %LOC built-in function produces an INTEGER*4 value that represents the location of its argument. The INTEGER* 4 value can be used as
an element in an arithmetic expression.
See th e VAX FORTRAN User Ma nua l for more information on the %LOC
built-in function.

6.2

User-Written Subprograms
A user-written subprogram is a FORTRAN statement or group of
FORTRAN statements that performs a computing procedure. The computing procedure can be either a series of arithmetic operations or a series
of FORTRAN statements. A single subprogram can perform a computing
procedure in several places in your program, and thus avoid duplicating a
series of operations or statements in each place.

Subprograms -

Subroutines and Functions

6-11

There are three types of subprograms. Table 6-2 lists each type of subprogram, the statements needed to define the subprogram, and the method of
transferring control to it.
Table 6-2: Types of User-Written Subprograms
Control Transfer Method
Subprogram Type
Defining Statements
Statement function

Statement function
definition

Function reference

Function

FUNCTION
ENTRY

Function reference

Subroutine

SUBROUTINE
ENTRY

CALL statement

A function reference is used in an expression and consists of the function
name and the function arguments. A function reference returns a value
that is used in evaluating the expression in which the function appears.
Function and subroutine subprograms can change the values of their
arguments, and the calling program can use the changed values.
A subprogram can refer to other subprograms, but it cannot refer to itself,
either directly or indirectly.

6.2. 1

Statement Functions
A statement function is a computing procedure defined in the same
program unit in which it is referenced. It is defined by a single statement
that is similar in form to an assignment statement. The computation is
performed each time you refer to the statement function. The resulting
value is then made available to the expression that contains the statement
function reference.
Statement function definitions take the following form:
fun ( [p [. p] ... ]) = e

fun
Is the symbolic name of the statement function.
p
Is a dummy argument.

6-12

Subprograms -

Subroutines and Functions

e
Is an arithmetic, logical, or character expression that defines the computation to be preformed.
Statement function references take the following form :
f( [p [. p] . .. ])

Is the symbolic name of the statement function .
p

Is an actual argument.
Syntax Rules

The following rules apply to statement function definitions and references:
•

•

When a statement function reference appears in an expression, the
values of the actual arguments are associated with the dummy arguments in the statement function definition . The expression in the
definition is then evaluated. The resulting value is used to complete
the evaluation of the expression containing the function reference.
The data type of a statement function is determined either implicitly
by the initial letter of the function name, or explicitly in a type
declaration statement. The data type can be any of the data types,
including the character data type.
Dummy arguments in a statement function indicate only the number,
order, and data type of the actual arguments. The names of the
dummy arguments can represent other entities elsewhere in the
program unit.
Except for the data type, declarative information associated with an
entity is not associated with dummy arguments in the statement
function: declaring an entity to be an array or to be in a common
block does not affect a dummy argument with the same name.
Actual arguments must agree in number, order, and data type with
their corresponding dummy arguments.

Subprograms -

Subroutines and Functions

6-13

•
•

The name of the statement function cannot represent any other entity
within the same program unit.
The expression in a statement function definition can contain function
references. If a reference to another statement function appears in the
expression, it must be previously defined in the same program unit.
Any reference to a statement function must appear in the same
program unit as the definition of that function.
A statement function reference must appear as, or be part of, an
expression. The reference cannot appear on the left side of an assignment statement.

Examples

The following statement function definitions are valid:
VOLUME(RADIUS) = 4.189*RADIUS **3
SI NH(X) = (EXP(X)-EXP( - X)) *0.5
CHARACTER*10 CSF,A , B
CSF(A,B) = A(6 : 10)//B(1 :5)

The following statement function definition is invalid because it contains a
constant, which cannot be used as a dummy argument:
AVG(A,B,C,3 . ) = (A+B+C)/3 .

Consider the following definition:
AVG(A,B,C) = (A+B+C)/3 .

Based on the previous statement, the following references are valid:

GRADE= AVG(TEST1 , TEST2,XLAB)
IF (AVG(P ,D,Q) .LT . AVG(X ,Y,Z)) GO TO 300

The following reference is invalid because the data type of the third
argument does not agree with the dummy argument:
FINAL= AVG(TEST3,TEST4,LAB2)

6-14 Subprograms - Subroutines and Functions

8.2.2

Function Subprograms
A function subprogram is a program unit consisting of a FUNCTION
statement followed by a series of statements that define a computing
procedure. Function references transfer control to a function subprogram;
RETURN or END statements return control to the calling program unit.
A function subprogram returns a single value to the calling program unit
by assigning that value to the function 's name. The function's name
determines the data type of the value returned.

6.2.2. 1

Logical and Numeric Functions

The FUNCTION statement takes the following form:
[typ] FUNCTION nam [ *m] [ ( [p [. p] . . . ]) ]

typ
Is one of the logical or numeric data type specifiers. See Section 4.4.1 for
a list of these specifiers.
nam

Is the symbolic name of the function .
m

Is an unsigned, nonzero integer constant specifying the length of the data
type. It must be one of the valid length specifiers for the data type given
by typ.
p

Is a dummy argument.
6.2.2.2

Character Functions

The CHARACTER FUNCTION statement takes the following form :
CHARACTER [ *n] FUNCTION nam : *n]

[ ( [p [ , p] .. . ] ) ]

Subprograms - Subroutines and Functions

6-15

n
Is an unsigned, nonzero integer constant, or parenthetical asterisk indicating a passed-length function name.
If you specify CHARACTER*(*), the function assumes the length declared
for it in the program unit that invokes it. A passed-length character function can have different lengths when it is invoked by different program
units. If n is an integer constant, the value of n must agree with the length
of the function specified in the program unit that invokes the function. If
you do not specify n, a length of one is assumed. If the length has already
been specified following the keyword CHARACTER, the optional length
specification following nam is not permitted .
nam
Is the symbolic name of the function.
p
Is a dummy argument.

6.2.2.3

Function Reference

A function reference that transfers control to a function subprogram takes
the following form :
nam ( [p [, p] . . . ])

nam
Is the symbolic name of the function.
p
Is an actual argument.

When control transfers to a function subprogram, the values of any actual arguments in the function reference are associated with any dummy
arguments in the FUNCTION statement. The statements in the subprogram are then executed. The resulting value is assigned to the name of
the function. Finally, the function returns control to the calling program
unit. The value assigned to the function's name is now available to the
expression containing the function reference and is used to complete the
evaluation of that expression.

6-16

Subprograms -

Subroutines and Functions

The data type of a function name can be specified explicitly in the
FUNCTION statement or in a type declaration statement; it can also
be specified implicitly. The function name defined in the function subprogram must have the same data type as the function name in the calling
program unit.
The FUNCTION statement must be the first statement of a function subprogram, unless an OPTIONS statement is used . A function subprogram
cannot contain a SUBROUTINE statement, a BLOCK DATA statement, a
PROGRAM statement, or another FUNCTION statement. ENTRY statements can be included to provide multiple entry points to the subprogram
(see Section 6.2.4).

Examples
Consider the following example:
FUNCTION ROOT (A)

x = 1 .0

EX = EXP(X)
EMINX = 1 . /EX
ROOT= ((EX+EMINX) *. 5+COS(X)-A)/ ( (EX-EMI NX) * .5-SIN(X))
IF (ABS(X-ROOT) .LT . 1E-6) RETURN
X = ROOT
GO TD 2

END

To obtain the root of the function, the previous example uses the NewtonRaphson iteration method:

F (X) = cosh(X) + cos( X) - A = 0
The value of A is passed as an argument. The iteration formula for this
root is as follows:

X·
i+l

= X · _ cosh(Xi) + cos( X i) - A
i

sinh(Xi) - sin(Xi)

This formula is calculated repeatedly until the difference between Xi
and Xi+l is less than 1.0E-6. The function uses the FORTRAN intrinsic
functions EXP, SIN, COS, and ABS (see Section 6.3).

Subprograms -

Subroutines and Functions

6-17

The next example is a passed-length character function. It returns the
value of its argument, repeated to fill the length of the function.
CHARACTER*( *) FUNCTION REPEAT(CARG)
CHARACTER*! CARG
DO 10 I=1,LEN(REPEAT)
REPEAT(I : I) = CARG
RETURN
END

Within any given program unit all references to a passed-length character
function must have the same length. In the following example, the
REPEAT function has a length of 1000:
CHARACTER*1000 REPEAT, MANYAS, MANYZS
MANYAS = REPEAT('A')
MANYZS = REPEAT('Z')

Another program unit within the executable program can specify a different length. In the following example, the REPEAT function has a length
of 2:
CHARACTER HOLD*6. REPEAT*2
HOLD= REPEAT('A')//REPEAT('B')//REPEAT('C')

6.2.3

Subroutine Subprograms - SUBROUTINE Statement
A subroutine subprogram is a program unit consisting of a SUBROUTINE
statement followed by a series of statements that define a computing procedure. The CALL statement transfers control to a subroutine subprogram;
a RETURN or END statement returns control to the calling program unit.
SUBROUTINE statements take the following form:
SUBROUTINE sub [([p[,p] . . . ])]

sub

Is the symbolic name of the subroutine.
p

Is a dummy argument. An asterisk in the argument list specifies a dummy
argument as an alternate return argument.
When control transfers to the subroutine, the values of any actual arguments in the CALL statement are associated with any corresponding
dummy arguments in the SUBROUTINE statement. The statements in
the subprogram are then executed. (Section 5.1 describes the CALL
statement.)
6-18 Subprograms - Subroutines and Functions

The SUBROUTINE statement must be the first statement of a subroutine,
unless an OPTIONS statement is used.
A subroutine subprogram cannot contain a FUNCTION statement,
a BLOCK DATA statement, a PROGRAM statement, or another
SUBROUTINE statement. ENTRY statements are allowed to specify
multiple entry points in the subroutine (see Section 6.2.4).
Examples

The first example contains a subroutine that computes the volume of a
regular polyhedron, given the number of faces and the length of one
edge. It uses the computed GO TO statement to determine whether
the polyhedron is a tetrahedron, cube, octahedron, dodecahedron, or
icosahedron. The GO TO statement also transfers control to the proper
procedure for calculating the volume. If the number of faces is not 4, 6, 8,
12, or 20, the subroutine sends an error message to the terminal.
Main Program

COMMON NFACES, EDGE, VOLUME
ACCEPT*· NFACES, EDGE
CALL PLYVOL
TYPE*· 'VOLUME=', VOLUME
STOP
END

Subprograms - Subroutines and Functions

6-19

Subroutine

1
2
3
4
5
6
100

SUBROUTINE PLYVOL
COMMON NFACES, EDGE , VOLUME
CUBED = EDGE**3
GO TO (6,6,6 , 1,6,2,6,3,6,6 ,6,4,6,6,6,6 ,6 ,6,6,5), NFACES
GO TO 6
VOLUME= CUBED* 0 . 11785
RETURN
VOLUME = CUBED
RETURN
VOLUME= CUBED * 0 . 47140
RETURN
VOLUME = CUBED * 7.66312
RETURN
VOLUME = CUBED * 2 . 18170
RETURN
TYPE 100, NFACES
FORMAT (I NO REGULAR POLYHEDRON HAS I . 13. I FACES . I/)
VOLUME = 0.0
RETURN
END

The next example uses alternate return specifiers to determine where
control transfers on completion of the subroutine. The SUBROUTINE
statement argument list contains two dummy alternate return arguments
corresponding to the actual arguments •10 and •20 in the CALL statement
argument list.
The decision about which RETURN statement executes depends on the
value of Z, as computed in the subroutine:
•

If Z is less than zero, the normal return executes.

•

If Z is equal to zero, the return is to statement label 10 in the main
program.

•

If Z is greater than zero, the return is to statement label 20 in the main
program.

6-20 Subprograms - Subroutines and Functions

Main Program

Subroutine

CALL CHECK(A,B.*10, *20 ,C)
TYPE * · 'VALUE LESS THAN ZERO'
GO TO 30
10 TYPE*. 'VALUE EQUALS ZERO'
GO TO 30
20 TYPE*, 'VALUE MORE THAN ZERO'
30 CONTINUE

6.2.4

SUBROUTINE CHECK(X,Y , *. * .Q)

50 IF (Z) 60,70,80
60 RETURN
70 RETURN 1
80 RETURN 2
END

ENTRY Statement
The ENTRY statement provides multiple entry points within a subprogram. It is not executable and can appear within a function or subroutine
program after the FUNCTION or SUBROUTINE statement. Execution of a
subprogram referred to by an entry name begins with the first executable
statement after the ENTRY statement.
The ENTRY statement takes the following form:
ENTRY nam [ ( [p [ , p] . . . ]) ]

nam
Is the symbolic name of an entry point.
p
Is a dummy argument.
Syntax Rules

The following rules apply to ENTRY statements and names:
•
•
•

CALL statements should be used to refer to entry names within
subroutine subprograms.
Function references should be used to refer to entry names within
function subprograms.
An entry name within a function subprogram can appear in a type
declaration statement.

Subprograms -

Subroutines and Functions

6-21

•
•
•

•

6.2.4.1

An EXTERNAL statement can specify an entry name and use it as an
actual argument-but not as a dummy argument.
Entry names cannot appear in executable statements that physically
precede their appearance in an ENTRY statement.
Alternate return arguments can be included in ENTRY statements if
they have asterisks in the dummy argument list. ENTRY statements
that specify alternate return arguments can be used only in subroutine
subprograms.
Dummy arguments can be used in ENTRY statements even if they
differ in order, number, type, and name from the dummy arguments
used in the FUNCTION, SUBROUTINE, and other ENTRY statements
in the same subprogram. However, each reference to a function,
subroutine, or entry must use an actual argument list that agrees
in order, number, and type with the dummy argument list in the
corresponding FUNCTION, SUBROUTINE, or ENTRY statement.
Dummy arguments can be referred to only in executable statements
that follow the first SUBROUTINE, FUNCTION, or ENTRY statement
in which the dummy argument is specified. If a dummy argument
is not currently associated with an actual argument, the dummy
argument is undefined and cannot be referenced-arguments do not
retain their association from one reference of a subprogram to another.
ENTRY statements cannot appear within a block IF construct or a DO
loop.

ENTRY Statements in Function Subprograms

All entry names within a function subprogram are associated with the
name of the function subprogram. Therefore, defining any entry name
or the name of the function subprogram defines all the associated names
with the same data type. All associated names with different data types
become undefined.
The function and entry names do not need to have the same data type,
but they all must be consistent within one of the following groups of data
types:
Group 1:

BYTE, INTEGER•2, INTEGER•4, LOGICA L•2, LOGICAL•4 ,
REAL•4, REAL•8, COMPLEX•8

Group 2:

COMPLEX•16, REAL•16

Group 3:

CHARACTER

6-22 Subprograms - Subroutines and Functions

When either a RETURN statement or an implied return at the end of a
subprogram is executed, the symbolic name used to refer to the function
subprogram must be defined.
If the function has a character data type, all entry names must have a
character data type and the same length specification as the function . The
specified length must also agree with the length specified in the program
unit referring to the entry name. If an asterisk enclosed in parentheses is
used to specify the length of the entry name, the entry name has a passed
length (see Section 6.1.1.3 and the VAX FORTRAN User Manual) .

Example

The following example illustrates a function subprogram that computes
the hyperbolic functions sinh, cosh, and tanh:
REAL FUNCTION TANH(X)
C

Statement function to compute twice sinh

TSINH(Y) = EXP(Y) - EXP(-Y)
C

Statement function to compute twice cash

TCOSH(Y) = EXP(Y)
C

EXP(-Y)

Compute tanh

TANH = TSI NH(X)/TCOSH(X)
RETURN
C

Compute sinh

ENTRY SINH(X)
SI NH = TSINH(X)/2 .0
RETURN
C

Compute cash

ENTRY COSH(X)
COSH = TCOSH(X)/2 .0
RETURN
END

Subprograms - Subroutines and Functions

6-23

6.2.4.2

ENTRY Statements in Subroutine Subprograms

To refer to an entry point name in a subroutine, you should issue a
CALL statement that includes the entry point name defined in the ENTRY
statement. In the following example, the call is to an entry point (SUBA)
within the subroutine (SUB). Execution begins with the first statement
following ENTRY SUBA (Q,R,S), using the actual arguments (A,B,C)
passed in the CALL statement.
Main Program

Subroutine

CALL SUBA(A,B,C)

SUBROUTINE SUB(X,Y,Z)

ENTRY SUBA(Q,R,S)

Alternate returns can be specified in ENTRY statements, for example:
SUBROUTINE SUB(K,*.*)

ENTRY SUBC(J ,K, *.*,X)

RETURN 1
RETURN 2
END

If you issue a call to entry point SUBC, you must include actual alternate
return arguments, for example:
CALL SUBC(M,N,*100,*200,P)

In this case, the RETURN 1 statement transfers control to statement label
100 and the RETURN 2 statement transfers control to statement label 200
in the calling program.

6-24 Subprograms - Subroutines and Functions

6.3 FORTRAN Intrinsic Functions
FORTRAN intrinsic functions perform frequently used mathematical
computations. They are supplied in the VAX FORTRAN library.
References to FORTRAN intrinsic functions use the same form as references to user-defined functions. For example, the following intrinsic
function reference is valid:
R = 3.14159 * ABS(X-1)

This reference to the intrinsic function ABS causes the absolute value of
X-1 to be multiplied by the constant 3.14159; the result of that calculation
is assigned to the variable R.
Two methods of referencing intrinsic functions are described in the
following sections.
A listing of the intrinsic functions, their data types, and the data type
of their actual arguments is located in Appendix D. Further information
describing intrinsic function algorithms is located in the VMS Run-Time
Library Routines Volume.

6.3.1

Intrinsic Function References
FORTRAN library function names are called intrinsic function names.
Normally, a name in the table of intrinsic function names (Table D-3)
refers to the FORTRAN library function with that name. However, the
name can refer to a user-defined function when the name appears in an
EXTERNAL statement (see Section 4.7).
Except when they are used in an EXTERNAL statement, intrinsic function
names are local to the program unit that refers to them. Thus, they can be
used for other purposes in other program units. In addition, the data type
of an intrinsic function does not change if you use an IMPLICIT statement
to change the implied data type rules.
Intrinsic and user-defined functions cannot have the same name if they
appear in the same program unit.

Subprograms -

Subroutines and Functions

6-25

6.3.1.1

Generic References to Intrinsic Functions

Many of the intrinsic functions supplied with VAX FORTRAN have generic
names, which means that you refer to them by a common name and the
selection of the actual library routine to be used is based on the data type
of the argument in the function reference. For example, there are five
intrinsic functions that calculate cosines. All of them can be referred to
by the generic name COS. Their names are COS, DCOS, QCOS,CCOS,
and CDCOS These functions differ in that they return REAL•4, REAL•8,
REAL*16, COMPLEX•8, and COMPLEX•16 values, respectively.
To invoke the cosine function, you can refer to it generically as COS. The
compiler then selects the appropriate routine, based on the arguments that
you specify. For example, if the argument is REAL•4, COS is selected; if it
is REAL•8, DCOS is selected; and if COMPLEX•8, CCOS is selected.
However, you can explicitly refer to a particular routine if you wish. Thus,
to invoke the double-precision cosine function, you could specify DCOS
rather than use the generic name.
The compiler lists the internal names of the intrinsic functions it has
selected in the "FUNCTIONS AND SUBROUTINES REFERENCED"
section of the source code listing.
Function selection occurs independently for each generic reference . Thus,
you can use a generic reference repeatedly in the same program unit to
access different intrinsic functions.
Table 6-3 lists generic intrinsic function names. However, you cannot use
the names in this table to generically select intrinsic functions if you use
them in any of the following ways:
•
•

As the name of a statement function
As a dummy argument name, a common block name, or a variable or
array name

Using the generic name of an intrinsic function in an INTRINSIC statement (see Section 4. 9) does not affect function references. However, when
you use a generic function name in an actual argument list as the name of
a function to be passed, function selection does not occur because there is
no argument list on which to base a selection. The name is treated according to the rules for handling specific intrinsic function names described in
Section 6.3.

6-26

Subprograms -

Subroutines and Functions

Generic function names are local to the program unit that refers to them.
Thus, they can be used for other purposes in other program units.
Table 6-3:

Summary of Generic Intrinsic Function Names
Data Type of
Data Type of
Generic Name
Argument
Result

ABS

Integer
Real
COMPLEX•8
COMPLEX•1 6

Integer
Real
REAL•4
REAL•8

AINT, ANINT

Real

NINT

Real

Integer

INT

Integer
Real
Complex

Integer
Integer
Integer

REAL

Integer
Real
Complex

REAL•4
REAL•4
REAL•4

DBLE

Integer
Real
Complex

REAL•8
REAL•8
REAL•8

QEXT

In teger
Real
Complex

REAL•16
REAL•1 6
REAL• 16

CMPLX

Integer
Real
Complex

COMPLEX•8
COMPLEX•8
COMPLEX•8

DCMPLX

Integer
Real
Complex

COMPLEX•16
COMPLEX•16
COMPLEX•l6

MOD, MAX, MIN, SIGN, DIM

Integer
Real

EXP, LOG, SIN, COS, SQRT

Real
Complex

LOGlO, SIN O, COSD, TAN,
TAND . ATAN, ATAN D, ATAN2,
ATAN2D, ASIN, ASIN D, ACOS,
ACOSD, SINH, COSH, TANH

Real

Subprograms - Subroutines and Functions

6-27

6.3. 1.2

Using Intrinsic Function Names

Example 6-1 shows the different ways to use intrinsic function names. In
this annotated example, a single executable program uses the name SIN in
four distinct ways:
•
•
•
•

As the name of a statement function
As the generic name of an intrinsic function
As the specific name of an intrinsic function
As the name of a user-defined function

Using the name in these four ways emphasizes the local and global
properties of the name.
Example 6-1:
C

Using Multiple Function Names

Compare ways of computing sine.
PROGRAM SINES
REAL*8 X, PI
PARAMETER (PI=3 . 141592653589793238DO)
COMMON V(3)

Define SIN as a statement function

SIN(X) = COS(PI/2-X)
DO 10 X = -PI, PI, 2*PI/100
CALL COMPUT(X)
C

Reference the statement function SIN

10
100

WRITE (6,100) X, V, SIN(X)
FORMAT (5F10 .7)
END

SUBROUTINE COMPUT(Y)
REAL*8 Y
C

Use intrinsic function SIN as actual argument t)
INTRINSIC SIN
COMMON V(3)

Generic reference to double-precision sine Ct
V(1) = SIN(Y)

Example 6-1 Cont'd. on next page

6-28 Subprograms - Subroutines and Functions

Example 6-1 (Cont.):
C

Using Multiple Function Names

I NTR INSIC FUNCTION SI NE AS ACTUAL ARGUMENT 0
CALL SUB(REAL(Y) ,SI N)
END
SUBROUTI NE SUB(A,S )

Declare SI N as name of user function (!)
EXTERNAL SI N

Declare SI N as type REAL *8 f)
REAL*8 SI N
COMMON V(3)

Evaluate intrinsic funct i on SI N Cal
V(2) = S(A)

Evaluate user-defined SI N function @>
V(3) = SIN(A)
END

Define the user SI N function ~
REAL*8 FUNCTIO N SIN (X)
INTEGER FACTOR
SIN = X - X**3/FACTOR(3) + X**5/FACTOR(5)
1
- X**7/FACTOR(7)
END

I NTEGER FUNCTION FACTOR( N)
FACTOR = 1
DO 10 I= N,1 , -1
FACTOR = FACTOR * I
END

Notes:

A statement function named SIN is defined in terms of the generic
function name COS. Because the argument of COS is double precision,
the double-precision cosine function is evaluated. The statement
function SIN is itself single precision.
The statement function SIN is called.

The name SIN is declared intrinsic so that the single-precision intrinsic
sine function can be passed as an actual argument at 0 .

The generic function name SIN is used to refer to the double-precision
sine function .

Subprograms -

Subroutines and Functions

6-29

The single-precision intrinsic sine function is used as an actual argument.
0 The name SIN is declared a user-defined function name.
0 The type of SIN is declared double precision.
0 The single-precision sine function passed at 0 is evaluated.
0 The user-defined SIN function is evaluated.
G> The user-defined SIN function is defined as a simple Taylor series
using a user-defined function FACTOR to compute the factorial
function.

6.3.2

Character and Lexical Comparison Library Functions
Character library functions take character arguments and return integer,
ASCII, or character values; lexical comparison library functions take
character arguments and return logical values.

6.3.2.1

Character Functions

FORTRAN provides four character functions: LEN, INDEX, !CHAR, and
CHAR.
LEN Function

The LEN function returns the length of a character expression. It takes the
following form:
LEN(c)

c
Is a character expression. The value returned indicates how many bytes
there are in the expression.
The following example uses the LEN function:
SUBROUTINE REVERSE(S)
CHARACTER T, S* (*)
J = LEN(S)
DO 10 I=1,J/2
T = S(I : I)
S(I:I) = S(J : J)
S(J : J) = T
J

6-30

Subprograms -

=J - 1

CONTINUE
RETURN
END

Subroutines and Functions

INDEX Function

The INDEX function searches for a substring (c2) in a specified character
string (cl) and, if it finds the substring, returns the substring' s starting
position. If c2 occurs more than once in cl, the starting position of the
first (leftmost) occurrence is returned. If c2 does not occur in cl, the value
zero is returned. INDEX takes the following form:
I NDEX(c1 ,c2)

c1
Is a character expression specifying the string to be searched for the
substring specified by c2 .

c2
Is a character expression specifying the substring for which the starting
location is to be determined.
The following example uses the INDEX function:
SUBROUTINE FIND_SUBSTRI NGS(SUB,S)
CHARACTER*(*) SUB, S
CHARACTER*132 MARKS
I = 1

MARKS =
10

J = I NDEX(S(I : ) , SUB)
IF (J .NE. 0) THEN
I = I + (J-1)

MARKS(I : I) = 1 # 1
I

=I + 1

IF (I . LE . LEN(S)) GO TO 10
END IF
91

WRITE (6 ,91) S, MARKS
FORMAT (2(/1X,A))
END

ICHAR Function

The ICHAR function converts a character expression to its equivalent
ASCII code and returns the ASCII value. It takes the following form:
!CHAR (c)

Subprograms - Subroutines and Functions

6-31

c
Is the character to be converted to an ASCII code. If c is longer than one
byte, only the value of the first byte is returned; the remainder is ignored.
CHAR Function

The CHAR function converts an ASCII integer value to a character value
and returns the character value. It takes the following form:
CHAR (i)
I

Is an integer expression.
6.3.2.2

Lexical Comparison Functions

FORTRAN provides four lexical comparison functions:
•
•

LLT, where LLT(X,Y) is equivalent to (X .LT. Y)
LLE, where LLE(X,Y) is equivalent to (X .LE. Y)

•
•

LGT, where LGT(X,Y) is equivalent to (X .GT. Y)
LGE, where LGE(X,Y) is equivalent to (X .GE. Y)

Lexical functions take the following form:
func(c,c)

func

Is one of the symbolic names: LLT, LLE, LGT, or LGE.

c
Is a character expression.
The lexical comparison functions defined by the FORTRAN-77 standard
are guaranteed to make comparisons according to the ASCII collating
sequence, even on non-ASCII processors. On VAX systems, the lexical comparison functions are identical to the corresponding character
relationals.

6-32 Subprograms - Subroutines and Functions

Example

The following example illustrates a valid lexical comparison function:
CHARACTER*10 CH2
IF (LGT(CH2, 'SMITH')) STOP

The IF statement in the example is equivalent to the following IF statement:
IF (CH2 .GT . 'SMITH') STOP

Subprograms - Subroutines and Functions

6-33

Chapter 7

1/0 Statements
The following VAX FORTRAN I/O (input/ output) statements initiate data
transfer operations:
•

READ

•

WRITE

•
•
•

REWRITE
ACCEPT
TYPE and PRINT

Following a discussion of the basic components of complete I/O statements, this chapter discusses individual I/O statements. For information
on other statements that influence data transfer operations, but do not
directly initiate them, see Chapters 8 and 9.

7 .1

Components of 1/0 Statements
I/O statements have three basic components: the statement keyword, the
control list, and the I/0 list. The I/O statement keywords specifically
control either input or output operations, as follows:

1/0 Statements 7-1

Input Operations

Output Operations

READ
ACCEPT

WRITE
REWRITE
TYPE
PRINT

The control list and 1/0 list are described separately in the next two
sections.

7. 1. 1 Control List
The control list is composed of one or more parameters that specify the
following:
•
•

•

Logical unit to be acted upon
Internal file to be acted upon
Whether formatting is to be used for data editing, and if it is, the
format specification
NAMELIST group-name specification

•
•

Number of a direct access record to be accessed
Key and key-of-reference of a keyed access record to be accessed

•

Name of the variable that contains the completion status of an 1/0
operation
Label of the statement that receives control if an error or end-of-file
condition occurs

•

The type of a statement can always be determined by the contents of its
control list. For example, the control list of a formatted 1/0 statement
always contains a format specifier (FMT=f or f), whereas that of a listdirected 1/0 statement always contains an asterisk in place of a format
specifier.

7-2

1/0 Statements

The control list takes the following form:
(p[,p] . .. )

p
Is a specifier taking the following form:
[keyword=] value
Is one of several possible keywords and values that are described in
the following sections.

7. 1. 1. 1

Syntax Rules for Control-List Parameters

In VAX FORTRAN I/O statements, control-list parameters have three
different forms (keyword, nonkeyword, and mixed) with the following
syntax rules:

•

Keyword Form: When the control list parameter is specified with a
keyword and equal sign, control-list parameters can appear in any
order in the control list.
Nonkeyword Form: When the control-list parameter is specified without
a keyword or equal sign, either the logical unit specifier or the internal
file specifier must occupy the first (leftmost) position in the control list.
The nonkeyword form of the direct-access record specifier must
immediately follow the nonkeyword form of the logical unit specifier.
When used with a logical unit specifier or internal file specifier, the
nonkeyword form of the formator namelist specifier must occupy the
second position in the control list. The unit or internal file specifier
must also be in nonkeyword form (and thus occupy the first position
in the control list).

•

7 .1.1.2

Mixed Forms: When keyword and nonkeyword forms are mixed in the
same 1/0 statement, nonkeyword rules apply to the control list.

Logical Unit Specifier

The logical unit specifier identifies the logical unit to be accessed. It takes
either one of the following forms:
[UNIT= Ju
[UNIT=]*

1/0 Statements

7-3

u
Is an integer expression with a value in the range 0 through 99 that refers
to a specific file or I/O device. If necessary., the value is converted to
integer data type before use.

Specifies that the default input or output unit is to be accessed.
The keyword UNIT is optional only if the logical unit specifier is the first
parameter in the control list.
A logical unit number is assigned to a file or device in one of two ways:
•
•

7. 1. 1 .3

Explicitly through an OPEN statement (see Section 9.1)
Implicitly by the system (see the VAX FORTRAN User Manual for more
information on implicit logical assignments).

Internal File Specifier

The internal file specifier identifies the internal file to be used. It takes the
following form:
[UNIT=) cv

Is a character scalar memory reference or a character array name reference.
The external logical unit specifier and the internal file specifier are mutually exclusive. The keyword UNIT is optional if the internal file specifier
is the first parameter in the control list.
See the VAX FORTRAN User Manual for more information on internal
files.
7. 1. 1.4

Format Specifiers

The format specifier stipulates either explicit or list-directed formatting . In
the case of explicit formatting, it also identifies the parameter that controls
formatting. The format specifier takes either one of the following forms:
[FMT=] f
[FMT=] *

7-4 1/0 Statements

f
Is the statement label of a FORMAT statement; an integer variable that
has been assigned a FORMAT statement label with an ASSIGN statement;
the name of an array or array element containing a run-time format; or a
character expression containing a run-time format.

Specifies list-directed formatting.
The keyword FMT is optional only if the format specifier is the second
parameter in the control list, and the first parameter is a logical unit or
internal file specifier without the optional keyword UNIT.
Chapter 8 describes FORMAT statements. Section 8.8 describes the
interaction between formats and I/O statements.
In sequential I/O statements, you can use an asterisk instead of a format specifier to denote list-directed formatting (see Sections 7.2.1.2 and
7.3.1.2).
7. 1.1.5

Namelist Specifier

The namelist specifier stipulates namelist-directed IjO. It identifies the
group-name of the list of entities that may be modified on input or written
on output.
The namelist specifier takes the following form:
[NML;]group-name

group-name
Is the name of a list previously defined in a NAMELIST statement.

The keyword NML is optional only if the following conditions are true:

•

The firs t parameter is a logical unit specifier without an optional UNIT
keyword.

•

The namelist specifier is the second parameter in the control list.

A nam elist specifier cannot be used in a statement that contains a format
specifier.

1/0 Statements 7-5

7. 1. 1.6

Record Specifier

The record specifier identifies the number of the record you wish to access
in a file with relative organization. It takes either one of the following
forms:
REC = r
'r

r
Is a numeric expression with a value that represents the position in a
direct access file of the record to be accessed. The value must be greater
than or equal to one, and less than or equal to the maximum number of
records allowed in the file. If necessary, a record n umber is converted to
integer data type before being used .
7.1. 1.7

Key-Field- Value Specifier

The key-field-value specifier identifies the key field of a record that you
wish to access in an indexed file. The key-field value is equal to the
contents of a key field. The key field contains such information as the
number, direction, length, byte offset, and type of the fields. It can be
used to access records in indexed files because it determines their location.
The attributes of the key field are specified at file creation. Records in an
indexed file have the same attributes for their key fields.
Key-field -value specifiers have two components:
•

An expression (val) that specifies a value used to compare with
key-field values.

•

A selection condition keyword (such as KEY) that specifies how to
compare val with key-field values.

The y take the following forms:

Ascending Keys
KEY = val
KEYEQ = val
KEY NXT = val
KEYNXTN E = val
KEYGT = val
KEYGE = val

7-6 1/0 Statements

Descending Keys
KEY = val
KEYEQ = va l
KEYNXT = val
KEY NXTNE = val
KEYLT = va l
KEYLE = val

val
Is an integer or character expression. Integer expressions must compare
with integer key fields; they cannot contain real or complex values.
Character expressions must compare with character key fields; they must
be ASCII strings made up of either characters or BYTE (LOGICAL*l) array
names containing Hollerith data .

The Selection Condition

The selection condition determines how val is compared with key-field
values. The keyword can be any one of the following specifiers:

Ascending Keys
•
•

KEY and KEYEQ-the value in the key fi eld must be equal to val.
KEYNXT-the value in the key field must be the next value of the key
equal to or greater than val.

•

KEYNXTNE-the value in the key field must be the next value of the
key strictly greater than val.

•

KEYGT-the value in the key field must be greater than val.

•

KE YGE-the value in the key field must be greater than or equal to
val.

Descending Keys
•

KEY and KEYEQ-the value in the key field must be equal to val.

•

KEYNXT-the value in the key field must be the next valu e of the key
equal to or less than val.

•

KEYNXTNE-the value in the key field must be th e next value of the
key that is strictly less than val.

•

KEYL T-the value in the key field must be less than val.

•

KEYLE-the value in the key field must be less than or equal to val.

1/0 Statements 7-7

Keyword specifiers are interchangeable between ascending-key files and
descending-key file s-except KEYGT, KEYGE, KEYL T, and KEYLE. These
fo ur keywords are one-directional. If you use them with keys going in the
opposite direction, the Run-Time Library (RTL) displays an error at run
time.
KEYNXT and KEYNXTNE are interchangeable between ascending-key files
and descending-key files . Unlike KEY and KEYEQ, they are interpreted
differently depending on the direction of the keys in the file. In ascendingkey files, KEYNXT is the same as KEYGE, and KEYNXTNE is the same
as KEYGT. In descending-key files, KEYNXT is the same as KEYLE, and
KEYNXTNE is the same as KEYL T.
You should use KEYGT and KEYGE when exclusively accessing ascending keys and, similarly, KEYLT and KEYLE when exclusively accessing
descending keys . When a program must be able to use either kind, you
should use KEYNXT and KEYNXTNE.

The Selection Process
To select key- field integer values, the process compares values using the
signed integers themselves.
To select key-field character values, the process compares values using the
ASCII collating sequence. Additionally, the comparative length of val and
a key-field value, and the specified selection condition determine the kind
of selection th at occurs: exact, generic, or approximate-generic.
Exact selections occur when the expression in val is equal in length to
the expression in the key field of the currently accessed record and the
keyword specifies a unique selection.
Generic selections occur when the expression in val is shorter than the
expression in the key field of the currently accessed record and the
keyword specifies a unique selection. The process compares all the
characters in val, from left to right, with the same amount of characters
in the key field , also from left to right. Remaining key-field characters are
ignored.
For example, if val is 'ABCD' and a record's key-field is 10 characters long,
and you specifi ed an equal selection, the process could select a record with
a key-field value 'ABCDEFGHIJ'.
An approximate-generic selection occurs when val is shorter than the
expression in the key field and the keyword (KEYGT, KEYGE, KEYLT,
KEYLE, KEYN XT, and KEYNXTNE) does not specify a unique selection.
As with generic selections, the process uses only the leftmost characters in

7-8 1/0 Statements

the key-field to compare values. It selects the first key fi eld that satisfies
the generic selection criterion .
For example, if val is 'ABCD' and a record 's key-field val ue is 5 characters
long and you specify a greater-than selection, the process could select the
key-field value 'ABCEx' (and not the key-field value 'ABCDA').
No selection occurs if val is longer than the key-field value. The RTL
displays an error message.
7 .1.1.8

Key - of- Reference Specifier

The key-of-reference specifier may optionally accompany the key-fieldvalue specifier; it designates the key-field index that is search ed to find
the specified key-field value. Key-of-reference specifiers take the following
form:
KEY ID= kn

kn
Is an integer expression, called the key-of-reference n umber, that designates the key field index to be searched.
The key-of-reference number is an integer value in the range zero to the
maximum key number defined for the file. A value of zero specifies tbe
primary key, a value of one specifies the first alternate key, and so forth .
If no key-of-reference number is given, it defaults to th e last spedfication
given in a keyed 1/0 statement for that logical unit.

7 .1.1.9

1/0 Status Specifier
The I/O status specifier designates a variable in which is a stored value
that indicates whether an error or end-of-file condition exists:
•

If the value is zero, no error or end-of-file condition exists.

•

If the value is positive, an error condition exists.

•

If the value is negative, an end-of-file condition exists but an error
condition does not.

The I/O status specifier takes the following form:
IOSTAT=ios

1/0 Statements 7-9

ios

Is an integer scalar memory reference.
See the VAX FORTRAN Us er Manual for more information on the error
numbers returned by IOSTAT.
7. 1. 1. 10

Transfer-of-Control Specifiers

The transfer-of-control specifier identifies an executable statement and
transfers control to that statement if an end-of-file or error condition
occurs. It takes either one of the following forms:
END=s
ERR=s

s
Is the label of the executable statement that receives control.
A sequential READ statement can include either or both of the previous
specifications, in any order. WRITE,REWRITE, direct access READ,and
keyed access READ statements can include only the ERR=s specification.
The statement label in the END=s or ERR=s specification must refer to
an executable statement within the same program unit as that of the 1/0
statement.
An end-of-file condition occurs when no more records exist in a file during
a sequential read, or when an end-of-file record produced by the ENDFILE
statement is encountered (see Section 9.6). End-of-file conditions do not
occur in direct accessor keyed access READ statements.
If a READ statement encounters an end-of-file condition during an I/O
operation, it transfers control to the statement designated by the END=s
specification. If there is no END=s specification, control transfers to
the statement designated by the ERR=s specification. If there is neither
specification (nor an IOSTAT specifier), the program terminates.
If a READ, WRITE,or REWRITE statement encounters an error condition
during an I/O operation, it transfers control to the statement whose label
appears in the ERR=s specification. If neither an ERR specifier nor an
IOSTAT specifier is present, the I/O error terminates program execution.

See the VAX FORTRAN User Manual for a description of system subroutines that you can use to control error processing. To obtain information
from the 1/0 system on the type of error that occurred, use the IOSTAT
parameter discussed in Section 7.1.1. 9.

7-1 0 I/ 0 Statements

Examples

The following READ statement transfers control to statement 550 if an
end-of-file condition occurs on logical unit 8.
READ (8 ,END=550) (MATRIX(K) ,K=1 , 100)

The following WRITE statement transfers control to statement 390 if an
error occurs while it is being executed.
WRITE (6,50,ERR=390) VAR1 , VAR2, VAR3

The following READ statement transfers control to statement 150 (if
an error occurs while it is being executed) or to statement 200 (if an
end-of-file condition occurs).
READ (1 ,FORM,ERR=150,END=200) ARRAY

7.1.2

1/0 List
The I/O list in an input or output statement contains the scalar references,
array name references, and aggregate referencesspecifying the memory locations from which or to which data will be transferred. (See Section 2.2.6
for a description of the different types of references .)
The I/O list in an input statement cannot contain constants and expressions because these do not specify named memory locations that can be
referenced later in the program. The I/O list in an output statement can
contain constants and expressions, however, because the compiler can use
temporary memory locations to hold these values during the execution of
the I/O statement.
An I/O list takes the following form:
s [, s] . . .

s
Is a simple list element or an implied-DO list.
The I/O statement assigns values to (or transfers values from) the list
elements in the order in which they appear, from left to right.

1/0 Statements

7-11

7 .1.2. 1

Simple List Elements

A simple 1/0 list element can be a scalar reference, scalar array name
reference, or aggregate reference; for example:
WRITE (5 , 10) J, K(3). 4, (L+4)/2 , N

When you use an array name reference or an aggregate reference in an
1/0 list, an input statement reads enough data to fill every element of the
array or aggregate . An output statement writes all of the values in the
array or aggregate .
Data transfer begins with the initial element of the array and proceeds in
the order of subscript progression, with the leftmost subscript varying most
rapidly; for example, the following statement defines a two-dimensional
array:
DIMENSION ARRAY(3,3)

If the name ARRAY, with no subscripts, appears in a READ statement,
that statement assigns values from the input record(s) to ARRAY(l,1),
ARRAY(2,1), ARRAY(3,l), ARRAY(l,2), and so on through ARRAY(3,3).

In an input statement, variables in the 1/0 list can be used in array
subscripts later in the list; for example:
READ (1 , 1250) J, K. ARRAY(J,K)
1250 FORMAT (I1,1X , I1,1X,F6 .2)

The input record contains the following values:
1 ,3,721 . 73

When the READ statement is executed, the first input value is assigned to
J and the second to K, thereby establishing the actual subscript values for
ARRAY(J,K). Then the value 721.73 is assigned to ARRAY(l,3). Variables
that are to be used as subscripts in this way must appear before (to the left
of) their use as the array subscripts in the 1/0 list.
An output statement 1/0 list may contain any valid expression. However,
this expression must not attempt any further 1/0 operations on the same
logical unit. For example, an output statement 1/0 list expression must
not refer to a function subprogram that performs 1/0 on the same logical
unit.
An input statement 1/0 list must not contain a constant or an expression,
except as a subscript expression in an array reference or as an expression
in a substring reference.

7-12

1/0 Statements

Aggregate references can be used only in unformatted input and output
statements. When multiple array names or aggregate references are used
in the I/O list of an unformatted input or output statement, only one
record is read or written regardless of how many array name references or
aggregate referencesappear in the list.
7 .1.2.2

Implied-DO Lists in 1/0 Statements

An implied-DO list is an I/O list element that acts as though it were a
part of an I/O statement within a DO loop. Implied-DO lists can achieve
the following:
•
•
•

Specify iteration of part of an I/O list
Transfer part of an array
Transfer array elements in a sequence different from the order of
subscript progression

An implied-DO list takes the following form:
(list, i=e1,e2[ , e3])

list
Is an I/O list.
I

Is an integer or real variable.
e1,e2,e3
Are arithmetic expressions.
The variable i and the parameters el, e2, and e3 have the same forms and
the same functions that they have in the DO statement (see Section 5.3).
The list immediately preceding the DO loop parameter is the range of the
implied-DO loop. Elements in that list can reference i, but they must not
alter the value of i.
Examples

The following examples demonstrate valid implied-DO lists.
•

The following two WRITE statements have the same effect:
WRITE (3 , 200) (A ,B,C, !=1,3)
WRITE (3,200) A,B,C,A,B,C,A,B,C

1/0 Statements 7-13

•

In the next example, the I/O list consists of an implied-DO list
containing another implied-DO list nested within it:
WRITE (6) (I,

•

Together, the implied-DO lists write a total of (1+3•L)•M fields,
varying the Js for each value of I.
In a series of nested implied-DO lists, parentheses indicate the nesting
(see Section 5.3.1.2). Execution of the innermost lists is repeated most
often:
150

•

WRITE (6,150) ((FORM(K,L), L=1,10), K=1,10,2)
FORMAT (F10.2)

Because the inner DO loop is executed 10 times for each iteration of
the outer loop, the second subscript, L, advances from 1 through 10
for each increment of the first subscript. This is the reverse of the
order of subscript progression. In addition, K is incremented by 2;
thus, only the odd-numbered rows of the array are output.
The entire list of an implied-DO list is transmitted before the control
variable is incremented:
READ (5,999)

•

(J,P(I),Q(I,J), J=1,L), I=1,M)

(P(I),

(Q(I,J), J=1,10), I=1,5)

In this example, P(l), Q(l,l), Q(l,2) ... ,Q(l,10) are read before I is
incremented to 2.
When processing multidimensional arrays, you can use a combination
of fixed subscripts and subscripts that vary according to an implied-DO
list:
READ (3,5555) (BOX(1,J). J=1,10)

•

This statement assigns input values to BOX(l,1) through BOX(l,10)
and then terminates without affecting other elements of the array.
The value of the control variable can also be output directly:
WRITE (6, 1111) (I, I=1, 20)

This statement prints the integers 1 through 20.
If the I/O statement containing an implied-DO list terminates abnormally
(with an END= or ERR= transfer or with an IOSTAT value other than
zero), the loop control variable becomes undefined.

7-14 1/0 Statements

7.2 READ Statements
The READ statement transfers input data to internal storage from records
contained in external logical units or to internal storage from internal files.
VAX FORTRAN provides the following kinds of READ statements:
•
•
•
•

7.2.1

Sequential
Direct
Internal
Indexed

Sequential READ Statements
Sequential READ statements transfer input data to internal storage from
external records that were sequentially accessed. They can be formatted,
list-directed, namelist-directed, or unformatted, taking one of the following
forms:

Formatted
READ (extu,fmt[,iostat] [,err] [,end]) [iolist]
READ f [ . i olist]

List-Directed
READ (extu. * [ .iostat] [ , err] [,end]) [iolist]
READ * [, io l ist]

Name list-Directed
READ ( e xtu . nml [. iostat] [ . err] [ .end] )
READ n

Unformatted
READ (extu[.iostat] [ , err] [.end]) [iolist]

Control-list parameters are symbolized as follows:

extu-a logical unit specifier
fmt-a format specifier

1/0 Statements 7-15

f-the nonkeyword form of a format specifier
•-a list-directed format specifier (You can also use FMT=•.)

nml-a namelist specifier
n-the nonkeyword form of a namelist specifier

iostat-an I/O status specifier

err, end-transfer-of-control specifiers
The 1/0-list parameter is symbolized as follows:

iolist-the I/O list specifier
The parameters in 1/0 statements are fully described in Sections 7.1.1
(control-list parameters) and 7.1.2 (1/0-list parameter). Their syntax rules
are summarized in Section 7.1.1.1.
7 .2.1.1

Formatted Sequential READ Statement

The formatted sequential READ statement performs the following operations:
•
•
•

Reads character data from one or more external records accessed under
the sequential or keyed mode of access.
Translates the data from character to binary form using format specifications to provide editing.
Assigns the translated data to the elements in the 1/0 list, in the
order, from left to right, in which those elements appear in the list.

If the number of 1/0 list elements in a statement is less than the number
of fields in an input record, the statement ignores the excess fields .

See Section 7.2.3 for information about the combined use of formatted
sequential READ statements and indexed READ statements under the
keyed mode of access

7-16 II 0 Statements

7 .2.1.2

List-Directed Sequential READ Statement
The list-directed sequential READ statement performs the following
operations:
•
•

•

Reads character data from records accessed under the sequential mode
of access.
Translates data from external to binary form using the data types of
the elements in the 1/0 list, and the forms of the data, to provide
editing.
Assigns the translated data to the elements in the 1/0 list in the order,
from left to right, in which those elements appear in the list.

The external records from which list-directed READ statements read data
contain a sequence of values and value separators. A value in one of these
records may be any one of the following:
•

A constant: Each constant has the form of the corresponding

FORTRAN constant. Input constants can be any of the following
data types: integer, real, logical, complex, and character. The data
type of the constant determines the data type of the value and the
translation from external to internal form.
A numeric list element can correspond only to a numeric constant, and
a character list element can correspond only to a character constant. If
the data types of a numeric list element and its corresponding numeric
constant do not match, conversion is performed according to the rules
for arithmetic assignment (see Table 3-1).
A complex constant has the form of a pair of real or integer constants
separated by a comma and enclosed in parentheses. Spaces can occur
between the opening parenthesis and the first constant, before and
after the separating comma, and between the second constant and the
closing parenthesis.
A logical constant represents true or false values: .TRUE. or any value
beginning with T, .T, t, or .t; or .FALSE. or any value beginning with
F, .F, f, or .f.
A character constant must be delimited by apostrophes. An apostrophe occurring within a character constant is represented by two
consecutive apostrophes.
Hollerith, octal, and hexadecimal cons tants are not permitted.

1/0 Statements 7-17

•

A null value: A null value is specified by two consecutive commas
with no intervening constant or by an initial comma or trailing comma.
Spaces can occur before or after the commas. A null value indicates
that the corresponding list element remains unchanged. A null value
can represent an entire complex constant, but cannot be used for either
part of a complex constant.

•

A repetition of constants in the form r•c: The form r•c indicates r
occurrences of c, where r is a nonzero, unsigned integer constant and
c is a constant. Spaces are not permitted except within the constant c
as previously specified.

•

A repetition of null values in the form r•: The form r* indicates r
occurrences of a null value, where r is an unsigned integer constant.

A record can use any one of the following entities as a value separator,
with or without surrounding spaces of tabs:
•
•

Space or tab
Comma

•

Slash

The slash terminates processing of the input statement and the record,
leaving all remaining 1/0 list elements unchanged.
When any of the preceding entities appear in a character constant, they
are considered part of the constant, not value separators.
The end of a record is equivalent to a space character except when it
occurs in a character constant. In this case, the end of the record is
ignored, and the character constant is continued with the next record (the
last character in the previous record is immediately followed by the first
character of the next record).
Spaces at the beginning of a record are ignored unless they are part of a
character constant continued from the previous record. In this case, the
spaces at the beginning of the record are considered part of the constant.
Each input statement reads one or more records as required to satisfy the
1/0 list. If a slash separator occurs or the 1/0 list is exhausted before all
of the values in a record are used, the remainder of the record is ignored.

7-18

1/ 0 Statements

Example

Consider a program unit with the following statements:
CHARACTER*14 C
DOUBLE PRECISION T
COMPLEX D, E
LOGICAL L,M
READ (1 ,* ) I , R,D, E,L,M, J , K, S,T,C,A, B

And the external record that will be read:
4 6 . 3 (3.4,4.2) , (3 , 2) . T.F . ,3*14 .6 . 'ABC . DEF/GHI' ' JK'/

Upon execution of the program unit, the following values are assigned to
the 1/0 list elements:
1/0 List Element

Value

6.3

(3.4,4 .2)

(3.0,2.0)

.TRUE.

.FALSE .

14.6

14.6DO

ABC, DEF /GHI'JK

A, B, and J are unchanged.

1/0 Statements

7-19

7 .2.1.3

Namelist-Directed Sequential READ Statement

The namelist-directed sequential READ statement performs the following
operations:
•
•

•

Reads data from external records accessed under the sequential mode
of access until it finds the specified group-name.
Translates the data from external to internal form using the data types
of the entities in the corresponding NAMELIST statement, and the
forms of the data, to provide editing.
Assigns the translated data to the specified namelist entities in the
order in which the entities appear in the input records .

The input for a namelist-directed READ consists of a record or records
delimited by the special symbol dollar sign ($), which starts in the second
column of the first record.
Namelist input takes the following form:
column 2

$group-name entity= value [,entity= value , ... ] $[END]

$
Is the special symbol used to indicate the beginning or end of input. The
ampersand (&) can be used in place of the dollar sign.
group-name
Is the name of the namelist that contains the entity or entities to be given
values. The namelist must have been previously defined in a NAMELIST
statement in the program unit.
entity
Is a namelist-defined entity. The entity can be a variable, array name,
subscripted variable, variable with a substring, or subscripted variable
with a substring.
value
Is a constant, a list of constants, a repetition of constants in the form r*c,
or a repetition of values in the form r* (see Section 7.2.1.2).

END
Is an optional part of the last delimiter.

7-20

1/0 Statements

Information on syntax rules for namelist input, prompting for curren t
values, and assigning values is presented separately under the headings
that follow.
Syntax Rules

The following syntax rlAles apply to namelist input:

•

The group-name cannot contain spaces or tabs and must be contained
within a single record.

•

The entities appearing on the left side of the equal sign in a value assignment cannot contain spaces or tabs except within the parentheses
of a subscript or substring specifier. Each entity must be contained in
a single record.

•

Each constant that appears in a value assignment has the fo rm of
the corresponding FORTRAN constant. A complex constant has the
form of a pair of real or integer constants separated by a comma
and enclosed in parentheses. Spaces can occur between the opening
parenthesis and the first constant, before and after the separating
comma, and between the second constant and the closing parenthesis.

•

A logical constant represents true or false values: .TRUE. or any value
beginning with T, .T, t, or .t; or .FALSE. or any value beginning with
F, .F, f, or .f. A character constant is delimited by apostrophes. An
apostrophe occurring within a character constant is represented by two
consecutive apostrophes . Hollerith, octal, and hexadecimal constants
are not permitted.

•

The valid separators in a list of constants are spaces, tabs, and commas. Except within a character constant, any number of consecutive
spaces and tabs is equivalent to a single space. A null value is specified by two consecutive commas, by an initial comma, or by a trailing
comma. A separating comma preceded or followed by spaces is equivalent to a single comma. A null value indicates that the corresponding
namelist array element is unchanged. A null value can represent an
entire complex constant, but it cannot be used for either part of a
complex constant.
The form r•c indicates r occurrences of c, where r is a nonzero, unsigned integer constant and c is a constant. Spaces are not permitted
except within the constant c in complex or character constants.

•
•

The form r* indicates r occurrences of a null value, where r is an
unsigned integer constant.

1/0 Statements 7-21

•

The valid separators in a list of value assignments are spaces, tabs, and
commas. Any number of consecutive spaces and tabs is equivalent to
a single space. A separating comma preceded or followed by spaces is
equivalent to a single comma. Consecutive commas are not permitted.

•

The equal sign in a value assignment can be preceded and followed
by any number of spaces or tabs.
The end of a record in namelist input is equivalent to a space character
except when the end of the record occurs in a character constant. If
this occurs, the end of the record is ignored, and the character constant
is continued with the next record; that is, the last character in the
previous record is followed immediately by the second character of
the next record. The first character is used for carriage control.

•

Prompting for Current Values
If your program is executing a namelist READ statement, you may prompt
it for the group name and name list entities that it will accept. To do this,
enter a question mark (?) record character. If you precede the question
mark with an equal sign ( =? ), the group name and current values of the
namelist entities for that group are displayed as in namelist output (see
Section 7.3.1.3).
Assigning Values

Input values can be assigned in any order using an assignment of the
form: entity=value. Each new line of input can begin in column 2 or in
any column thereafter. Column 1 of each record is assumed to contain a
FORTRAN carriage-control character. Any data placed in that column is
ignored.
Assigned values, array subscripts, and substring specifiers must be constant values. Symbolic (PARAMETER) constants are not permitted.
Input values can be any of the following data types: integer, real, logical,
complex, and character. If the data type of a namelist entity and its assigned constant value do not match, conversion is performed according to
the rules for arithmetic assignment (see Table 3- 1). Conversion between
numeric and character data types is not permitted.

7-22 1/0 Statements

Examples

In the first example, th e NAMELIST statement associates th e group-name
CONTROL with a list of five entities . The corresponding REA D statement
reads input data and assigns values to specified namelist entities.
NAMEL IST / CO NT ROL / TITLE , RESET, START, STOP , I NTERVAL
CHARACTER*10 TITLE
REAL*8 START, STOP
LOGICAL *4 RESET
I NTEGER*4 I NTERVAL
READ (U NIT=1, NML=CO NTROL)

In the next example, values are assigned to all of the namelist entities
previously associated with the group-name CONTROL.
column 2

$CO NTROL
~ TITLE='TESTT002AA' ,
IT AB j I NTERVAL=1 ,
ITABj RESET= TRUE.
~ START=1 0.2 ,
~ STOP =14 5
$END

Upon program execution, values are assigned to list entities as follo ws:
Entity

Value

TITLE

TESTT002A A

RES ET

START

10.2

STOP

14.5

INTERVAL

It is n ot necessary to assign values to all of the lis t en ti ties defined in the
corresponding NAMELIST group-name.
The na m elist-directed REA D statement does not change the values of
namelist entities that do not appear in the input data. Similarl y, when
character substrings and array elements are specified, only the values of
the specified variable substrings and array elements are changed . For
example, if the next input to the character variable TITLE used in the last
example contains the following statement:

1/0 Statements

7-23

column 2

•

$CONTROL TITLE(9 : 10)='BB' $END

Its new value is TESTT002BB; the first eight positions of the variable do
not change.
When a list of values is assigned to an array name, the first value in
that list is assigned to the first element of the array, the second value is
assigned to the second element of the array, and so on. The number of
array elements assigned must be less than or equal to the size of the array.
Consecutive commas within a list indicate that the values of the array
elements remain unchanged. Consider the following example:
A program unit contains the following statements:
DIMENSION ARRAY(20)
NAMELIST /ELEM/ ARRAY
READ (UNIT=1 , NML=ELEM)

The input contains the following:
column 2

•

$ELEM
ARRAY=1 . 1, 1 . 2, , 1 .4$END

Upon program execution, the READ statement assigns values to array
elements as follows:
Array Element

Value

ARRAY(l)

1.1

ARRAY(2)

1.2

ARRAY(3)

unchanged

ARRAY(4)

1.4

ARRAY(5)- ARRAY(20)

unchanged

When a list of values is assigned to an array element, the assignment
begins with the specified array element, rather than with the first element
of the array. In this example, if the next input to ARRAY consists of the
following:
column 2

•

$ELEM
ARRAY (3)=34 . 54 , 45 . 34, 87.63, 3*20 .00
$END

7-24 1/0 Statements

Upon program execution, the READ statement assigns new values only to
ARRAY elements 3 through 8. It does not alter unspecified elements.
7.2.1.4

Unformatted Sequential READ Statement

The unformatted sequential READ statement reads an external record
accessed under the sequential or keyed mode of access; it assigns the
fields of binary data contained in that record to the elements in the I/O
list, in the order, from left to right, in which those elements appear in the
list. The data is not translated and the amount of data assigned to each
element is determined by the element's data type.
The unformatted sequential READ statement reads exactly one record. If
the I/O list does not use all of the values in a record, the remainder of the
record is discarded; this happens when there are more values in the record
than elements in the list. If the number of list elements is greater than the
number of values in the record, an error occurs.
If a statement contains no I/O list, it skips over one full record, positioning
the file to read the following record on the next execution of a READ
statement.
Examples

In the first example, the READ statement reads one record from the file
connected to logical unit 1 and assigns values of binary data to variables
FIELDl and FIELD2, in that order.
READ (UNIT=1) FIELD1 , FIELD2

In the second example, the READ statement advances the file connected
to logical unit 8 by one record.
READ (8)

1/0 Statements 7-25

7.2.2

Direct Access READ Statements
Direct access READ statements transfer input data to internal storage from
external records accessed under the direct mode of access. They can be
formatted or unformatted, taking one of the following forms:

Formatted
READ (extu, rec, fmt [, iostat] [,err]) [iolist]

Unformatted
READ (extu,rec[.iostat] [,err]) [iolist)

Control-list parameters are symbolized as follows:

extu-a logical unit specifier
rec-a record specifier
fmt-a format specifier
iostat-an 1/0 status specifier
err-a transfer-of-control specifier
The 1/0-list parameter is symbolized as follows:

iolist-the 1/0-list specifier
The parameters in 1/0 statements are fully described in Sections 7.1.1
(control-list parameters) and 7.1.2 (1/0-list parameter) and their controllist syntax rules are summarized in Section 7.1.1.1.
7 .2.2. 1

Formatted Direct Access READ Statement

The formatted direct access READ statement performs the following
operations:

7-26

•

Reads character data from one or more external records accessed under
the direct mode of access.

•

Translates the data from character to binary form using format specifications to provide editing.

•

Assigns the translated data to the elements in the 1/0 list in the
left-to-right order in which the elements appear.

1/0 Statements

If the I/O list and formatting do not use all of the characters in a record,
the remainder of the record is discarded. If the I/O list and formatting
require more characters than are contained in the record, the remaining
fields are read as spaces.

Example

In the following example, the READ and FORMAT statements read
the first 10 fields from record 35 in the file connected to logical unit 2,
translate the values to binary form, and then assign the translated values
to the internal storage locations of the 10 elements of the array NUM.
10

7 .2.2.2

READ (2,REC=35,FMT=10) (NUM(K). K=1.10)
FORMAT (1012)

Unformatted Direct Access READ Statement
The unformatted direct access READ statement reads an external record
accessed under the direct mode of access; it assigns the fields of binary
data contained in that record to the elements in the I/O list, in the order,
from left to right, in which those elements appear in the list. The data is
not translated. The amount of data assigned to each element is determined
by that element's data type.
The unformatted direct access READ statement reads exactly one record.
If that record contains more fields than there are elements in the I/O
list of the statement, the unused fields are discarded; if there are more
elements than fields, an error occurs.
Examples

In the first example, the READ statement reads record 10 in the file
connected to logical unit 1 and assigns binary integer values to elements 1
and 8 of the array LIST.
READ (1'10) LIST(1), LIST(8)

In the second example, the READ statement reads record 58 in the file
connected to logical unit 4 and assigns binary values to five elements of
the array RHO .
READ (4.REC=58,IOSTAT=K,ERR=500) (RHO(N). N=1,5)

1/0 Statements

7-27

7.2.3

Indexed READ Statements
Indexed READ statements transfer input data to internal storage from
external records using keyed access.
In an indexed file, a series of records can be read in key value sequence
by using an indexed READ statement together with a sequential READ
statement. The first record in the sequence is read using the indexed
statement and the rest are read using sequential READ statements.
Indexed READ statemen ts can be formatted or unformatted, taking one of
the following forms:

Formatted
READ ( extu, fmt , k ey [ ,key i d] [ , i ostat] [ , err]) [ io list]

Unformatted
READ (extu , key[ , keyid] [.iostat] [ , err]) [iolist ]

Control-list parameters are symbolized as follows:

extu-a logical unit specifier
fmt-a form at specifier
key-a key specifier
keyid-a key-of-reference specifier
iostat-an I/O status specifier
err-transfer-of-control specifier
The I/0-list parameter is symbolized as follows :

iolist-the I/0-list specifier
All of the parameters used in I/O statements are described in Sections
7.1.1 (control-list parameters) and 7.1.2 (I/0-list parameter). The rules for
specifying control-list parameters are summarized in Section 7.1.1.1.

7-28 1/0 Statements

7 .2.3.1

Formatted Indexed READ Statement

The form atted indexed READ statement performs the following operations:
•
•
•

Reads character data fro m one or more external records accessed under
the keyed mode of access .
Translates the data from character to binary for m using forma t specifications to provide editing.
Assigns the translated values to the elements in the I/O list, in the
order, from left to right, in which they appear in the list.

The formatted indexed READ statement can be used onl y on indexed files.
If the I/O list and format specifications specify that ad ditional records are
to be read, the statement reads those additional records sequentially using
the current key-of-reference value.
If the KEYID parameter is omitted, the key-of-reference remains unchanged from the most recent specification. If the KEY ID parameter is
omitted from the first keyed read, the key-of-reference is the primary key.
If the specified key value is shorter than the key field referred to, the key
value is matched against the leftmost characters of the appropriate key
field until a match is found . The record supplying the m atch is then read.
If the key value is longer than the key fi eld referred to, an error occurs.
Example

In the following example, the READ sta tement retrieves a record with
a key value of 'ABCD ' in the primary key, and then uses the format
contained in the array item KAT( 25 ) to read th e firs t four fields from the
record into variables A,B,C, and D.
READ (3 ,KAT(25) ,KEY=' ABCD' ) A,B,C,D

1/0 Statements

7-29

7 .2.3.2

Unformatted Indexed READ Statement

The unformatted indexed READ statement reads an external record
accessed under the keyed mode of access. It assigns the fields of binary
data contained in that record to the elements in the 1/0 list, in the order,
from left to right, in which those elements appear in the list. The data is
not translated. The amount of data assigned to each element is determined
by the element's data type.
The unformatted indexed READ statement reads exactly one record, and
may be used only on indexed files. If the number of I/O list elements is
less than the number of fields in the record being read, the unused fields
in the record are discarded . If the number of 1/0 list elements is greater
than the number of fields , an error occurs.
If a specified key value is shorter than the key field referred to, the key
value is matched against the leftmost characters of the appropriate key
field until a match is found. The record supplying the match is then read.
If the specified key value is longer than the key field that is referred to, an
error occurs.

Examples

In the first example, the READ statement reads from the file connected
to logical unit 3 and retrieves the record with the value 'SMITH' in the
primary key field (bytes 1 to 5) . The firs t two fi elds of the record retrieved
are placed in variables ALPHA and BETA, respectively.
OPEN (UN IT=3, STATUS= ' OLD' ,
1
ACCESS= 'KEYED' , ORGANIZATI ON='INDEXED ',
2
FORM='UNFORMATTED' ,
3
KEY=(1:5,30 :37, 18 :23))
READ (3,KEY='SMI TH') ALPHA, BETA

In the second example, the READ statement retrieves the first record
having a value equal to or greater than 'XYZDEF' in the second alternate
key field (bytes 18 to 23). The first field of that record is placed in the
variable IKEY.
READ (3,KEYGE='XYZDEF' ,KEYID=2,ERR=99) IKEY

7-30 1/0 Statements

7.2.4

Internal READ Statement
Internal READ statements transfer input data to internal storage from
an internal file . (This statement has an alternative statement, DECODE,
which is discussed in Appendix A.)
The internal READ statement can be formatted or list-directed, taking one
of the following forms:
Formatted
READ (intu. fmt [. iostat] [.err] [.end]) [iolist]

List-Directed
READ (intu, * [ ,io stat] [,err] [,end]) [ iolist]

Control-list parameters are symbolized as follows:

intu-an internal file specifier
fmt-a format specifier
•-a list-directed formatting specifier (You can also use FMT=•)

iostat-an I/O status specifier
err, end-transfer-of-control specifiers
The I/0-list parameter is symbolized as follows:

iolist-the I/0-list specifier
The parameters used in I/O statements are described in Sections 7.1.1
(control-list parameters) and 7.1.2 (I/0-list parameter). The rules for
specifying control-list parameters are summarized in Section 7.1.1.1.
7.2.4.1

Formatted Internal READ Statement

The formatted internal READ statement performs the following operations:
•
•

Reads character data from an internal file.
Translates the data from character to binary form using format specifications to provide editing.

•

Assigns the translated data to the elements in the I/O list in the
left-to-right order in which the elements appear.

1/0 Statements 7-31

Example

The following program segment reads a record and examines the first
character to determine whether the remaining data should be interpreted
as decimal, octal, or hexadecimal. It then uses internal-file reads to make
appropriate conversions from character string representations to binary.
INTEGER IVAL
CHARACTER TYPE. RECDRD *80
CHARACTER*(*) AFMT . IFMT. OFMT, ZFMT
PARAMETER (AFMT=' (Q ,A)
IFMT= (110)
OFMT=
1
ZFMT= '(Z8) ')
ACCEPT AFMT, ILEN, RECORD
TYPE= RECORD(1 : 1)
IF (TYPE . EQ . 'D') THEN
READ (RECORD(2 :MIN(ILEN, 11)). IFMT) IVAL
ELSE IF (TYPE . EQ . '0') THEN
READ (RECORD(2 :MI N(ILEN, 12)). OFMT) IVAL
ELSE IF (TYPE . EQ . 'X') THEN
READ (RECORD(2 :MI N(ILEN, 9)) .ZFMT) IVAL
ELSE
PRINT *. ERROR
END IF
END
I

7 .2.4.2

(011)' .

List-Directed Internal READ Statement
The list-directed internal READ statement performs the following operations:
•

Reads character data from an internal file .

•

Translates the data from external to binary form using the data types
of the elements in the I/O list and the forms of the data to provide
editing.

•

Assigns the translated data to the elements in the I/O list, in the
order, from left to right, in which those elements appear in the list.

N amelist-directed formatting is not permitted with an internal READ
statement. Refer to the VAX FORTRAN User Manual for information on
the characteristics and use of internal files.

7-32

1/0 Statements

7.3 WRITE Statements
The WRITE statement transfers output data from internal storage to userspecified external logical units (disks, printers, terminals, mailboxes) or to
internal files. It can be used in sequential, direct, keyed, or internal access
modes.
WRITE statements cannot write to existing records in an indexed file. For
statements that can perform this function in indexed files, refer to the
REWRITE statement discussed in Section 7.4.

7.3.1

Sequential WRITE Statements
Sequential WRITE statements transfer output data from internal storage to
external records accessed under the sequential mode of access. (See the
VAX FORTRAN User Manual for descriptions of the various access modes.)
Sequential WRITE statements can be formatted, list-directed, namelistdirected, or unformatted, taking one of the following forms:

Formatted
WRITE (ex tu . fmt [. iostat] [.err]) [iolist]

List-Directed
WRITE ( extu , * [ , iostat] [.err]) [iolist]

N amelist-Directed
WRITE (extu,nml[,iostat] [,err])

Unformatted
WRITE ( extu [ , iostat] [ , err]) [iolist]

Control-list parameters are symbolized as follows:

extu-a logical unit specifier

fm t-a format specifier
*-a list-directed formatting specifier (You can also use FMT=•)

nml-a namelist specifier

1/0 Statements

7-33

iostat-an I/O status specifier
err-a transfer-of-control specifier
The I/0-list parameter is symbolized as follows:

Formatted Sequential WRITE Statement

The formatted sequential WRITE statement performs the following operations:
•
•
•

Retrieves specified data from internal storage.
Translates the data from binary to character form using format specifications to provide editing.
Writes the translated values to an external record that is sequentially
accessed.

The length of the records written to a user-specified output device (for
example, a line printer) must not exceed the maximum record length that
the device can process. In the case of a line printer, this maximum is
usually 132 characters.
Using an appropriate format specification, a statement can write more than
one record.
If you transfer numeric data using formatted output statements and you
subsequently use the data as input, the resulting data may not be precise
because of a rounding of the data during conversion from binary to
character form. Therefore, if you expect to subsequently use numeric data
as input, use unformatted output and input statements for data transfer.

Examples

In the first example, the WRITE statement writes one record to logical
unit 6. The record consists of the character constant defined in the
FORMAT statement.
650

7-34 1/0 Statements

WRITE (6,650)
FORMAT (' HELLO THERE')

In the second example, the WRITE statement writes one record consisting
of fields AYE, BEE, and CEE to logical unit 1.
95

WRITE (1 ,95 ) AYE , BEE , CEE
FORMAT (3F8 5)

In the third example, the WRITE statement writes three separate records
to logical unit 1. Each record has only one field .
900

7 .3.1.2

WRITE (1,900) DEE , EEE, EFF
FORMAT (F8 . 5)

List-Directed Sequential WRITE Statement

The list-directed sequential WRITE statement performs the following
operations:
•

Retrieves specified data from internal storage.

•

Translates that data from binary to character form using the data type
of the elements in the I/O list to provide editing.

•

Writes the translated values to an external record accessed under the
sequential mode of access.

The values transferred as output by the list-directed WRITE statement
have the same forms as those of constant values transferred as input
by the list-directed READ and ACCEPT statements, with the following
exceptions:
•

Character constants are transferred without delimiting apostrophes.

•

Each internal apostrophe is represented by only one apostrophe
instead of two.

Consequently, records containing list-directed character output data can
be printed but not used for list-directed input. (See Section 7.2.1.2 for a
discussion of list-directed value forms.)
Table 7-1 shows the default output formats for each data type .

1/ 0 Statements

7-35

Table 7-1:

List-Directed Default Output Formats

Data Type

Output Format

LOGICAL*l(BYTE)

LOGICA L*2

LOGICAL*4

INTEGER*2

INTEGER•4

112

REAL

1PG15.7E2

REAL•8

1PG24.16E2

REAL•8(/ G _FLOATING)

1PG24.15E3

REAL*16

1PG43.3 3E4

COMPLEX

'(',1PG14.7E2, ',', 1PG14.7E2,')'

COMPLEX*l6

'(', 1PG23.16E2,',', 1PG23 .1 6E2,')'

COMPLEX•16( / G_FLOATING)

'(', 1PG23.15E3,' ,', 1PG23 .15E3,')'

CHARACTER

An .

where n is the length of the character
expression

List-directed output formats behave in the following ways:

•
•
•
•
•

7-36

1/0 Statements

List-directed output statements do not produce octal values, null
values, slash separators, or repeated forms of values.
List-directed output edits a complex value so that there are no embedded spaces in the value.
Each output record begins with a space for carriage control.
Each output statement writes one or more complete records .
Each individual output value is contained within a single record, with
the exception of character constants longer than one record length and
complex constants that can be split after the comma.

Example

The following example illustrates a valid list-directed WRITE statement:
DIMENSION A(4)
DATA A/4 *3 .4/
WRITE (1 ,* ) 'ARRAY VALUES FOLLOW'
WRITE (1 . *) A. 4

In this example, the WRITE statements write the following records to
logical unit 1:
ARRAY VALUES FOLLOW
3.400000
3.400000

7 .3 . 1.3

3 . 400000

3 .400000

Namelist-Directed Sequential WRITE Stat ement
The namelist-directed sequential WRITE statement performs the following
operations:
•

Retrieves data specified by the namelist specifier from internal storage.

•

Translates that data from internal to external form using the data type
of the list entities in the corresponding NAMELIST statement.
Writes the translated values to external records accessed under the
sequential mode of access.

•

The namelist-directed WRITE statement transfers as output the current
values of all list entities associated with the specified namelist specifier.
These values are written in a form that can be read as input by the
namelist-directed READ and ACCEPT statements.
The order of data output is dictated by the sequence in which n amelist
entities are defined in a NAMELIST statement . The firs t list entity and
its value are written first, the second list entity and its value are written
second, and so on. Each value display begins on a new line.

1/0 Statements

7-37

Example

Consider a program unit with the following statements:
CHARACTER*19 NAME(2)/2 * ' '/
REAL PITCH , ROLL, YAW , POSITIO N(3)
LOGICAL DIAG NOSTI CS
INTEGER ITERATIO NS
NAMELIST /PARAM/ NAME , PITCH , ROLL, YAW, POS I TIO N,
1
DIAGNOSTICS , ITERATIO NS

READ (UNIT=l,NML=PARAM)
WRITE (UNIT=l.NML=PARAM)

The input contains the following statements:
6$PARAM6 NAME(2)(10:)='HEISENBERG ',
6P ITCH=5.0, YAW=O.O, ROLL=5 . 0 ,
6DIAG NOSTICS= .TRUE .
6ITERAT IONS=10$END

In this case, the WRITE statement would write the following:
MPARAM
6NAME
6PITCH
5 .000000
6ROLL
5 . 000000
6YAW
O.OOOOOOOE+OO ,
6POSITIO N
= 3*0 .0000000E+OO ,
6DIAG NOSTICS
= T,
6ITERATIONS
10
MEND

HE ISENBERG' ,

Notice that character values are enclosed in apostrophes . The value
of POSITION is not defined in the namelist-directed input. It may be
defined elsewhere in the program or be undefined. The namelist-directed
WRITE statement prints the current contents of POSITION.

7-38

1/0 Statements

7 .3.1.4

Unformatted Sequential WRITE Statement

The unformatted sequential WRITE statement transfers specified binary data from internal storage to an external record accessed under the
sequential mode of access. The data is not translated.
The unformatted sequential WRITE statement writes exactly one record. If
there is no I/O list, the statement writes one null record.
Examples

In the first example, the WRITE statement writes a record to the file
connected to logical unit 1 containing the values (in binary form) of
elements 1 through 5 of the array LIST.
WRITE (1) (LIST(K), K=l , 5)

In the second example, the WRITE statement writes one null record to the
file connected to logical unit 4.
WRITE (4)

7.3.2

Direct Access WRITE Statements
Direct access WRITE statements transfer output data from internal storage to external records accessed under the direct mode of access. (The
attributes of a direct access file are established by the OPEN statement.)
Direct access WRITE statements can be formatted or unformatted, taking
one of the following forms:

Formatted
WRITE (extu, rec, fmt [, iostat] [,err]) [iolist]

Unformatted
WRITE (extu, rec[, iostat] [,err]) [iolist]

Control-list parameters are symbolized as follows:

extu-a logical unit specifier
rec-a record specifier
fmt-a format specifier
iostat-an I/O status specifier
err-transfer-of-control specifier
1/0 Statements

7-39

The I/0-list parameter is symbolized as follows:

iolist-the I/0-list specifier
The parameters used in 1/0 statements are described in Sections 7.1.1
(control-list parameters) and 7.1.2 (1/0-list parameter). The rules for
specifying control-list parameters are summarized in Section 7.1.1.1.

7 .3.2.1

Formatted Direct Access WRITE Statement
The formatted direct access WRITE statement performs the following
operations:
•

Retrieves binary values from internal storage.

•

Translates those values to character form using format specifications to
provide editing.

•

Writes the translated data to a user-specified external record accessed
under the direct mode of access.

If the values specified by the 1/0 list and formatting do not fill the output
record being written, the unused portion of the record is filled with space
characters. If the values overfill the record, an error occurs.

7 .3.2.2

Unformatted Direct Access WRITE Statement
The unformatted direct access WRITE statement retrieves binary values
from internal storage and writes those values to a user-specified external
record accessed under the direct mode of access. The values are not
translated.
If the values specified by the 1/0 list do not fill the output record being
written, the unused portion of the record is filled with zeros. If the values
do not fit in the record, an error occurs.

7-40 1/0 Statements

7.3.3

Indexed WRITE Statements
The indexed WRITE statement transfers output data from internal storage
to external records accessed under the keyed mode of access. (The OPE N
statement establishes the attributes of an indexed file.)
Indexed WRITE statements always write a new record . You should use
the REWRITE statement to update an existing record (see Section 7.4).
The syntactic for m of the indexed WRITE statement is identical to that
of the sequential WRITE sta tement. The two statements differ only in
that the indexed WRITE statement refers to a logical unit connected to an
indexed file, whereas the sequential WRITE statement refers to a logical
unit connected to a sequential file.
Indexed WRITE statements can be formatted or unformatted, taking one of
the following forms:

Formatted
WRITE (extu,fmt[,iostat] [ , err]) [iolist]

Unformatted
WRITE (extu[ , iostat] [ , err]) [iolist]

Control-list parameters are symbolized as follows:

extu- a logical unit specifier
fmt-a fo rmat specifier
ios tat-an I/O status specifier

err-a transfer-of-control specifier
The 1/ 0 -list parameter is symbolized as follows:

io list- the 1/ 0-list specifi er
The parameters used in I/ O statements are described in Sections 7.1.1
(control-list parameters) and 7.1.2 (I/0-list parameter). The rules for
speci fying control -list parameters are summarized in Section 7.1.1.1.

1/0 Statements

7-41

7 .3.3.1

Formatted Indexed WRITE Statement

The formatted indexed WRITE statement performs the following operations:
•

Retrieves binary values from internal storage.

•

Translates those values to character form using fo rma t specifications to
provide editing.

•

Writes the translated data to one or more external records accessed
under the keyed mode of access.

No key parameters are required in the list of control parameters because
all necessary key information is contained in the output record.
If the values specified by the I/O list and formatting do not fill a fixedlength record being written, the unused portion of the record is filled with
space characters. If additional records are specified, they are inserted in
the file logically according to the key values contained in each record.

When you write an INTEGER key using the formatted indexed WRITE
statement, the key is translated from internal binary for m to external
character form. A subsequent attempt to read the record using an integer
key may not match the key field in the record.
Example

In the following example, the formatted indexed WRITE statement writes
the translated values of each of the 20 elements of the array RDATA
to a new formatted record in the indexed file connected to logical unit
4. KEYVAL is the key by which the record is accessed. (This example
assumes that the first 10 bytes of a record are a character key.)
100

7-42

1/0 Statements

WRITE (4 , 100) KEYVAL,
FORMAT ( A10,20F15 7)

( RDATA (I), I=1,20)

7 .3.3.2

Unformatted Indexed WRITE Statement

The unformatted indexed WRITE statement retrieves binary values from
internal storage and writes those values to an external record accessed
under the keyed mode of access . The values are not translated .
No key parameters are required in the list of control parameters because
all necessary key information is contained in the output record.
If the values specified by the I/O list do not fill a fixed-length record being
written, the unused portion of the record is filled with zeros. If the values
specified overfill the record, an error occurs.

Using records (structured data items) has advantages when writing to
indexed files. Such files usually have a fixed record format. Thus, by
using a structure declaration that models the file 's record format, you can
accomplish the I/O operation with a single record variable instead of a
potentially long I/O list. For an example, refer to the VAX FORTRAN User
Manual.

7.3.4

Internal WRITE Statement
Internal WRITE statements transfer output data from internal storage to
an internal file. (You can also use the ENCODE statement discussed in
Appendix A to control internal output.) See the VAX FORTRAN User
Manual for information about the characteristics and use of internal files.
Namelist-directed formatting is not permitted with internal WRITE statements.
Internal write statements can be formatted or list-directed, taking one of
the following forms:
Formatted
WRITE (in tu, fmt [. iostat] [,err]) [iolist]

List-Directed
WRITE (intu , * [, i ostat ] [,e rr ]) [iolist]

Control-list parameters are symbolized as follows:
intu-an internal file specifier

fmt-a format specifier

1/0 Statements

7-43

*-a list-directed formatting specifier (You can also use FMT=*.)

iostat-an 1/0 status specifier

err-a transfer-of-control specifier
The I/0-list parameter is symbolized as follows :

iolist-the I/0-list specifier
The parameters used in 1/0 statements are described in Sections 7.1 .1
(control-list parameters) and 7.1.2 (I/0-list parameter). The rules for
specifying control-list parameters are summarized in Section 7.1.1.1.
7 .3.4.1

Formatted Internal WRITE Statement

The formatted internal WRITE statement performs the following operations:
•

Retrieves data from internal storage.

•

Translates that data from binary to character form using format
specifications to provide editing.
Writes the translated values to an internal file.

•
7 .3.4.2

List-Directed Internal WRITE Statement

The list-directed internal WRITE statement performs the following operations:
•

Retrieves data from internal storage.

•

Translates that data from binary to character form using the data type
of the elements in the I/O list to provide editing.
Writes the translated values to an internal file.

•

7-44 1/ 0 Statements

7.4 REWRITE Statement
The REWRITE statement transfers data from internal storage to the current
record in a file with indexed or relative organization. The current record
is the one that was most recently accessed by a successful direct access,
indexed, or sequential READ statement.
Between a READ and REWRITE statement, you should not issue any other
I/O statement (except INQUIRE) on that logical unit. Execution of any
other I/O statement on the logical unit destroys the current-record context
and causes the current record to become undefined.
REWRITE statements can be formatted or unformatted, taking one of the
following forms:

Formatted
REWRITE (extu , fmt [, i ostat] [,err]) [iolist]

Unformatted
REWRITE ( extu [, iostat] [,err] ) [io l ist]

Control-list parameters are symbolized as follows:

extu-a logical unit specifier
fmt-a format specifier

iostat-an I/O status specifier
err-a transfer-of-control specifier
The I/O list parameter is symbolized as follows:

iolist-an I/0-list specifier
The parameters used in I/O statements are described in Sections 7.1.1
(control-list parameters) and 7.1.2 (I/0-list parameter). The rules for
specifying control-list parameters are summarized in Section 7.1.1.1.

1/0 Statements 7-45

7.4. 1 Formatted REWRITE Statement
The formatted REWRITE statement performs the following operations:
•

Retrieves binary values from internal storage.

•

Translates those values to character form using format specifiers to
provide editing.

•

Writes the translated data to an existing record in a file with indexed
or relative organization.

The formatted REWRITE statement writes to the current record in the
file (the last record accessed by a preceding direct access, indexed, or
sequential READ statement).
Errors occur with the following conditions:
•

If the primary key value is changed, an error usually occurs.

•

If you attempt to rewrite more than one record in a single REWRITE
statement operation, an error occurs.

•

If a record is too long, an error occurs. (A record might become too
long when unused space in a rewritten fixed -length record is filled
with spaces. )

Example
In the following example, the REWRITE statement updates the current
record contained in the indexed organization file connected to logical
unit 3 with the values represented by NAME, AGE, and BIRTH.
10

7.4.2

REWRITE (3 , 10,ERR=99) NAME , AGE , BIRTH
FORMAT (A16,I 2 ,A8)

Unformatted REWRITE Statement
The unformatted REWRITE statement retrieves binary values from internal
storage and writes those values to an existing record in a file with indexed
or relative organization. The values are not translated.
The unformatted REWRITE statement writes to the current record in the
file (the last record accessed by a preceding indexed or sequential READ
statement). Unused space in a rewritten fixed-length record is filled with
zeros.

7-46

1/0 Statements

Errors occur with the following conditions:

•
•

•

If the primary key value is changed, an error usuall y occurs .

If you attempt to rewrite more than one record in a single REWRITE
statement operation, an error occurs.
If a record is too long, an error occurs .

7.5 ACCEPT Statement
The ACCEPT statement transfers input data to internal storage from
external records accessed under the sequential mode of access. ACCEPT
statements can only be used on implicitly connected logical units .
ACCEPT statements take any one of the following forms:
ACCEPT f[ , iolist]
ACCEPT * [ . iolist]
ACCEPT n

Control -list parameters are symbolized as follows :
/ - th e nonkeyword form of a format specifier
*- a list-directed formatting specifier
n- the nonkeyword form of a namelist specifier
The 1/ 0 -list parameter is symbolized as follow s:

iolist-an I/O list specifier
The parameters used in I/O statements are described in Sections 7.1.1
(control-list parameters) and 7.1.2 (I/0-list parameter) . The rules for
specifying control-list parameters are summarized in Section 7.1.1.1.
The ACCEPT statement functions exactly like the sequential READ statements discussed in Sections 7.2.1.1 through 7.2.1.3, with the following
important exception: the ACCEPT statement can never be connected to
user-specified logical units .

1/0 Statements 7-47

Example

In the following example, th e ACCEPT statement reads character data
from the implicit unit and assigns binary values to each of the five
elements of the arra y CHARAR:

200

CHARACTER*10 CHARAR (5)
ACCEPT 200, CHARAR
FORMAT (5A10)

7.6 TYPE and PRINT Statements
The TYPE and PRINT statements transfer output data from internal
storage to external records that are sequentially accessed.
TYPE and PRINT statements take the same forms, which can be any one
of the following:
TYPE f [ , iolist]
PRI NT f [ , iolist]
TYPE * [ , iolist]
PRI NT * [ , iol i st]
TYPE n
PRI NT n

Control-list parameters are symbolized as follows:
f-the nonkeyword form of a format specifier
*-the list-directed formatting specifier
n-the nonkeyword form of a namelist specifier
The I/0-list parameter is symbolized as follows:

iolist-the I/0-list specifier
The parameters used in I/O statements are described in Sections 7.1.1
(control-list parameters) and 7.1.2 (I/0-list parameter).
TYPE and PRINT statements function exactly like the formatted sequential
WRITE statement discussed in Section 7.3.1.1, with the following important exception: the formatted sequential TYPE and PRINT statements can
never be used to transfer data to user-specified logical units.

7-48

I/0 Statements

Example
In the following example, the PRINT statement writes one record to the
implicit output device. The record has four fields of character data.

400

CHARACTER*16 NAME, JOB
PRI NT 400 , NAME , JOB
FORMAT
NAME= A. JOB=
( I

•

1/0 Statements

7-49

Chapter 8

1/0 Formatting
Formatting 1/0 statements specify the form of data being transferred.
They also specify the data conversion (editing) required to achieve that
form. The primary formatting statement is the FORMAT statement. It
is a nonexecutable statement used in coniunction with formatted 1/0
statements and with ASSIGN, ENCODE, and DECODE statements.
This chapter contains the following information about 1/0 formatting:
•
•

General rules for writing FORMAT statements (Section 8.1)
FORMAT statement syntax (Section 8.2)

•

Field and edit descriptors (Section 8.3)

•

Carriage control options for output records (Section 8.4)

•

Format specifications and field separators (comma and slash)
(Sections 8.5 and 8.6)

•

Run-time formats (instead of a FORMAT statement) that dynamically
creates formats during program execution (Section 8. 7)

•

Format control interactions with 1/0 lists (Section 8.8)

1/0 Formatting

8-1

8. 1 General Rules for Writing FORMAT Statements
This section summarizes the rules for constructing and using the format
specifications and their components in FORMAT statements. It also
svmmarizes the rules for constructing external fields and records .
The following are general FORMAT statement rules:

8-2

1/0 Formatting

•

A FORMAT statement must always be labeled.

•

In a field descriptor such as rlw[.m] or nX, the terms r, w, m, and n
must be unsigned integer constants or variable format expressions
whose values are greater than or equal to zero. The values of r
and w must be greater than zero and less than or equal to 32767,
and the values of m and n must be greater than zero and less than
or equal to 255. (They cannot be names assigned to constants in
PARAMETER statements.) You can omit the repeat count and field
width specification.

•

In a field descriptor such as Fw.d, the term d must be an unsigned
integer constant or variable format expression. You must specify d
with F, E, D, and G field descriptors even if d is zero. The decimal
point is also required. You must either specify both w and d, or omit
them both. In a field descriptor such as Ew.dEe, the term e must also
be an unsigned integer constant.

•

In a field descriptor such as nHclc2 ... en, exactly n characters must
follow the H format code. You can use any printable ASCII character
in this field descriptor.

•

In a scale factor of the form nP, n must be an integer constant or
variable format expression in the range -128 to 127. The scale factor
affects the F, E, D, and G field descriptors only. Once you specify
a scale factor, it applies to all subsequent real field descriptors in
that format specification until another scale factor appears. You
must explicitly specify OP to reinstate a scale factor of zero. Format
reversion does not affect the scale factor.

•

No repeat count is permitted in BN, BZ, S, SS, SP, H, Q, X, T, TR, TL,
$, :, or character constant field descriptors unless these descriptors are
enclosed in parentheses and treated as a group repeat specification.

•

If the associated I/O statement contains an I/O list, the format
specification must contain at least one field descriptor. This descriptor
must be I, 0, Z, F, E, D, G, L, A, or Q.

8.1.1

•

A format specification in a character variable, character substring reference, character array element, character array, character expression,
numeric array, or numeric array element must be constructed in the
same way as a format specification in a FORMAT statement, including
the opening and closing parentheses.

•

If a character-constant format includes apostrophes, those apostrophes
must be represented by double apostrophes (").

Input Rules for FORMAT Statements
The following are general FORMAT statement input rules:
•

A minus sign must precede a negative value in an external input field;
a plus sign is optional before a positive value.

•

On input, an external field under I field descriptor control must be an
integer constant. It cannot contain a decimal point or an exponent. An
external field under 0 field descriptor control must contain only the
numerals 0 through 7. An external field input under Z field descriptor
control must contain only the numerals 0 through 9 and the letters
A(a) through F(f). An external field under 0 or Z field descriptor
control must not contain a sign, a decimal point, or an exponent. You
cannot use octal and hexadecimal constants in the form '777'0 or
'AF9'X in external records .

•

On input, an external field under F, E, D, or G field descriptor control
must be an integer constant or a real constant. It can contain a decimal
point; an E(e), D(d), or Q(q) exponent field; or both.

•

If an external field contains a decimal point, the actual size of the
fractional part of the field, as indicated by that decimal point, overrides
the d specification of the corresponding real field descriptor.

•

If an external field contains an exponent, the scale factor (if any) of the
corresponding field descriptor is inoperative for the conversion of that
field.

•

The field width specification must be large enough to accommodate
both the numeric character string of the external field and any other
characters that are allowed (algebraic sign, decimal point, exponent, or
combination of the three).
A comma is the only character you can use as an external field
separator. It terminates the input of fields (for noncharacter data
types) that are shorter than the number of characters expected. It also
designates null (zero-length) fields.

•

1/0 Formatting

8-3

8.1.2

Output Rules for FORMAT Statements
The following are general FORMAT statement output rules:
•

•

A format specification cannot specify more output characters than the
external record can contain. For example, a line printer record cannot
contain more than 133 characters, including the carriage control
character.
The field width specification (w) must be large enough to accommodate all characters that the data transfer can generate, including an
algebraic sign, decimal point, and exponent. For example, the field
width specification in an E field descriptor should be large enough to
contain d+7 or d+e+S characters.
The first character of a record transmitted to a line printer or terminal
is typically used for carriage control; it is not printed. The first character of such a record should be a space, 0, 1, $, +, or ASCII NUL. Any
other character is treated as a space.

8.2 FORMAT Statement Syntax
The FORMAT statement takes the following form:
FORMAT (q1f 1s1f2s2 ... fnqn)

qn
Is zero or more slash ( /) record terminators. (See Section 8.5.)
fn
Is a field descriptor or a group of field descriptors enclosed in parentheses.
(See Section 8.3 .)

s
Is a field separator. (See Sections 8.5 and 8.6.)
The entire list of field descriptors and field separators, including the
parentheses, is called the format specification.

8-4 1/0 Formatting

The field descriptor takes one of the following forms:
[r] c
[r] cw
[r] cw . m
[r]cw.d[Ee]

r
Is the repeat count for the field descriptor. If you omit r, the repeat count
is assumed to be 1.

c
Is a format code (I, 0, Z, F, E, D, G, L, A, H, X, T, P, Q, $, :, BN, BZ, S,
SP, SS, TL, or TR).
w
Is the external field width, in characters.

m
Is the minimum number of characters that must appear within the field
(including leading zeros).

d
Is the number of characters to the right of the decimal point.

E
In this context, identifies an exponent field.

e
Is the number of characters in the exponent.
The r, w, m, and d terms must all be unsigned integer constants or
variable format expressions. The values of r and w must be greater than
zero and less than or equal to 32767, and the values of m, d, and e must
be greater than zero and less than or equal to 255.
The r term is optional with some field descriptors but invalid with others
(see Section 8.3.1).
The d and e terms are required with some field descriptor but invalid with
others.
PARAMETER constants cannot be used as values for the r, w, m, d, ore
specifiers.

1/0 Formatting

8-5

The field descriptors are as follows:
•

Integer-Iw, Ow, Zw, Iw.m, Ow.m, Zw.m

•

Logical-L w

•

Real and complex-Fw.d, Ew.d, Dw.d, Gw.d, Ew.dEe, Gw.dEe

•

Character-Aw

•

Editing, and character and Hollerith constants-nH, ' ... ', nX, Tn, TLn,
TRn, nP, Q, $, :, BN, BZ, S, SP, SS (n is the number of characters or
character positions).

Table 8-1 summarizes the FORMAT codes.

Table 8-1:

8-6

1/0 Formatting

FORMAT Code Summary

Code

Form

Effect

A[w]

Transfers character or Hollerith values. (See
Section 8.3.9.1.)

Specifies that embedded and trailing blanks in
a numeric input field are to be ignored. (See
Section 8.3.3.1.)

Specifies that embedded and trailing blanks in a
numeric input field are to be treated as zeros. (See
Section 8.3.3.2.)

Dw.d

Transfers real values (D exponent field indicator). (See
Sections 8.3.6.3 and 8.3 .6.5.)

Ew.d[Ee]

Transfers real values (E exponent field indicator) . (See
Sections 8.3 .6.2 and 8.3.6.5 .)

Fw.d

Transfers real values. (See Sections 8.3.6.2 and 8.3.6.5.)

Gw.d[Ee]

Transfers real values: on input, acts like F code; on
output, acts like E code or F code, depending on the
magnitude of the value. (See Sections 8.3.6.4 and
8.3.6.5.)

nHc. ..c

Transfers data between the H field descriptor and an
external record. (See Section 8.3.9.2.)

Iw[.m]

Transfers decimal integer values. (See Section 8.3.5 .1.)

Transfers logical data: on input, transfers characters; on
output, transfers T or F. (See Section 8.3.8.)

Ow[.m]

Transfe rs octal values. (See Section 8.3.5 .2.)

Table 8-1 (Cont.):

FORMAT Code Summary

Code

Form

Effect

Alters locations of decimal points. (See Section 8.3.7.)

Obtains the num.ber of characters remainin g to be
transferred in an input record. (See Section 8.3.12.1.)

Reinvokes optional plus characters in numeric output fields; counters the action of SP and SS. (See
Section 8.3.4.3.)

Writes plus characters that would otherwise be optional
into numeric output fields. (See Section 8.3.4.1.)

Suppresses optional plus characters in numeric output
fields. (See Section 8.3.4.2.)

Specifies positional tabulation . (See Section 8.3.11.2.)

TLn

Specifies relative tabulation (left). (See Section 8.3.11.3.)

TRn

Specifies relative tabulation (right). (See Section 8.3.11.4.)

Specifies that n characters are to be skipped. (See
Section 8.3.11.1.)

Zw[ .m]

Transfers hexadecimal values. (See Section 8.3.5.3.)

Suppresses carriage return during interactive 1/0. (See
Section 8.3.12.2.)
Terminates format control if the I/O list is exhausted.
(See Section 8.3.12.3.)

8.3 Field and Edit Descriptors
A field descriptor describes the size and format of one or more data items.
Each data item in the external medium is called an external field. An edit
descriptor specifies an editing function to be performed on a data item or
items.
The numeric field descriptors ignore leading spaces in the external field.
Embedded and trailing spaces are ignored only if the BN edit descriptor is
specified or if BLANK='NULL' is in effect for the logical unit. Otherwise,
embedded and trailing spaces are treated as zeros.

1/0 Formatting

8-7

At the beginning of the execution of each formatted input statement, the
BLANK attribute for the relevant logical unit determines the interpretation
of spaces. Default values are as follows:
•
•

BLANK= 'NULL'-when an open has been executed
BLANK = 'ZERO'-when no explicit open has been executed

During execution of a formatted input statement, the BN and BZ edit
descriptors may supersede the default interpretation of blanks. The BN
and BZ edit descriptors affect only the formatted 1/0 statement of which
they are a part (as do the S, SP, and SS edit descriptors).
Sections 8.3.3 through 8.3.12 describe each of the field and edit descriptors.

8.3.1

Repeat Counts and Group Repeat Counts
You can apply the field descriptors I, 0, Z, F, E, D, G, L, and A to a
number of successive data fields by preceding the field descriptor with an
unsigned integer constant (parameter constants not allowed) specifying the
number of repetitions. This constant is called a repeat count.
For example, the following two statements are equivalent:
20

FORMAT (E12 . 4,E12 .4,E12 .4,I5,I5 , I5,I5)

FORMAT (3E12 .4,4I5)

Similarly, you can apply a group of field descriptors repeatedly to data
fields by enclosing these field descriptors in parentheses and preceding them with an unsigned integer constant (parameter constants are
prohibited). The integer constant is called a group repeat count.
For example, the following two statements are equivalent:
50

FORMAT (2I8,3(F8 .3,E15 . 7) ,2(15))

FORMAT (I8,I8 , F8.3 ,E15 .7,F8 . 3,E15 .7,F8.3,E15.7,I5,I5)
1

An H or Q field descriptor, which could not otherwise be repeated, can be
enclosed in parentheses and treated as a group repeat specification. Thus,
it could be repeated a desired number of times.
If you do not specify a group repeat count, a default count of 1 is assumed.

Section 8.8 discusses how to use parentheses when the number of values
to be formatted is greater than the number of format specifications.
8-8

1/0 Formatting

8.3.2

Variable Format Expressions
By enclosing an arithmetic expression in angle brackets, you can use it
in a FORMAT statement wherever you can use an integer (except as the
specification of the number of characters in the H field); for example:
FORMAT (I <J +1 >)

When the format is scanned, the preceding statement performs an I (integer) data transfer with a field width of J+l. The expression is reevaluated
each time it is encountered in the normal format scan.
Syntax Rules

The following syntax rules apply to variable format expressions:
•

If the expression is not of integer data type, it is converted to integer
data type before being used.

•

The expression can be any valid FORTRAN expression, including
function calls and references to dummy arguments.

•

The value of a variable format expression must obey the restrictions
on magnitude applying to its use in the format, or an error occurs.
Variable format expressions are not permitted in run-time formats.

•

Variable format expressions are evaluated each time they are encountered
in the scan of the format. If the value of the variable used in the expression changes during the execution of the I/O statement, the new value is
used the next time the format item containing the expression is processed.
See Section 8.8 for a description of the synchronization of I/O lists with
formats .
Example

Consider the following statements:
DIMENSION A ( 5 )
DATA A/1 . , 2 . , 3 . , 4 . ,5 . /

100
10

DO 10 I=1 , 10
WRITE ( 6, 100 ) I
FORMAT ( I <MAX ( I,5 )> )
CO NTI NUE

1/0 Formatting

8-9

DO 20 I=l, 5
WRITE (6, 101) (A(I) , J=l, I)
FORMAT (<I>FlO.<I - 1>)
CONTI NUE
END

101
20

On execution, these statements produce the following output:
1
2
3
4

5
6
7

8
9

10
1.

2.0
3.00
4.000
5.0000

2.0
3 . 00
4.000
5.0000

3.00
4.000
5 . 0000

4.000
5.0000

5 0000

8.3.3 Blank Control Editing
The treatment of embedded and trailing blanks within numeric input files
is controlled by BN and BZ edit descriptors.
8 .3.3. 1

BN Edit Descriptor

The BN descriptor causes the processor to ignore all the embedded and
trailing blanks it encounters within a numeric input field. It takes the
following form:
BN

The effect is that of actually removing the blanks and right-justifying the
remainder of the field. A field of all blanks is treated as zero. The BN
descriptor affects only I, 0, Z, F, E, D, and G editing during the execution
of an input statement.

8-10 1/0 Formatting

8.3.3.2

BZ Edit Descriptor

The BZ descriptor causes the processor to treat all the embedded and
trailing blanks it encounters within a numeric input field as zeros. It takes
the following form:
BZ

The BZ descriptor affects only I, 0, Z, F, E, D, and G editing during the
execution of an input statement.

8.3.4 Sign Control Editing
The treatment of optional plus characters in output data is controlled by
SP, SS, and S edit descriptors.
8.3.4.1

SP Edit Descriptor

An SP descriptor causes the processor to produce a plus character (+) in
any position where this character would otherwise be optional. It takes
the following form:
SP

The SP descriptor affects only I, F, E, D, and G editing during the execution of an output statement.
8.3.4.2

SS Edit Descriptor

The SS descriptor causes the processor to suppress a leading plus character
from any position where this character would normally be produced as
an optional character. It has the opposite effect of the SP field descriptor
described previously. The SS descriptor takes the following form:
SS

The SS descriptor affects only I, F, E, D, and G editing during the execution of an output statement.

1/0 Formatting

8-11

8.3.4.3

S Edit Descriptor
The S edit descriptor reinvokes optional plus characters (+) in numeric
output fields. It takes the following form:

s
The S descriptor counters the action of either the SP or SS descriptor by
restoring to the processor the discretion of producing plus characters on an
optional basis.
The same restrictions apply as for the SP and SS descriptors.

8.3.5

Integer Editing
Integer editing is controlled by I (decimal), 0 (octal), and Z (hexadecimal)
field descriptors.

8.3.5. 1

I Field Descriptor
The I field descriptor transfers decimal integer values. It takes the following form:
Iw [ . m]

The corresponding 1/0 list element must have an integer or logical data
type .
Input Processing
In an input statement, the I field descriptor transfers w characters from
the external field and assigns them to the corresponding I/O list element
as an integer value. The external data must have the form of an integer
constant. It cannot contain a decimal point or exponent field.
The I field descriptor processes input in the following ways:

8-12

•

If the value of the external field exceeds the range of the corresponding list element, an error occurs.

•

If the first nonblank character of the external field is a minus sign, the
field is treated as a negative value.

1/0 Formatting

•

If the first nonblank character is a plus sign or if no sign appears in
the field, the field is treated as a positive value.

•

If the field is blank, it is treated as a value of zero.

The following list illustrates valid input processing with the I field descriptor:
Format

External Field

Internal Value

2788

-26

MMM312

312

Output Processing

In an output statement, the I field descriptor transfers the value of the
corresponding I/O list element, right-justified, to an external field that is
w characters long.
The I field descriptor processes output in the following ways:
•

If the value does not fill the field, leading spaces are inserted.

•

If the value is too large for the field, the entire field is filled with
asterisks.

•

If the value of the list element is negative, the field will have a minus
sign as its leftmost, nonblank character. Therefore, the term w must
be large enough to fit a minus sign when necessary.

•

If m is present, the external field consists of at least m digits and is
filled with zeros on the left, if necessary.

The following list illustrates valid output processing with the I field
descriptor:

1/0 Formatting

8-13

Format

Internal Value

External Representation

284

-284

tiMO

174

M174

3244

-473

**
***

29 .812

(Not permitted: error)

14.0

14.2

M01

14.4

0001

If m is zero and the internal representation is zero, the external field is
blank.

8.3.5.2

0 Field Descriptor
The 0 field descriptor transfers octal (base 8) values and can be used with
any da ta type. It takes the following form :
Ow [ . m]

Input Processi ng

In an input statement, the 0 field descriptor transfers w characters from
the external field and assigns them as an octal value to the corresponding
I/O list element. The external field can contain only the numerals 0
through 7. It cannot contain a sign, a decimal point, or an exponent field .
An all-blan k field is treated as a value of zero. An error occurs if the value
of the external field exceeds the range of the corresponding list element.
The following list illustrates valid input processing using the 0 field
descriptor:

8-14 1/ 0 Formatting

Format

External Field

Internal Octal Value

32767

16234

1623

97t::.

(Not pe rmitted : error)

Output Processing

In an outpu t statement, the 0 field descriptor transfers the octal value
of the corresponding I/O list element, right-justified, to an external field
that is w characters long. No signs are transmitted; a negative value is
transmitted in internal form.
If the value does not fill the field, leading spaces are inserted; if the value
is too large for the field, the entire field is filled with asterisks. If m is
present, the external field consists of at least m digits and is zero-filled on
the left if necessary.

The following list illustrates valid output processing using 0 field descriptors :
Format

Internal (Decimal) Value

External Representation

32767

t::.77777

-32767

100001

14261

M33

10 . 5

41050

04.2

M07

04.4

0007

If m is zero and the external representation is zero, the external field is
filled with blanks .

1/0 Formatting

8-15

8 .3 .5.3

Z Field Descriptor
The Z field descriptor transfers hexadecimal (base 16) values, and can be
used with any data type. It takes the follo wing fo rm:
Zw [ m]

Input Processing

In an input statem ent, the Z field descriptor transfers w characters from
the external fiel d and assigns them as a h exadecimal value to the corresponding 1/0 list element. The external field can contain only the
numerals 0 through 9 and the letters A (a) through F (f) . It cannot contain
a sign, decimal point, or exponent fi eld.
An all-blank field is treated as a value of zero. If the value of the external
field exceeds the range of the corresponding list element, an error occurs.
The following list illustrates valid input processing using the Z field
descriptor:
Format

External Field

Intern al Hexadecimal Value

A94

A23DEF

A23DE

95 .AF2

(Not permitted: error)

A94

Output Processing

In an output statement, the Z field descriptor transfers the hexadecimal
value of the corresponding 1/0 list element, right-justified, to an external
field that is w characters long. No signs are transmitted. A negative value
is transmitted in internal form.
If the value does not fill the field, leading spaces are inserted; if the value
is too large for the field, the entire field is filled with asterisks. If m is
present, the external field consists of at least m digits and is filled with
zeros on the left, if necessary.

The following list illustrates valid output processing using the the Z field
descriptor:

8-16

1/0 Formatting

Format

Internal (Decimal) Value

External Representation

32767

-32767

- 10 . 5

C228

Z3.3

2708

A94

Z6.4

2708

M OA94

7FFF

68001

If m is zero and the internal representation is zero, the external field is
filled with blanks.

8.3.6

Real Editing
Editing performed on data with a real data type is controlled by the F, E,
D, and G field descriptors.
NOTE
When attempting to parse textual input, you should not mix F,
E, D, or G format descriptors. These descriptors accept some
forms that are purely textual as valid numeric input values. For
example, the input values D, E, El, +, - , and . are all treated
as 0.0.

8.3.6. 1

F Field Descriptor

The F field descriptor transfers real values. It takes the following form:
Fw.d

The corresponding I/O list element must have a real data type or it must
be either the real or the imaginary part of a complex data type .
Input Processing

In an input statement, the F field descriptor transfers w characters from
the external field and assigns them as a real value to the corresponding
1/0 list element.

1/0 Formatting

8-17

Input processing with the F field descriptor behaves in the following ways:
•

If the first nonblank character of the external field is a minus sign, the
field is treated as a negative value.

•

If the first nonblank character is a plus sign or if no sign appears in
the field, the field is treated as a positive value.

•

If a field is all blank, it is treated as a zero value.

•

If a field contains only an exponent or decimal point, it is treated as a
zero value.

•

If the field contains neither a decimal point nor an exponent, it is
treated as a real number of w digits, in which the rightmost d digits
are to the right of the decimal point, with leading zeros assumed, if
necessary.

•

If the field contains an explicit decimal point, the location of that
decimal point overrides the location specified by the field descriptor.
If the field contains an exponent, that exponent is used to establish the
magnitude of the value before it is assigned to the list element.

The following list illustrates valid input processing using the F field
descriptor:
Format

External Field

Internal Value

F8.5

123456789

123 . 45678

F8.5

-1234.567

-1234 .56

F8.5

24.77E+2

2477 . 0

FS .2

1234567.89

123.45

Output Processing

In an output statement, the F field descriptor transfers the value of the
corresponding 1/0 list element, rounded to d decimal positions and
right-justified, to an external field that is w characters long.
If the value does not fill the field, leading spaces are inserted; if the value
is too large for the field, the entire field is filled with asterisks .

The term w must be large enough to include all of the following:
•

8-18 1/0 Formatting

Minus sign when necessary (plus signs are optional)

•

At least one digit to the left of the decimal point

•

Decimal point

•

d digits to the right of the decimal

In other words, w must be greater than or equal to d+3.
The following list illustrates valid output processing using the F field
descriptor:
Format

Internal Value

F8.5

8.3.6.2

2 . 3547188

External Representation
ti2 . 35472

F9 .3

8789.7361

F2 .1

51 . 44

Fl0.4

- 23 . 24352

M-23 . 2435

FS .2

325.01 3

******

FS .2

- .2

-0 . 20

ti8789 . 736

E Field Descriptor

The E field descriptor transfers real values in exponential form. It takes
the following form:
Ew . d [Ee]

The corresponding 1/0 list element must have a real data type or it must
be either the real or the imaginary part of a complex data type.
Input Processing

In an input statement, the E field descriptor transfers w characters from
the external field and assigns them as a real value to the corresponding
1/0 list element. The F field descriptor interprets and assigns data in
exactly the same way.
The following example illustrates valid input processing using the E field
descriptor:

1/0 Formatting

8-19

Format

External Field

Internal Value

E9.3

734 .432E3

734432.0

El2.4

M1022 . 43E-6

ElS .3

52 . 3759663MMli

52 . 3759663

El2 .5

210 . 52710+10

210.5271E10

1022 . 43E-6

In the last example, the E field descriptor treats the D exponent field
indicator as an E indicator if the I/O list element is single precision.
Output Processing

In an output statement, the E field descriptor transfers the value of
the corresponding I/O list element, rounded to d decimal digits and
right-justified, to an external field that is w characters long.
If the value does not fill the field, leading spaces are inserted. If the value
is too large for the field, the entire field is filled with asterisks.

When you use the E field descriptor, data output is transferred into
standard form. The standard form has the following components:

•

•
•
•

•

Minus sign, when necessary (plus signs are optional)
Zero
Decimal point
d digits to the right of the decimal point
e + 2-character exponent that takes one of the following forms :
For exponents less than or equal to 99, with Ew . d:
E+nn
E-nn

For exponents less than or equal to 999, with Ew . d:
+nnn
-nnn

For all exponents with Ew . dEe:
E+n1n2 ... ne
E-n1n2 ... ne

8-20

1/ 0 Formatting

The exponent field width specification is optional. If you omit it, the value
of e defaults to two. If the exponent value is too large to be converted into
one of the preceding forms, an error occurs.
The d digits to the right of the decimal point represent the entire value,
scaled to a decimal fraction .
The term w must be large enough to include all of the following :
•

Minus sign when necessary (plus signs are optional)

•

Zero

•
•

Decimal point
d digits

•

Exponent

In other words, w must be greater than or equal to d+7. If e is present, w
must be greater than or equal to d+e+S.
The following list illustrates valid output processing using the E field
descriptor:
Format

Internal Value

E9.2

475867.222

l!.0 .48E+06

E12.5

475867 . 222

l!.0 .47587E+06

E12.3

8.3.6.3

0 . 00069

External Representation

l!.M0 . 690E-03

EI0.3

-0 . 5555

- 0 .556E+OO

ES.3

56 . 12

*****

E14.5E4

-1 . 001

-0 . 10010E+0001

E14.3E6

0 . 000123

l!.0 . 123E-000003

D Field Descriptor
The D field descriptor transfers real values in exponential form. It takes
the following form:
Dw.d

The corresponding I/O list element must have a real data type or it must
be either the real or the imaginary part of a complex data type.

1/0 Formatting

8-21

Input Processing

In an input statement, the D field descriptor transfers w characters from
the external field and assigns them as a real value to the corresponding
I/O list element. The F and E field descriptors interpret and assign data in
exactly the same way.
The following list illustrates valid input processing using the D field
descriptor:
Format

External Field

Internal Value

BZ,010.2

12345MMti

12345000.000

010.2

M123 .45M

015.3

367 . 49817630+04

123 . 4500
3.6749817630+06

Output Processing

In an output statement, the D field descriptor has the same effect as the E
field descriptor, except that the D exponent field indicator is used in place
of the E indicator.
The following list illustrates valid output processing using the D field
descriptor:

8.3.6.4

Format

Internal Value

014.3

0 . 0363

023.12

5413 .87625793

09.6

1.2

External Representation
MtiM0 . 3630-01
tititititi0.5413876257930+04

** *******

G Field Descriptor
The G field descriptor transfers real values in a form that, in effect,
combines the F and E field descriptors. It takes the following form:
Gw.d[Ee]

The corresponding I/O list element must be of real data type, or it must
be either the real or the imaginary part of a complex data type.

8-22

1/0 Formatting

Input Processing

In an input statement, the G field descriptor transfers w characters from
the external field and assigns them as a real value to the corresponding
I/O list element. The F, D, and E field descriptors interpret and assign
data in exactly the same way.
Output Processing

In an output statement, the G field descriptor transfers the value of the
corresponding 1/0 list element, rounded to d decimal positions and
right-justified, to an external field that is w characters long. The form in
which the value is written is a function of the magnitude of the value, as
described in Table 8-2.
Table 8-2: Effect of Data Magnitude on G Format Conversions
Data Magnitude

Effective Conversion

m .LT. 0.1

Ew.d[Ee]

0.1 .LE. m .LT. 1.0

F(w-4).d, n (' ')

1.0 .LE. m .LT. 10.0

F(w-4).(d-1), n (' ')

lO**d-2 .LE. m .LT. lO**d-1

F(w-4).1 , n(' ')

lO**d-1 .LE . m .LT. lO**d

F(w-4).0, n(' ')

m .GE. lO**d

Ew.d[Ee]

The n(' ') field descriptor, which is in effect, inserted by the G field
descriptor for values within its range, specifies that four or e+2 spaces are
to follow the numeric data representation.
The term w must be large enough to include all of the following:
•
•

Minus sign when necessary (plus signs are optional)
Decimal point

•

One digit to the left of the decimal point

•

d digits to the right of the decimal point

•

Either a 4-character or e+2-character exponent

1/0 Formatting

8-23

In other words, w must be greater than or equal to d+8. If e is present, w
must be greater than or equal to d+e+6.
The following list illustrates valid output processing using the G field
descriptor:
Format

Internal Value

External Representation

G13.6

0.01234567

/:!,.0.123457E - 01

G13.6

-0 . 12345678

-0 . 123457MM

G13.6

1 . 23456789

M1.23457MM

G13 .6

12 . 34567890

M12.3457MM

G13.6

123 . 45678901

M123 .457MM

G13.6

-1234.56789012

/:!,.-1234.57MM

G13.6

12345 . 67890123

M12345. 7MM

G13.6

123456 . 78901234

M123457 . MM

G13.6

-1234567.89012345

-0. 123457E+07

The following list shows the same values output-processed as the previous
list, except the following list uses an equivalent F field descriptor:
Format

Internal Value

External Representation

F13.6

0.01234567

/:!,.MMO . 012346

F13 .6

-0 . 12345678

MM-0 . 123457

F13.6

1 . 23456789

MMf!.1 . 234568

F13.6

12.34567890

MM12.345679

F13 .6

123.45678901

MM23. 456789

F13.6

-1234.56789012

/:!,.-1234 . 567890

F13 .6

12345 . 67890123

!:!,.12345. 678901

F13.6

123456 . 78901234

123456.789012

F13.6

-1234567.89012345

********** ***

8-24 1/0 Formatting

8.3.6.5

Complex Data Editing

A complex value is an ordered pair of real values. Therefore, input or
output of a complex value is governed by two real field descriptors, using
any combination of the forms Fw.d, Ew.dEe, Dw.d, or Gw .dEe.
Input Processing

In an input statement, the two successive fields are read and assigned to a
complex I/O list element as its real and imaginary parts, respectively.
The following list illustrates valid input processing using complex data
editing:
Format

External Field

Internal Value

F8.5,F8 .5

1234567812345.67

123 . 45678, 12345.67

E9 .1,F9 .3

734.432E8123456789

734 . 432£8, 123456 . 789

Output Processing

In an output statement, the two parts of a complex value are transferred
under the control of repeated or successive field descriptors . The two parts
are transferred consecutively without punctuation or spacing unless the
format specifier states otherwise.
The following list illustrates valid output processing using complex data
editing.
Format

Internal Value

External Representation

2F8 .5

2.3547188, 3 . 456732

~2.35472

E9.2,' ti ,ti ',ES.3

47587 . 222, 56 . 123

~0 . 48E+06ti,L'I *****

1'13.45673

8.3. 7 Scale Factor Editing-P Edit Descriptor
During either input or output processing, the scale factor lets you alter
the location of the decimal point in real values and in the two parts of
complex values. The scale factor takes the following form:
nP

-1/0 Formatting

8-25

n
Is a signed or unsigned integer constant in the range -128 through 127.
It specifies the number of positions, to the left or right, that the decimal

point is to move.
A scale factor can appear anywhere in a format specification but it must
precede the first field descriptor that associates with it; for example:
nPFw .d

nPEw.d

nPDw .d

nPGw . d

Input Processing

On input, the scale factor associated with an F, E, D, or G field descriptor
multiplies the data by 10**-n and assigns it to the corresponding I/O
list element. For example, a 2P scale factor multiplies an input value by
.01, moving the decimal point two places to the left. A -2P scale factor
multiplies an input value by 100, moving the decimal point two places to
the right. However, if the external field contains an explicit exponent, the
scale factor has no effect.
The following list illustrates valid input processing using scale factor
editing:

Format

External Field

Internal Value

3PE10 .5

f1.M37 . 614f1.

3PE10.5

M37.614E2

3761 . 4

-3PE10 .5

MM37 . 614

37614 . 0

. 037614

Output Processing

On output, the effect of the scale factor depends on the type of field
descriptor associated with it. For the F field descriptor, the value of the
I/O list element is multiplied by lO**n before transfer to the external
record. Thus, a positive scale factor moves the decimal point to the right.
A negative scale factor moves the decimal point to the left.
For the E or D field descriptor, the basic real constant part of the I/O list
element is multiplied by lO**n, and n is subtracted from the exponent. For
a positive scale factor, n must be less than (d + 2) or an output conversion
error occurs. Thus, a positive scale factor moves the decimal point to
the right and decreases the exponent. A negative scale factor moves the
decimal point to the left and increases the exponent.

8-26

1/ 0 Formatting

The following list illustrates valid output processing using scale factor
editing:
Format

Internal Value

External Representation

1PE12.3

-270 . 139

M-2 . 701E+02

1PE12.2

- 270 . 139

Mfl-2 .70E+02

-1PE12.2

- 270 . 139

flM-0 . 03E+04

The effect of the scale factor for the G field descriptor is suspended if the
magnitude of the data to be output is within the effective range of the
descriptor, because the G field descriptor supplies its own scaling function.
The G field descriptor functions as an E field descriptor if the magnitude
of the data value is outside its range. In this case, the scale factor has the
same effect as for the E field descriptor.
On input and on output under F field descriptor control, a scale factor
actually alters the magnitude of the data. On output, a scale factor under
E, D, or G field descriptor control merely alters the form in which the
data is transferred. In addition, on input, a positive scale factor moves the
decimal point to the left and a negative scale factor moves the decimal
point to the right. On output, the effect is the reverse.

If you do not specify a scale factor with a field descriptor, a default scale
factor of zero is assumed . However, once you specify a scale factor, it
applies to all subsequent real field descriptors in the same FORMAT
statement, unless another scale factor appears. For example, consider the
following statements:

100

DI MENSION A(6)
DO 10 I=1 , 6
A(I) = 25 .
TYPE 100 , A
FORMAT(' , F8 . 2 . 2PF8 . 2 , F8 . 2)
I

These statements produce the following results:
25 . 00 2500.00 2500 . 00
2500 . 00 2500 .00 2500 . 00

If a second scale factor appears in the FORMAT statement, it takes control
from the first scale factor.
Format reversion has no effect on the scale factor (see Section 8.8). A scale
factor of zero can be reinstated only by an explicit OP specification.

1/0 Formatting

8-27

8.3.8

Logical Editing-L Edit Descriptor
The L field descriptor transfers logical data. It takes the following form:
Lw

The corresponding I/O list element must have an integer or logical data
type.
Input Processing

In an input statement, the L field descriptor transfers w characters from
the external field in the following ways:
•

If the first nonblank characters of the field are T, t, .T, or .t, the value
.TRUE. is assigned to the corresponding 1/0 list element.

•

If the first nonblank characters are F, f, .F, or .f, the value .FALSE. is
assigned.

•

If the field contains all blanks, the value .FALSE. is assigned.

•

If any other value is in the external field, an error occurs.

The logical constants .TRUE. and .FALSE. are acceptable input forms.
Output Processing

In an output statement, the L field descriptor transfers either the letter T
(if the value of the corresponding 1/0 list element is .TRUE.) or the letter
F (if the value is .FALSE.) to an external field that is w characters long.
The letter T or F is in the rightmost position of the field, preceded by w-1
spaces.
The following list illustrates valid output processing using logical editing:

8-28

Format

Internal Value

. TRUE .

. FALSE .

1/ 0 Formatting

External Representation

8.3.9

Character Editing
Editing data with a character data type is controlled by the A and H field
descriptors .

8.3.9.1

A Field Descriptor

The A field descriptor transfers character or Hollerith values. It takes the
following form:
A[w]

The corresponding 1/0 list element can have any data type. If it has a
character data type, character data is transmitted. If it has any other data
type, Hollerith data is transmitted.
The value of w must be less than or equal to 32767.
Input Processing

In an input statement, the A field descriptor transfers w characters from
the external record and assigns them to the corresponding 1/0 list element. The maximum number of characters that can be stored depends
on the size of the 1/0 list element. For character 1/0 list elements, the
size is the length of either the character variable, the character substring
reference, or the character array element.
For n umeric 1/ 0 list elements, the size depends on the data type, as listed
in Table 8- 3.

1/0 Formatting

8-29

Table 8 - 3:

Size Lim it of Numeric Elements Using the A Field
Descriptor

1/0 List Element

Maxim um Number of Characters

BYTE

LOGICAL*l

LOGICAL*2

LOGICAL*4

INTEGER*2

INTEGER*4

REAL

REAL*8(DOU BLE PRECISION)

REAL*16
COMPLEX

16
81

COMPLEX*16(DOU BLE COMPLEX)

16 1

Becau se complex val ues are treated as pairs of rea l numbers, comp lex data ed iting req uires
two format codes. See Section 8.3.6.5.

If w is greater than the maximum number of characters that can be stored
in the corresponding 1/0 list element, only the rightmost characters are
assigned to that element. The leftmost excess characters are ignored.
If w is less than the number of characters that can be stored, w characters
are assigned to the list element, left-justified, and trailing spaces are added
to fill the element.

The following list illustrates valid input processing using the A field
descriptor:

8-30 1/0 Formatting

Format

External Field

Internal
Representation

Data Type

PAGEL'i#

CHARACTER*l

PAGEL'i#

El'l#

CHARACTER*3

PAGEL'i#

CHARACTER*6

PAGEL'i#

PAGEL'i#M

CHARACTER*8

PAGEL'i#

LOG ICAL*l

PAGEL'i#

ll#

INTEGER*2

PAGEL'i#

GEM

REAL

PAGEL'i#

PAGEL'i#M

REAL*8

Output Processing

In an output statement, the A field descriptor transfers the contents of
the corresponding I/O list element to an external field w characters long.
If w is greater than the list element size, the data appears in the field,
right-justified, with leading spaces. If w is less than the list element, only
the leftmost w characters are transferred.
The following list illustrates valid output processing using the A field
descriptor:
Format

Internal Value

External Representation

OHMS

L'iOHMS

VOLTS

AMPERES

AMP ER

If you omit w in an A field descriptor, a default value is supplied.
If the 1/0 list element has a character data type, the default value is the
length of the I/O list element. If the I/ O list element has a numeric data
type, the default value is the maximum number of characters tha t can be
stored in a variable of that data type.

1/0 Formatting

8-31

8.3.9.2

H Field Descriptor

The H field descriptor transfers data between the external record and the
H field descriptor itself. It has the form of a Hollerith constant:
nHc1c2c3 ... en

n
Is the number of characters to be transferred.

c
Is an ASCII character.
Input Processing

In an input statement, the H field descriptor transfers n characters from
the external field to the field descriptor. The first character appears
immediately after the letter H . Any ch aracters in the field descriptor before
input are replaced by the input characters.
Output Processing

In an output statement, the H field descriptor transfers n characters
following the letter H from the field descriptor to the external field.
8.3.9.3

Character Constants

You can use a character constant instead of an H field descriptor. Both
types of format specifier function identically.
In a character constant, the apostrophe is written as two apostrophes; for
example:
50

FORMAT ( ' TODAY' 'SllDATEtilS : ll' ,I2, '/' ,I2 , '/' ,I2)

When you use a pair of apostrophes this way, they count as a single
character.

8- 32

1/ 0 Formatting

8.3. 10

Default Field Descriptors
If you write the field descriptors I, 0, Z, L, F, E, D, G, or A without
specifying a field width value, default values for w, d, and e are supplied
based on the data type of the I/O list element.

Table 8-4 lists the default values for w, d, and e.
Table 8-4: Default Field Descriptor Values
List Element
w
Field IJescriptor

I,O,Z

BYTE

I,O,Z

INTEGER*2,LOGICAL*2

1,0,Z

INTEGER*4,LOGICAL*4

O,Z

REAL*4

O,Z

REAL*8

O,Z

REAL*16

LOGICAL

F,E,G,D

REAL, COMPLEX*8

F,E,G,D

REAL*8, COMPLEX*16

F,E,G,D

REAL*16

LOGICAL*l

LOG ICAL*2,INTEGER*2

LOGICAL*4,INTEGER*4

REAL*4, COMPLEX*8

REAL*8, COMPLEX*16

REAL*l6

CHARACTER*n

For the A field descriptor, the default is the actual length of the corresponding I/O list element.

1/0 Formatting

8-33

8.3. 11

Positional Editing
Positional editing is controlled by the X, T, TL, and TR edit descriptors.
On output, a T, TL, TR, or X edit descriptor does not by itself cause
characters to be transmitted and therefore does not by itself affect the
length of the record. If characters are transmitted to positions at or after
the position specified by a T, TL, TR, or X edit descriptor, positions
skipped and not previously filled are filled with blanks. The result is as if
the entire record were initially filled with blanks.

8.3. 11. 1

X Edit Descriptor
The X edit descriptor is a positional specifier. It takes the following form:
nX

The term n specifies how many character positions are passed over. The
value of n must be greater than or equal to one.
Input Processing

In an input statement, the X field descriptor specifies that the next n
characters in the input record are skipped.
Output Processing

In an output statement, the X field descriptor tabs right n spaces. It does
not write over anything already written on the same record; for example:
90

WRITE (6 ,90) NPAGE
FORMAT (' 1PAGE6NUMBER6 ' , I2 , 16X, 'GRAPHIC6ANALYSIS ,6CONT. ')

The preceding WRITE statement would print a record similar to the
following output:
PAGE NUMBER nn

GRAPHIC ANALYSIS , CONT.

The term nn is the current value of the variable NP AGE. The numeral 1 in
the first character constant is not printed; it is used to advance the printer
paper to the top of a new page. (Section 8.4 describes printer carriage
control.)

8-34 1/0 Formatting

A trailing X format on a record does not write any characters unless it is
followed by another field that does; for example:
WRITE (6 ,99) K
FORMAT ('t:.K=' , I6,5X)

The preceding example writes a record of only 9 characters. To cause n
trailing blanks to be written at the end of a record, use the format n(' t:.').
8.3. 11.2

T Edit Descriptor

The T edit descriptor is a positional tabulation specifier. It takes the form:
Tn

The term n indicates the character position of the external record. The
value of n must be greater than or equal to one.
Input Processing

In an input statement, the T field descriptor positions the external record
to its nth character position. For example, if an input statement reads a
record containing ABCMt:.XYZ, and this record is controlled by the following
format statement:
10

FORMAT (T7 ,A3,T1,A3)

On execution, the input statement would first read the characters XYZ and
then read the characters ABC.
Output Processing

In an output statement, the T field descriptor specifies that subsequent
data transfer begins at the nth character position of the external record.
The first position of a record to be printed is usually reserved for a carriage
control character, which is not printed (see Section 8.4). For example:
25

PRINT 25
FORMAT (T51 , 'COLUMN 2' ,T21 , 'COLUMN 1')

These statements print the following line (assuming normal carriage
control processing):
Position 20

Position 50

+
COLUMN
1

COLUMN 2

•

1/0 Formatting

8-35

8.3. 11.3

TL Edit Descriptor
The TL edit descriptor is a relative tabulation specifier. It takes the
following form:
TLn

n
Indicates that the next character to be transferred to or from a record is the
nth character to the left of the current character. The value of n must be
greater than or equal to one. If the value of n is greater than or equal to
the current character position, the first character in the record is specified.

8.3. 11.4

TR Edit Descriptor
The TR edit descriptor is also a relative tabulation specifier. It takes the
following form:
TRn

n
Indicates that the next character to be transferred to or from a record is the
nth character to the right of the current character. The value of n must be
greater than or equal to one.

8.3.12 Additional Editing Operations
Additional edit descriptors are Q, dollar sign ($), and colon (:).
•
•
•

8-36

1/0 Formatting

The Q edit descriptor obtains the n umber of characters remaining
following a partial read operation.
The $ edit descriptor controls carriage returns .
The : edit descriptor terminates format control if no more items are in
the 1/0 list.

8 .3. 12 . 1

Q Edit D e scriptor

Th e Q edit descriptor obtains the number of ch aracters in the in put record
remaining to be transferred duri ng a read operation . It takes the form :
Q

The corresponding I/O list element must be of integer or logical data type;
for example:
READ (4 , 1000 ) XRAY , KK , NCHRS, (ICHR (I) , I= 1 , NCHRS)
1000 FORMAT (E1 5 . 7 , I 4 ,Q,80A1)

The preceding input statements read two fields into the variables XRAY
and KK. Th e number of characters remaining in th e record is stored in
NCHRS, and exactly that many characters are read into the array ICHR.
By placing the Q descriptor first in the format specification, you can
determine the actual length of the input record .
In an ou tput statement, the Q edit descriptor has no effect except that the
correspond ing I/O list element is skipped.

8 .3. 12.2

Dollar Sign D escript or
The dollar sign character ($) in a format specification modifies the carriage
control specified by the first character of the record. It only affects those
files for w h ich th e 'FORTRAN ' carriage control attribute is in effect (see
Section 8.4).
In an input statement, the $ descriptor is ignored.
In an output statement, if the first character of the record is a space, the
$ descriptor suppresses the carriage return. For terminal I/ O, this mean s
that a typed response will follow the output on the same line. If the first
character of the record is a plus sign, the $ descriptor causes the ou tput to
begin at the end of the previous line and leaves the prin t position at the
end of the line . If the first character of the record is 0 or 1, the $ descriptor
is ignored .
Consider the following statements:
100
200

TYPE 100
FORMAT ( ' ENTER RADI US VALUE ', $)
ACCEPT 200 , RADIUS
FORMAT (F6 . 2)

1/0 Formatting

8-37

The resulting formatted message would appear as follows :
ENTER RAD IUS VALUE

Your response (for example, "12.") can then go on the same line:
ENTER RAD IUS VALUE

8.3.12.3

12 .

Colon Descriptor

In a format specification, the colon character (:) terminates format control
if no more items are in the I/O list. The : descriptor has no effect if I/O
list items remain; for example:

1
2

PRI NT 1 ,3
PRI NT 2,4
FORMAT (' I=' , I2 . ' J=' . I2)
FORMAT (' K=' ,I2, : . I L=' ,I2)

These statements print the following two lines:
I=ti3LU=
K=M

Section 8.8 describes format control in detail.

8.4 Carriage Control
Whenever the default for the OPEN statement's CARRIAGECONTROL
keyword is in effect ('FORTRAN'), the first character of every record is
not printed when it is transferred to a printer. Instead, it is interpreted
as a carriage control character (except when overridden by the OPEN
statement keyword CARRIAGECONTROL = 'LIST' or 'NONE '). The
I/O system recognizes certain characters as carriage control characters.
Table 8-5 lists these characters and their effects.

8-38 1/0 Formatting

Table 8-5:

Carriage Control Characters

Character

Meaning

Overprinting: starts output at the beginning of the current line
and returns to the left margin after printing

t..

Single spacing: starts output at the beginning of the next line

Double spacing: skips a line before starting output

Paging: starts output at the top of a new page

Prompting: starts output at the beginning of th e next line and
suppresses carriage return at the end of the line

ASCII NUL

Overprinting with no advance : starts output at the beginning
of the current line and does not return to the left margin after
printing

Any character other than those listed in Table 8-5 is treated as a space
and is deleted from the print line. If you accidentally omit the carriage
control character, the first character of the record is not printed.

8.5

Format Specification Separators
Field descriptors in a format specification are generally separated by
commas. You can also use the slash (/) record terminator to separate field
descriptors. A slash terminates input or output of the current record and
initiates a new record; for example:
40

WRITE (6 ,40) K,L,M,N,O , P
FORMAT (3I6 . 6/I6,2F8 .4)

The preceding statements are equivalent to the following statements:
40
50

WRITE (6,40) K, L, M
FORMAT (3I6.6)
WRITE (6,50) N,O,P
FORMAT (I6,2F8 . 4)

Multiple slashes cause input records to be bypassed or blank records to be
outputted. If n consecutive slashes appear between two field descriptors,
(n-1) records are skipped on input, or (n-1) blank records are output. The
first slash terminates the current record. The second slash terminates the
first skipped or blank record, and so on.

1/0 Formatting

8-39

However, n slashes at the beginning or end of a format specification result
in n skipped or blank records. This is because the opening and closing
parentheses of the format specification are themselves a record initiator
and terminator, respectively; for example:
99

WRITE (6. 99)
FORMAT ('1' ,T51, 'HEADING LINE'//T51 , 'SUBHEADING LINE'//)

The previous statements produce the following output:
Column 50,

top of page

+
HEADING LINE

(blank line)
SUBHEADING LINE

(blank line)
(blank line)

8.6

External Field Separators
A field descriptor such as Fw.d specifies that an input statement is to read
w characters from the external record. If the data field in the external
record contains fewer than w characters, the input statement reads characters from the next data field in the external record, unless the short field is
padded with leading zeros or spaces.
When the field descriptor is numeric, you can avoid padding the input
field by using a comma to terminate the field . The comma overrides
the field descriptor's field width specification. This is called short field
termination. It is particularly useful when you are entering data from a
terminal keyboard. You can use it with the I, 0 , Z, F, E, D, G, and L field
descriptors; for example:
100

READ (5 ,100 ) I,J,A,B
FORMAT (2I6,2F10.2)

If the preceding statements read the following record :
1.-2.1.0,35

Based on this input, the following assignments occur:
I= 1

8-40 1/0 Formatting

J = -2
A= 1.0
B = 0.35

The physical end of the record also serves as a field terminator. The d
part of a w.d specification is not affected by an external field separator.
A comma can only terminate fields less than w characters long. If a
comma follows a field of w or more characters, the comma is considered
part of the next field.
Two successive commas or a comma after a field of w characters constitutes a null (zero-length) field. Depending on the field descriptor specified,
the resulting value assigned is 0, 0.0, O.DO, O.QO, or .FALSE.
A comma cannot terminate a field that is controlled by an A, H, or
character constant field descriptor. However, if the record reaches its
physical end before w characters are read, short field termination occurs
and the characters that were read are assigned successfully. Trailing
spaces are appended to fill the corresponding I/O list element or the field
descriptor.

8. 7 Run-Time Format
You can store format specifications in character scalar references, numeric array references, or numeric scalar field references (see Section
2.2.5.1). Such a format specification is called a run-time format and can be
constructed or altered during program execution.
A run-time format in an array has the same form as a FORMAT statement,
without the word FORMAT and the statement label. Opening and closing
parentheses are required. Variable format expressions are not permitted in
run-time formats.
Example

In the following example, the DATA statement assigns a left parenthesis to
the character array element FORCHR(O) and a right parenthesis and three
field descriptors to four character variables for later use.
Next, the proper field descriptors are selected for inclusion in the format
specification. The selection is based on the magnitude of the individual
elements of the array TABLE.
1/0 Formatting

8-41

A right parenthesis is then added to the format specification just before
the WRITE statement uses it. Thus, the format specification changes with
each iteration of the DO loop.
SUBROUTI NE PRI NT(TABLE)
REAL TABLE(10 ,5)
CHARACTER*5 FORCHR(0 :5) , RPAR*1 . FBIG, FMED , FSML
DATA FORCHR(O) ,RPAR /' (' . ') ' /
DATA FBIG.FMED .FSML /'F8 . 2. 'F9.4 , 'F9 .6 , '/
DO 20 I=1.10
DO 18 J=1,5
IF (TABLE(I,J) .GE. 100 . ) THEN
FORCHR(J) = FBIG
ELSE IF (TABLE(I , J ) .GT . 0 . 1) THEN
FORCHR(J) = FMED
ELSE
FORCHR(J) = FSML
END IF
CONTI NUE
FORCHR(5)(5 :5) = RPAR
WRITE (6 , FORCHR) (TABLE ( I , J) . J=1 ,5)
CONTINUE
END
I.

18
20

NOTE
Format specifications stored in arrays are recompiled at run time
each time they are used. If a Hollerith or character run -time
format is used in a READ statement to read data into the format
itself, that data is not copied back into the original array. Thus,
it will be subsequently unavailable for using that array as a
run-time format specification .

8.8

Format Control Interaction with 1/0 Lists
Format control begins with the execution of a formatted 1/0 statement.
The action taken by format control depends on information provided
jointly by the next element of the 1/0 list (if one exists) and the next field
descriptor of the format specification. Both the 1/0 list and the format
specification are interpreted from left to right, except when repeat counts
and implied-DO lists are specified.
If the 1/0 statement contains an 1/0 list, you must specify at least one I,
0, Z, F, E, D, G, L, A, or Q field descriptor in the format specification. An
error occurs if a field descriptor is not specified in this case.

8-42 1/0 Formatting

On execution, a formatted input statement reads one record from the
specified unit and initiates format control. Thereafter, additional records
are read as indicated by the format specification. Format control requires
that a new record be read when a slash occurs in the format specification,
or when the last closing parenthesis of the format specification is reached
and I/O list elements remain to be filled. Any remaining characters in the
current record are discarded when the new record is read.
On execution, a formatted output statement transmits a record to the
specified unit as format control terminates. Records can also be written
during format control if a slash appears in the format specification or if the
last closing parenthesis is reached and more I/O list elements remain to
be transferred.
The I, 0, Z, F, E, D, G, L, A, and Q field descriptors each correspond to
one element in the I/O list. No list element corresponds to an H, X, P,
T, TL, TR, SP, SS, S, BN, BZ, $, :, or character constant field descriptor.
In H and character constant field descriptors, data transfer occurs directly
between the external record and the format specification.
When an I/O list element is to be transferred, format field descriptors are
processed, beginning with the current format item, until a descriptor is
found that corresponds to an I/O list element. The I/O list element is
then transferred under control of the field descriptor.
Format execution continues until one of the following is encountered: an
element-transferring field descriptor, a colon edit descriptor, or the end
of the format. These also terminate format execution when no I/O list
elements are to be transferred.
When the last closing parenthesis of the format specification is reached,
format control determines whether more I/O list elements are to be
processed. If not, format control terminates. However, if additional list
elements remain, part or all of the format specification is reused in a
process called format reversion.
In format reversion, the current record is terminated, a new one is initiated, and format control reverts to the group repeat specification whose
opening parenthesis matches the next-to-last closing parenthesis of the
format specification. If the format does not contain a group repeat specification, format control returns to the initial opening parenthesis of the
format specification. Format control continues from that point.

1/0 Formatting 8-43

Example

The following annotated example shows several interactions between the
I/O list and the FORMAT statement.
Consider a data file named FOR002.DAT:
$ TYPE FOR002 . DAT
001 0101 0102 0103 0104 0105
002 0201 0202 0203 0204 0205
003 0301 0302 0303 0304 0305
004 0401 0402 0403 0404 0405
005 0501 0502 0503 0504 0505
006 0601 0602 0603 0604 0605
007 0701 0702 0703 0704 0705
008 0801 0802 0803 0804 0805
009 0901 0902 0903 0904 0905
010 1001 1002 1003 1004 1005
$

Assume that the data is to be processed 2 records at a time. Each record
starts with a number to be put into an element of a vector B, followed by
5 numbers to be put in a row in matrix A.
The following program uses several different FORMAT statements to read
the data in FOR002.DAT:
INTEGER I, J, A(2,5) , B(2)
100
999

200

READ (2,100) (B(I), (A(I,J), J=1,5) ,I=1,2) 0
FORMAT (2 (I3, X, 5(I4,X), /) ) f)
WRITE (6,999) B, ((A0,J) ,J=1,5) ,I=1,2) 8
FORMAT(' Bis', 203, X), '; A is', I
1
(I I . 5 04. X)) )
READ (2,200) (B(I), (A(I,J), J=1,5),I=1,2) ~
FORMAT (2 03, X, 504,X), : /))
WRITE (6. 999) B, ((AO, J), J=1, 5) , !=1, 2)

300

READ (2,300) (BO), (A(I,J), J=1,5) ,I=1,2) Ci)
FORMAT ( (I3, X, 5(14,X)) )
WRITE (6,999) B, ((A(I,J),J=1,5),I=1,2)

400

READ (2,400) (B(I), (A(I,J), J=1,5) ,I=1,2) 6)
FORMAT ( I3, X, 5(I4,X) )
WRITE (6,999) B, ((A0,J) ,J=1,5) ,!=1,2)
END

8-44 1/0 Formatting

Notes:

This starts by reading B(l); then A(l ,1) through A(l,5); then B(2) and
A(2,1) through A(2,5).
The first record (starting with 001) is read to start the processing of the
1/0 list.
There are two records, each in the format 13, X, 5(14, X). The / forces
the reading of the second record after A(l,5) is processed; it also forces
the reading of the third record after A(2,5) is processed-no data is
taken from that record.
This will output:
B is

2 ;

A is

101
201

102
202

103
203

104
204

105
205

This starts by reading the record starting with 004. The / forces the
reading of the next record after A(l,5) is processed; the : stops the
reading after A(2,5) is processed but before the / forces another read.

This will output:
B is

5 ;

A is

401
501

402
502

403
503

404
504

405
505

This starts by reading the record starting with 006. After A(l,5) is
processed, format reversion reads the next record and starts format
processing at the ( before the 13.

This will output:
B is

7 ;

601
701

602
702

603
703

A is
604 605
704 705

This starts by reading the record starting with 008. After A(l,5) is
processed, format reversion reads the next record and starts format
processing at the ( before the 14.

This will output:
B is
8 90 ; A is
801 802 803 804 805
9010 9020 9030 9040 100

1/0 Formatting

8-45

The record 009 0901 0902 0903 0904 0905 was processed with 14
as 009 for B(2), which is 90; X skips the next 0 then 901
is processed for A(2,1), which is 9010; 902 for A(2,2); 903
for A(2,3); and 904 for A(2,4). The repetition factor of 5 is now
exhausted and the format ends. Format reversion reads another record
and starts format processing at the ( before the 14 so that 010 is read
for A(2,5), which is 100.
11

;

8-46 1/0 Formatting

Chapter 9

Auxiliary 1/0 Statements
The following auxiliary IjO statements manage files during I/O operations:
•
•
•
•
•
•

•
•

OPEN-connects a FORTRAN logical unit to a file or device; declares
required attributes for read and write operations (see Section 9 .1 ).
CLOSE-terminates the connection between a logical unit and a file
or device (see Section 9.2).
INQUIRE-questions the status of specified properties of a file or
logical unit (see Section 9.3).
REWIND-repositions an open file to the beginning of that file (see
Section 9.4).
BACKSPACE-repositions an open file to the beginning of the preceding record in that file (see Section 9.5).
ENDFILE-writes an end-of-file record to a specified unit. When an
input statement reads this record, an end-of-file condition results (see
Section 9.6).
DELETE-deletes a record from a file (see Section 9.7).
UNLOCK- permits other programs to access a file that is locked by a
previous READ statement (see Section 9.8).

Auxiliary 1/0 Statements

9-1

9. 1 OPEN Statement
The OPEN statement connects an existing file to a logical unit or creates
a new file and connects it to a logical unit. In addition, it can specify file
attributes that control file creation and subsequent processing. The OPEN
statement takes the following form:
OPEN (par[ . par] .. . )

par
Is a keyword specification taking one of the following forms:
keywd
keywd = value

keywd
Is a keyword, as described in the text that follows (see also Table 9-1).
value
Depends on the keyword (see Table 9-1).

Keywords can be divided into several categories based on function:
•

•

9-2

Identifying the unit and file:
UNIT

- logical unit number to be used

FILE or NAME

- file-name specification for the file

DEFAULTFILE

- defa ul t fil e-na m e speci fi cation for th e fil e

STATUS or TYPE

- file existence status at OPEN

DISPOSE

- fil e existence s tatu s a ft er CLO SE

Describing file processing:
ACCESS

- FORTRAN access method to be used

ORGAN IZATION

- logical fil e stru cture

READONLY

- write protection

Auxiliary 1/0 Statements

•

Describing the records in a file:
BLOCKSlZE

- physical block size

CARRIAGECONT ROL

- printer control type

FORM

- type of FORTRAN record formatting

RECL or RECORDSIZE

- logical record length

RECORDTYPE

- logical record format

BLANK

- blank interpretation for numeric input

KEY

- positions of key fields within records in an
indexed fil e

Describing file storage allocation when a file is created:
INITIALSIZE

- initial file allocation

EXTENDSIZE

- file allocation increment size

Providing additional capability for direct access 1/0:
ASSOCIATEVARIABLE

- the next record number value

MAXREC

- maximum direct access record number

Providing improved performance or special capabilities; (these optional
keywords are generally transparent to 1/0 processing):
BUFFERCOUNT

- number of I/O buffers to be used

NOSPANBLOCKS

- records are not to be split across physical blocks

USEROPEN

- user program option to provide additional OPEN
capability

SHAR ED

- oth er programs can simultaneously access the
file

ERR

- statement to which control is transferred if
an error occurs during execution of the OPEN
statement

IOSTAT

- status value that indicates whether an error
condition exists

Table 9-1 lists the values accepted for each keyword.

Auxiliary 1/0 Statements

9-3

Table 9-1:

OPEN Statement Keyword Values

Keyword

Values

Function

Default

ACCESS

'SEQUENTIAL'
'DIRECT'
'KEYED'
'APPEND'

Access mode

'SEQUENTIAL'

ASSOCIATEVARIABLE

asv

Next direct access
record

BLANK

'NULL'
'ZERO'

Interpretation of
blanks

'NULL'

BLOCKSIZE

Physical block size

System default

BUFFERCOUNT

Number of I/O
buffers

System default

'FORTRAN'
LIST'
'NONE'

Print control

'FORTRAN'
(formatted)
'NONE'
(unformatted)

CARRIAGECONTROL

DEF A UL TFILE

Default file specificati on

DISPOSE
DISP

'KEEP' or 'SAVE'
'DELETE'
'PRINT'
'PRINT /DELETE'
'SUBMIT'
'SUBMIT / DELETE'

File disposition at
close

ERR

Error transfer label

'KEEP'

Key to Values
asv-an integer variable
v-an integer scalar memory reference
e-a numeric expression
s-a statement label
dt-a data type, INTEGER or CHARACTER
dr-direction, ASCENDING or DESCENDING
c-a character scalar reference, numeric scalar memory reference, or numeric array name reference
cl -a character expression
e 1-the first byte position of a key
e2-last byte position of a key
p-an external function

9-4

Auxiliary 1/0 Statements

Table 9-1 (Cont.):

OPEN Statement Keyword Values

Keyword

Values

Function

Default

EXTENDSIZE

File allocation increment

Volume or system
default

FILE
NAME

File-name specificati on

FORM

'FORMATTED'
'UNFORMATTED'

Format type

INITIALSIZE

File allocation

IOS TAT

l/O status

KEY

(e 1 :e2[:dt[ :dr]], .. .)

Key field definitions

MAXREC

Direct access record
limit

NOSPANBLOCKS
ORGANIZATION

CHARACTER
ASCENDING

Records do not span
blocks
'SEQUENTIAL'
' RELATIVE'
'INDEXED'

READONLY
RECL
RECORDSIZE

Depends on
ACCESS keyword

File structure

'SEQUENTIAL'

Write protection

Record length

Depends on record
type and file organization

Key to Values
asv-an integer variable
v-an integer scalar memory reference
e-a numeric expression
s-a statement label
dt- a data type, INTEGER or CHARACTER
dr-direction, ASCENDING or DESCENDING
c-a character scalar reference, numeric scalar memory reference, or numeric array name re feren ce
cl -a character expression
e1-the fi rst byte position of a key
e2- last byte position of a key
p-an external function

Auxiliary 1/0 Statements 9-5

Table 9-1 (Cont.):

OPEN Statement Keyword Values

Keyword

Values

Function

Default

REC ORDTYPE

'FIXED'
'VARIABLE '
'SEGMENTED '
'STREAM'
'STREAM_CR'
'STREAM_LF'

Record structure

Depends on
ORGANIZATION,
ACCESS, and
FORM keywords

File sharing allowed

SHARED
STATUS
TYPE

'OLD'
'NEW'
'SCRATCH'
'UNKNOWN'

File status at open

UNIT

Logical unit number

USE RO PE N

User program option

'UNKNOWN'

Key to Values
asv-an integer variable
v-an integer scalar memory reference
e-a numeric expression
s-a statement label
dt- a da ta type, INTEGER or CHARACTER
dr- direction, ASC ENDING or DESCENDING
c- a character scalar reference, numeric scalar memory reference, or numeric array name reference
cl-a character expression
e l - the fi rst byte position of a key
e2- last byte position of a key
p-an external function

Specifying OPEN Statement Keywords

Keyword specifications can appear in any order. In most cases, they are
optional. Default values apply in their absence. If the logical unit specifier
is the first parameter in the list, the UNIT keyword is optional.
You can specify character values at run time by substituting a general
character expression for a keyword value in the OPEN statement. The
character value can contain trailing spaces but not leading or embedded
spaces; for example:

9-6

Auxiliary 1/0 Statements

CHARACTER*7 QUAL /' '/

IF (exp) QUAL = '/DELETE'
OPEN (UNIT=l, STATUS='NEW'. DISP='SUBMIT'//QUAL)

Examples

The first statement creates a new sequential formatted file on unit 1 with
the default file name FOROOl.DAT.
OPEN (UNIT=l, STATUS='NEW', ERR=100)

The next statement creates a SO-block direct access file for temporary
storage. The file is deleted at program termination.
OPEN (UNIT=3, STATUS='SCRATCH', ACCESS='DIRECT' ,
1
I NITIALS IZE=50, RECL=64)

The next statement creates a file on magnetic tape with a large block size
for efficient processing.
OPEN (UNIT=!, FILE='MTAO :MYDATA .DAT', BLOCKSIZE=8192,
1
STATUS='NEW', ERR=14 , RECL=1024,
1
RECORDTYPE= 'FIXED 1 )

The next statement opens the file created in the previous example for
input.
OPEN (UNIT=!, FILE='MTAO :MYDATA .DAT' , READO NLY ,
1
STATUS='OLD' . RECL=1024 , RECORDTYPE='FIXED ',
1
BLOCKSI ZE= 8 1 9 ~

The next statement uses the file name supplied by the user and the default
file specification supplied by the DEFAULTFILE keyword to define the file
specification for an existing file.
TYPE * · 'ENTER NAME OF DOCUMENT'
ACCEPT * · DOC
OPEN (UNIT=l, FILE=DOC , DEFAULTFILE=' [ARCHIVE] .TXT',
1
STATUS='OLD')

The following sections provide specific information about OPEN statement
keywords. As used in these sections, a numeric expression can be any
integer or real expression. The value of the expression is converted to
integer data type before it is used in the OPEN statement.

Auxiliary 1/0 Statements 9-7

9.1.1

ACCESS Keyword
The ACCESS parameter specifies whether a file opens for keyed, direct, or
sequential access. It takes the following form:
ACCESS = ace

ace
Is a character expression having one of the following values:

•
•
•

'DIRECT'-by record number
'SEQUENTIAL'-by sequential access
'KEYED'- by a specified key

•

'APPEND'-sequentially, after the last record of the fil e

The default is 'SEQUENTIAL'.

9.1.2

ASSOCIATEVARIABLE Keyword
The ASSOCIATEVARIABLE parameter specifies the integer variable that
updates after each direct access I/O operation to reflect the record number
of the next sequential record in the file. This specifier is valid only for
direct access and is ignored for other access modes. It takes the following
form:
ASSOCI ATEVARIABLE = as v

asv
Is an integer variable. It cannot be a dummy argument to the routine in
which the OPEN statement appears.

9.1.3

BLANK Keyword
The BLANK parameter specifies how empty spaces are treated in a file. It
takes the following form:
BLANK = blnk

9-8

Auxiliary 1/0 Statements

blnk
Is a character expression with one of the following values:

•

'NULL'- ignore all blanks in a numeric field (except if the field is all
blank, in which case blanks are treated as zero)

•

'ZERO'-treat all blanks other than leading blanks as zeros

The default value is 'NULL'. Howeve r, if the /NOF77 qualifier is specified
on the FORTRAN command line, the defa ult is 'ZERO'.

9.1.4

BLOCKSIZE Keyword
The BLOCKSIZE param eter specifies the physical I/O transfer size for the
file. It takes the foll owing form :
BLOCKSI ZE = bks

bks
Is a numeric expression .

For magnetic tape files, the value of bks specifies the physical record size
in the range 18 to 32767 bytes . The default value is 2048 bytes.
For sequential disk files, the value of bks is rounded up to an integral
number of 512-byte blocks and used to specify multiblock transfers. The
number of blocks transferred can be 1 to 127. The number of blocks
transferred is determined by RMS defaul ts. Refer to the description of
the SET RMS_DEFAULT command in the VMS DCL Dictionary for more
information on setting process and system default multiblock counts if you
do not specify a block size.
For relative and indexed files, the value of bks is rounded up to an integral
number of 512-byte blocks and used to specify the RMS bucket size in the
range 1 to 63 blocks. The default is the smallest value capable of holding
a single record.

9.1.5

BUFFERCOUNT Keyword
The BUFFERCOUNT parameter specifi es the number of buffers to be associated wi th the logical unit for multibuffered 1/0. It takes the following
form :
BUFFERCOUNT = be

Auxiliary 1/0 Statements

9-9

be
Is a numeric expression.

The range of values for be is from 1 to 127. The size of each buffer is
determined by the BLOCKSIZE keyword . Thus, if BUFFERCOUNT=3
and BLOCKSIZE=2048, the total number of bytes allocated for buffers is
3*204 8, or 6144.
The BLOCKSIZE keyword determines the size of each buffer. If you do
not specify BUFFERCOUNT, or if you specify zero, the system default is
assumed. Refer to the description of the SET RMS_DEFAULT command
in the VMS DCL Dictionary for information on setting process and system
default buffer counts.

9.1.6

CARRIAGECONTROL Keyword
The CARRIAGECONTROL parameter determines the type of carriage
control processing used when printing a file. It takes the following form :
CARRIAGECONTROL = cc

cc
Is a character expression taking one of the following values:

•
•
•

'FORTRAN'-norm al FO RTRAN interpretation of the first character
'LIST'-single spacing between records
'NONE '-no implied carriage control

The default for forma tted files is 'FORTRAN'; for unformatted files, the
default is 'NONE'.

9.1.7

DEFAULTFILE Keyword
The DEFAULTFILE parameter specifies a default file specification string. It
takes the following fo rm :
DEFAULTF ILE = ce

9-10

Auxiliary 1/0 Statements

ce
ls a character expression that contains a default fil e name specification
string.
This keyword can supply a value to the RMS default file specification
string for the missing components of a file specification. If you do not
specify the DEFAUL TFILE keyword, FORTRAN uses the default value
'FORnnn.DAT', where nnn is the unit number with leading zeros.
The default file specification string is used primarily when accepting file
specifications interactively. File specifications known to a user program
are normally completely specified in the FILE keyword.
You can specify default values for any one of the following filespecification components:

•
•
•
•
•
•

Node
Device
Directory
File name
File type
File version number

When you specify any of the above components in the FILE=keyword,
they override those values specified in the DEFAULTFILE=keyword. Refer
to the VMS Record Management Services Manual for more information.

9.1.8

DISPOSE Keyword
The DISPOSE (or DISP) parameter determines the disposition of the
file connected to a logical unit when the unit closes. It takes one of the
following forms:
DISPOSE = dis
DISP = dis

dis
Is a character expression having one of the following values:

•

'KEEP' or 'SAVE'-

retain the file after the unit closes

•

'DELETE'-delete the file after the unit closes

•

'PRINT'-submit the file to the system line printer spooler and
retain it
Auxiliary 1/0 Statements

9-11

•
•
•

'PRINT / DELETE'-submit the file to the system line printer spooler
and then delete it
'SUBMIT'-submit the file to the batch job queue and retain it
'SUBMIT / DELETE' -submit the file to the batch job queue and then
delete it

A read-only file cannot be deleted. A scratch file cannot be saved, printed,
or submitted.
The default is 'KEEP' or 'SAVE'.

9. 1.9

ERR Keyword
The ERR parameter identifies the executable statement that receives
control when an error occurs. It takes the following form:
ERR = s

s
Is the label of an executable statement.
The ERR parameter applies only to the OPEN statement in which it is
specified and not to subsequent 1/0 operations on the unit. If an error
occurs, no file is opened or created.

9. 1. 10

EXTENDSIZE Keyword
The EXTENDSIZE parameter specifies the number of blocks by which to
extend a disk file when additional storage space is allocated. It takes the
following form:
EXTENDSIZE = es

es
Is a numeric expression.
If you do not specify EXTENDSIZE or if you specify zero, the system

default for the device is used.
See Section 9.1.13 for a discussion about the relationship between the
EXTENDSIZE keyword and the INITIALSIZE keyword.

9-12

Auxiliary 1/0 Statements

9.1.11

FILE Keyword
The FILE parameter specifies the name of the file to be connected to the
unit. It takes the following form:
FILE = fln

fin
Is a character scalar reference, numeric scalar memory reference, or
numeric array name reference .

The name of a file can be any specification accepted by the operating
system. (See the VAX FORTRAN User Manual for a de~cription of default
file name conventions.)
If the file name is stored in a numeric scalar or array, the name must
consist of ASCII characters terminated by an ASCII null character (zero
byte). However, if it is stored in a character scalar or array, it must not
contain a zero byte.

9.1.12

FORM Keyword
The FORM parameter specifies whether the file being opened is read or
written using formatted or unformatted READ or WRITE statements. It
takes the following form:
FORM = ft

ft
Is a character expression taking one of the following values:
•
•

'FORMATTED'
'UNFORMATTED'

The default is 'FORMATTED' for sequential access files, and 'UNFORMATTED'
for direct and keyed access files.

Auxiliary 1/0 Statements

9-13

9.1 .13 INITIALSIZE Keyword
The INITIALSIZE parameter specifies the number of blocks in the initial
storage allocation for a disk file. It is contracted by the EXTENDSIZE
parameter, which specifies th e number of blocks by which a disk file is
extended each time more space is needed for a file . The INITIALSIZE
parameter takes the following form :
I NITIALSIZE = insz

insz

Is a numeric expression .
If you do not specify INITIALSIZE or if you specify zero, no initial
allocation is made. The system attempts to allocate contiguous space fo r
INITIALSIZE. If not enough contiguous space is available, noncontiguous
space is allocated.

INITIALSIZE is effective only at the time the file is created. If
EXTENDSIZE is specifi ed when the file is created, the value specified
is the default value used to allocate additional storage for the file . If
you specify EXTENDSIZE when you open an existing file, the value you
specify supersedes any EXTENDSIZE value specified when the file was
created, and remains in effect until you close the fil e. Unless specifically
overridden, the defa ult EXTENDSIZE value is in effect on subsequent
openings of the file.

9.1.14

IOSTAT Keyword
The IOSTAT parameter specifies 1/0 status. It takes the following form:
IOSTAT = ios
105

Is an integer scalar memory reference.
This parameter causes ios to be defined as follows:
•
•

9-14

Zero-if no error condition exists
A positive integer-if an error condition exists

Auxiliary 1/0 Statements

VAX FORTRAN I/O status values are described in the VAX FORTRAN
User Manual. IOSTAT applies only to the OPEN statement in which it
appears and not to subsequent I/O operations on the logical unit that is
opened. However, you can use the IOSTAT parameter in subsequent I/O
statements to perform a similar function (see Section 7.1.1.9).

9.1.15

KEY Keyword
The KEY parameter defines the access keys for records in an indexed file.
It takes the following form:
KEY = (kspe c[ ,k spec ] . . . )

ks pee

Takes the following form :
e 1 : e 2 [ : d t [ : dr ]]

Is the first byte position of the key.

e2
Is the last byte position of the key.

dt
Is the data type of the key: INTEGER or CHARACTER.

dr
Is the direction of the key: ASCENDING or DESCENDING.
CHARACTER and ASCENDING are the default values.
The key starts at position e 1 in a record and has a length of e2 - el + 1.
The values of el and e2 must be such that the following calculations are
true:
1 . LE . ( e1 ) . AND . ( e1 ) . LE . ( e2 )
1 . LE . ( e2 - e1+1 ) . AND . ( e2 - e1+1 )

. AND. (e2)
. LE . 255

. LE . record-length

If the key type is INTEGER, the key length must be either 2 or 4.

Auxiliary 1/0 Statements 9-15

Defining Primary and Alternate Keys

You must define at least one key in an indexed file . This primary key is
the default key. It usually has a unique value for each record .
You can choose to define alternate keys. RMS allows up to 254 alternate
keys . However, individual OPEN statements only allow up to 85 key definitions, a number that is fu rther reduced wh en multiple OPEN statements
appear together in a program unit.
If a file requires more keys than the OPEN statement limit, you must
create it from another language or with the File Definition Language
(FDL). For information on FDL, see the VMS Record Management Services

Manu al.
Specifying and Referencing Keys

You must specify the KEY parameter when creating an indexed file.
However, you do not have to respecify it when opening an existing file
because key attributes are permanent aspects of the file . These attributes
include key definitions and reference numbers for subsequent I/O operations. If you do choose to specify the KEY parameter for an existing file ,
your specification must be identical to the established key attributes.
Subsequent I/O operations use a reference number, called the key-ofreference number, to identify a particular key. You do not specify this
number; it is determined by the key's position in the specification list:
the primary key is key-of-reference number O; the first alternate key is
key-of-reference number 1, and so forth.

9.1.1 6 MAXREC Keyword
Th e MAXREC parameter applies only to direct access files . It specifies
the maximum number of records permitted in a direct access file . The
MAXREC parameter takes the following form:
MAXREC = mr

mr
Is a numeric expression.
The default is an unlimited number of records.

9-16 Auxiliary 1/0 Statements

9. 1. 17

NAME Keyword
NAME is a n onstandard synonym fo r FILE. See Section 9.1.11.

9.1 .18

NOSPANBLOCKS Keyword
The NOSPANBLOCKS parameter specifi es that records are not to cross
disk block boundaries. It takes the followin g form:
NOSPANBLOCKS

When you specify this parameter, an error occurs if any record exceeds the
size of a physical block.

9. 1. 19

ORGANIZATION Keyword
The ORGANIZATION parameter speci fies the internal organization of the
file. It takes the follo wing form :
ORGANIZATIO N = org

org
Is a character expression with one of the fo llowing values :

•

'SEQUENTIAL'

•

'RELATIVE'

•

'INDEXED'

The default file organization is sequential. However, if you omit the
ORGANIZATION keyword when you open an existing fil e, the organization already specified in that file is used. If you specify ORGAN IZATIO N
for an existing file, org must ha ve the sam e value as that of the existing
file.

Auxiliary 1/0 Statements

9-17

9.1.20

READONLY Keyword
The READONLY parameter specifies that an existing file can be read and
prohibits writing to that file. It takes the following form:
READONLY

The FORTRAN 1/0 system's default file access privileges are readwrite, which can cause run-time 1/0 errors if the file protection does
not permit write access. The READO NL Y keyword has no effect on the
protection specified for a file. Its main purpose is to allow a file to be read
simultaneously by two or more programs. For example, if you wish to
open a file for the purpose of reading the file but want to allow others
to read the same file while you have it open, specify the READO NLY
keyword. Refer to the VAX FORTRAN User Manual for information on file
sharing.

9. 1.21

RECL Keyword
The RECL parameter specifies the length of logical records in a file. It
takes the following form:
RECL = rl

rl
Is a numeric expression indicating the length of logical records in the file.
The value of rl does not include space for control information, such as for
two segment control bytes (if present) or the bytes that RMS requires for
maintaining record length and deleted record control information. The
specification is for record data only.
The value of rl is expressed in units of bytes or longwords, depending on
the record's format. Formatted records use byte units and unformatted
records use longword units (which are equal to 4 bytes). Table 9-2 lists
the maximum values that can be specified for rl, based on file organization
and record format.

9-18

Auxiliary 1/0 Statements

Table 9-2:

Record Size (RECL) Limits
Record Format

File Organization

Sequential

Formatted (bytes)

Unformatted
(longwords)

32766

8191

Sequential and variablelength records on ANSI
magnetic tape

9999

Relative and indexed

16380

2499 1

4095

Limit imposed by 4-byte ASCII count field .

RECL is mandatory when opening files with fixed-length records or
relative or indexed organization; it is optional when opening all other
types. Default values for optional cases depend on the value of the
RECORDTYPE parameter. Table 9-3 lists the RECL default values.
Table 9-3:

Record Size (RECL) Default Values

RECORDTYPE value

RECL value

'FIXED'

none; value must be explicitly specified

'SEGMENTED'

2048

All other types

133

The interpretation and effect of the logical record length varies as follows:
•

If the file contains fixed-len gth records, RECL specifies the size of each
record.

•

If the file contains variable-length records, REC L specifies the maximum length for any record.

•

If your program attempts to write to an existing file a record that is
longer than the logical record length, an error occurs.

•

If you are opening an existing file that contains fixed-length records or
that has relative organization and you specify a value for RECL that
is different from the actual length of the records in the file, an error
occurs.

Auxiliary 1/0 Statements

9-19

9. 1.22

RECORDSIZE Keyword
RECORDSIZE is a nonstandard synonym for RECL; refer to Section 9 .1.21
for more information.

9.1.23

RECORDTYPE Keyword
The RECORDTYPE parameter specifies whether the file has fixed-length
records, variable-length records, segmented records, or stream-type
variable-length records . It takes the following form:
RECORDTYPE = ty p

typ
Is a character expression with one of the following values:

•
•

'FIXED '

•

'SEGMENTED'

•
•
•

'STREAM'

'VARIABLE'

'STREAM_CR'
'STREAM_LF'

When you create a file, default record types are as follows:
File Type

Default Record Type

Relative or indexed files

'FIXED'

Direct access sequential files

'FIXED'

Formatted sequential access fil es

'VARIABLE'

Un form atted sequential access files

'SEGMENTED'

A segmented record consists of one or more variable-length records.
Using segmented records allows a FORTRAN logical record to span
several physical records. Only unformatted sequential access files with
sequential organization can use segmented records. You cannot specify
'SEGMENTED' for any other fi le type.

9-20

Auxiliary 1/0 Statements

If you do not specify the RECORDTYPE parameter when you are accessing an existing file, the record type of the file is used- except for
unformatted sequen tial-access files with sequential organization and
variable-length records. These files have a default of 'SEGMENTED'.
If you do specify the RECORDTYPE parameter when you are accessing an
existing file, the type that you specify must match the type of an existing
file.
In fixed-length record files, if an output sta tement does not specify a full
record, the record is filled with spaces in a formatted file and zeros in an
unforma tted file.
You cannot use an unformatted READ statement to access an unformatted
sequential organization file containing variable-length records, unless you
specify the corresponding RECORDTYPE value in your OPEN statement.
Files containing segmented records can be accessed only by unformatted
sequential FORTRAN I/ O statements.

9.1.24

SHARED Keyword
The SHARED parameter specifies that the file can be opened for shared
access by more than one program executing simultaneously. It takes the
fo llowing form :
SHARED

For information on file sharing, see the VAX FORTRAN User Manual.

9.1.25

STATUS Keyword
The STATUS parameter specifies the status of the file that you wish to
open. It takes the following form:
STATUS = sta

sta
Is a character expression with one of the following values:
•
•
•

'OLD'-the file must already exist.
'NEW'-a new file is created.
'SCRATCH'-a new file is created and is deleted when it closes.

Auxiliary 1/0 Statements

9-21

•

'UNKNOWN'-the processor first tries 'OLD'; if the file is not found,
the processor uses 'NEW', thereby creating a new file.

The default is 'UNKNOWN'. However, if you specify the / NOF77 qualifier on the FORTRAN command line, the default value specified by the
compiler is 'NEW'.
NOTE

The STATUS parameter is also used in CLOSE statements to
specify the status of a file after the file is closed. However,
the values it uses are different from those used in OPEN
statements.

9.1.26

TYPE Keyword
TYPE is a nonstandard synonym for STATUS. See Section 9.1.25 .

9. 1.27

UNIT Keyword
The UNIT parameter specifies the logical unit that connects to the file. It
takes the following form:
[UNIT=] u

u
Is a numeric expression.
The unit specification must appear in the parameter list unless the unit
specifier occupies the first position in the list.
The logical unit may already be connected to a file when an OPEN
statement is executed. If this file is not the same as the one to be opened,
the OPEN statement executes as if a CLOSE statement had executed just
before it. If the file to be opened is already connected to the unit, or if the
file specifier (FILE keyword) is not included in the OPEN statement, only
the blank specifier (BLANK keyword) can have a value different from the
one currently in effect. The position of the file is unaffected.
See the VAX FORTRAN User Manual for additional information about
logical unit numbers.

9-22

Auxiliary 1/0 Statements

9. 1.28

USEROPEN Keyword
The USEROPEN parameter specifies a user-written externa l functio n that
controls the opening of the fil e. It takes the foll owing fo rm:
USEROPEN = proce dur e-name

procedure-name
ls the symbolic name of the USEROPE N procedure.

The procedure name must be declared EXTERNAL.
Knowledgeable users can employ additional features of the operating
system that are not directly available from FORTRAN, while retaining the
convenience of writing programs in FORTRAN. See the VA X FORTRA N
Us er Manual for more information on USEROPEN .

9.2 CLOSE Statement
The CLOSE statement disconnects a file from a unit. It takes the following
form:
CLOSE ([UNIT=] u [,

STATUS
DISPOSE
DISP

=p] [, ERR=s] [ , IOSTAT=ios])

u
Is a logical unit number.
p
Is a character expression that determines the disposition of the file. It can
be any one of the following values:

•

'SAVE' or 'KEEP'- retain the file after the unit closes

•
•
•

'DELETE' - delete the file
'PRINT '- submit the fil e to the line printer spooler and retain it
'PRINT / DELETE '- submit the fil e to th e line printer spooler and then
delete it
'SUBMIT'- submit the file to the batch job queue and retain it

•
•

'SUBMIT /DELETE '-submit th e fil e to the batch job queue and then
delete it

Auxiliary 1/0 Statements

9-23

The default is 'DELETE' for scratch files. For all other files, the default
is 'KEEP'.

s
Is the label of an executable statement.
ios

Is an integer scalar memory reference.
Syntax Rules and Behavior
CLOSE statement parameters can occur in any order. The UNIT keyword
is optional only if the unit specifier is the first parameter in the list.
The disposition specified in a CLOSE statement supersedes the disposition
specified in the OPEN statement, except that a file opened as a scratch file
cannot be saved, printed, or submitted, and a file opened for read-only
access cannot be deleted . For example, the following statement closes the
file on unit 1 and submits it for printing:
CLOSE (UNIT=1, STATUS= ' PRI NT' )

The next statement closes the file on unit J and deletes it:
CLOSE (UNIT=J , STATUS='DELETE' , ERR=99)

9.3 INQUIRE Statement
The INQUIRE statement "asks" about specified properties of a file or of a
logical unit on which a file might be opened. It takes two forms, one for
inquiring by file and the other for inquiring by unit:

Inquiring by File
I NQUIRE (FILE=fi [ ,DEFAULTFILE=dfi .. . ] ,flist)

Inquiring by Unit
I NQUIRE ([UNIT=]u ,flist)

9-24 Auxiliary 1/0 Statements

fi
Is a character expression, numeric scalar memory reference, or numeric
arra y name reference whose value specifies the name of the file to be
inquired about.
dfi
Is a character expression specifying a default file name specification string.
flist
Is a list of property specifiers in which any one specifier appears only
once. The specifiers are described in the following sections.
u
Is the number of the logical unit to be inquired about. The unit does not
have to exist, nor does it need to be connected to a file. If the unit is
connected to a file, the inquiry encompasses both the connection and the
file.

Syntax Rules and Behavior
FILE=fi and UNIT=u can appear anywhere in the property-specifier list;
however, if the UNIT keyword is omitted, the unit specifier (u) must be
the first parameter in the list.
DEFAUL TFILE=dfi can be used in addition to or in place of FILE=fi wh en
used in connection with an inquiry about a file. If a file is open with
both FILE and DEFAULTFILE keywords specified in the OPEN statement,
then you can inquire about this file by specifying both the FILE and
DEFAULTFILE keywords in the INQUIRE statement.
An INQUIRE statement may be executed before, during, or after the
connection of a file to a unit. The values assigned by the statement are
those that are current when the INQUIRE statement executes.

9.3.1

ACCESS Specifier
The ACCESS specifier takes the following form:
ACCESS = ace

Auxiliary 1/0 Statements 9-25

ace
Is a character scalar memory reference that is assigned one of the following
values:

9.3.2

•

SEQUENTIAL-if the file is open for sequential access

•

DIRECT-if the file is open for direct access

•
•

KEYED-if the file is open for keyed access
UNKNOWN-if no connection exists

BLANK Specifier
The BLANK specifier takes the following form:
BLANK = blk

blk
Is a character scalar memory reference that is assigned one of the following
values:

•
•
•

9.3.3

NULL-if null blank control is in effect for a file open for formatted
I/O
ZERO-if zero blank control is in effect
UNKNOWN-if no connection exists or if the connection is not for
formatted 1/ 0

CARRIAGECONTROL Specifier
The CARRIAGECONTROL specifier takes the follo wing form :
CARR I AGECO NTROL = cc

cc
Is a character scalar memory reference that is assigned one of the foll owin g
values:

•
•
•
•

S-26

FORTRAN-if the file has FORTRAN carriage control
LIST-if the file has implied carriage control
NONE-if the file has no carriage control attribute
UNKNOWN-if no other values apply

Auxiliary 1/0 Statements

9.3.4

DIRECT Specifier
The DIRECT specifier takes the following form :
DIRECT = dir

dir
Is a character scalar memory reference that is assigned one of the following
values:

9.3.5

•

YES-if direct access is allowed for the file

•

NO-if direct access is not allowed

•

UNKNOWN-if the processor cannot determine whether direct access
is allowed

ERR Specifier
The ERR specifier takes the following form:
ERR = s

s
Is the label of an executable statement.
The ERR specifier is a control specifier rather than a property specifier.
If an error occurs during execution of the INQUIRE statement, control is
transferred to the statement whose label is s.

9.3.&

EXIST Specifier
The EXIST specifier takes the following form:
EXIST = ex

ex
Is a logical scalar memory reference that is assigned one of the following
values:

•

.TRUE.-if the specified file or unit exists

•

.FALSE.-if the specified file or unit does not exist or the file cannot
be opened even though it exists

Auxiliary 1/0 Statements 9-27

9.3. 7 FORM Specifier
The FORM specifier takes the following form:
FORM = f m

fm
Is a character scalar memory reference that is assigned one of the following
values:

•
•
•

9.3.8

FORMATTED-if the file is open for formatted I/O
UNFORMATTED-if the file is open for unformatted I/O
UNKNOWN-if no connection exists

FORMATIED Specifier
The FORMATTED specifier takes the following form:
FORMATTED = fmd

fmd
Is a character scalar memory reference that is assigned one of the following
values:

•
•
•

9.3.9

YES-if formatted is an allowed form for the file
NO-if formatted is not an allowed form
UNKNOWN-if the processor is unable to determine whether formatted is an allowed form

IOSTAT Specifier
The IOSTAT specifier takes the following form:
IOSTAT = ios

9-28 Auxiliary 1/0 Statements

ios
Is an integer scalar memory reference.

The IOSTAT specifier is a control specifier rather than a property specifier.
Ios can be assigned one of the following values:

9.3. 10

•

If an error occurs during execution of the INQUIRE statement, it takes
a processor-dependent positive integer value.

•

If no error occurs, it takes a ZERO value.

KEYED Specifier
The KEYED specifier takes the fo llowing form :
KEYED = kyd

kyd
Is a character scalar memory reference that is assigned on e of the following
values:

9.3.11

•
•

YES- if keyed access is allowed for the file (The fil e must be indexed.)
NO-if keyed access is not allowed

•

UNKNOWN- if the processor is unable to determine whether keyed
access is allowed

NAME Specifier
The NAME specifier takes the following form:
NAME = rune

nme
Is a character scalar memory reference that is assigned the name of the file
being inquired about. If the file does not have a name, nme is undefined.
The value assigned to nme is not necessarily identical to the value specified with the FILE keyword. For example, the value that the processor
returns may be qualified by a directory name or a version number.
However, the value that is assigned is always valid with the FILE keyword
in an OPEN statement.

Auxiliary 1/0 Statements

9-29

NOTE
The FILE and NAME keywords are synonyms when used with
the OPEN statement, but not when used with the INQUIRE
statement.

9.3.12

NAMED Specifier
The NAMED specifier takes the following form:
NAMED = nmd

nmd
Is a logical scalar memory reference that is assigned one of the following
values:

•
•

9.3. 13

.TRUE.-if the specified file has a name
.FALSE.- if it does not have a name

NEXTREC Specifier
The NEXTREC specifier takes the following form:
NEXTREC = nr

nr
Is an integer scalar memory reference that is assigned one of the following
values:

9.3.14

•

If a record was previously read or written on the specified unit, the
value of nr is one more than the number of that record.

•

If no records have been read or written, the value of nr is one.

•

If the file is not opened for direct access or if the position is indeterminate because of an error condition, nr is zero .

NUMBER Specifier
The NUMBER specifier takes the following form:
NUMBER = num

9-30

Auxiliary 1/0 Statements

num
Is an integer scalar memory reference.

Num is assigned the number of the logical unit currently connected to the
specified file. If there is no logical unit connected to the file, num is not
defined.

9.3. 15

OPENED Specifier
The OPENED specifier takes the following form:
OPENED = od

od
Is a logical scalar memory reference that is assigned one of the following
values:
•
•

9.3.16

.TRUE.-if the specified file is open on a unit or if the specified unit is
open
.FALSE.-if the specified file or unit is not open

ORGANIZATION Specifier
The ORGANIZATION specifier takes the following form:
ORGANIZATIO N= org

org
Is a character scalar memory reference that is assigned one of the following
values:

•
•
•
•

SEQUENTIAL-if the file is a sequential file
RELATIVE-if the file is a relative file
INDEXED-if the file is an indexed file
UNKNOWN-if the processor is unable to determine the file 's
organization

Auxiliary 1/0 Statements

9-31

9.3. 17

RECL Specifier
The RECL specifier takes the following form:
RECL = rel

rel
Is an integer scalar memory reference taking one of the following values:

•

If the file or unit is open, rel is the maximum record length allowed in
the file.

•

If the file is not open, rel is the maximum record length allowed in
the file; or, if the maximum record length is 0, rel is the length of the
longest record in the file.
If inquiring about a file that has no maximum record size, see
Section 9.1.21.

•

If the file is segmented, rel is the longest segment length in the file.

•

If a specified file does not exist, rel is zero.

The rel value is expressed in longwords if a file is (or has been) opened for
unformatted I/O; and in bytes in all other circumstances.

9.3.18

RECORDTYPE Specifier
The RECORDTYPE specifier takes the follow ing fo rm :
RECORDTYPE = rtype

rtype
Is a character scalar memory reference that is assigned one of the fo llowing
values:

•
•
•

9- 32

FIXED- if the fil e is open for fixed-length records
VARIABLE- if the file has variable-length records
SEGMENTED- if the file is open fo r unformatted sequential I/O
using segmented records

•

STREAM- if the file 's records are terminated with a carriage-retu rn
and line-feed

•

STREAM _ CR- if the fi le's records are terminated only with a
carriage-return

Auxiliary 1/0 Statements

•
•

9.3. 19

STREAM_LF-if the file 's records are terminated only with line -feed
UNKNOWN-if the processor cannot determine the record type

SEQUENTIAL Specifier
The SEQUENTIAL specifier takes the following form:
SEQUENTIAL = seq

seq
Is a character scalar memory reference that is assigned one of the following
values:

9.3.20

•

YES-if sequential access is allowed for the specified file

•
•

NO-if sequential access is not allowed
UNKNOWN-if the processor cannot determine whether sequential
access is allowed

UNFORMATIED Specifier
The UNFORMATTED specifier takes the following form:
UNFORMATTED = unf

unf
Is a character scalar memory reference that is assigned one of the following
values:

•
•
•

YES-if unformatted is an allowed form for the file
NO-if unformatted is not an allowed form for the file
UNKNOWN-if the processor is unable to determine whether unformatted is an allowed form for the file

Auxiliary 1/0 Statements 9-33

9.4 REWIND Statement
The REWIND statement repositions a sequential file currently open for
sequential or append access to the beginning of the file . It takes either one
of the following forms:
REWIND ([UNIT=]u[,ERR=s] [,IOSTAT=ios])
REWIND u

u
Is a logical unit number.

s
Is the label of the executable statement that receives control if an error
occurs.
IDS

Is an integer scalar memory reference that is assigned a positive integer if
an error occurs and zero if no error occurs.
Syntax Rules and Behavior

The unit number must refer to a file on disk or magnetic tape. For example, the following statement repositions logical unit 3 to the beginning of
the currently open file:
REWIND 3

This statement repositions logical unit 3 to the beginning of the currently
open file .
A REWIND statement should not be issued for a file that is open for direct
or keyed access.

9-34 Auxiliary 1/0 Statements

9.5

BACKSPACE Statement
The BACKSPACE statement repositions a sequential file currentl y open for
sequential access to the beginning of the preceding record. When the next
I/O statement for the unit is executed, the preceding record is available for
processing. The BACKSPACE statement takes one of the following form s:
BACKSPACE ([UNIT=]u[,ERR=s] [ , IOSTAT=io s] )
BACKSPACE u

u
Is a logical unit number.

s
Is the label of the executable statement that receives control if an error
occurs.
ios
Is an integer scalar memory reference that is defined as a positive integer
if an error occurs and zero if no error occurs.

Syntax Rules and Behavior

The unit number must refer to an open file on disk or magnetic tape . For
example, the following statement repositions the open file on logical
unit 4 to the beginning of the preceding record:
BACKSPACE 4

A BACKSPACE statement should not be issued for a file that is open for
direct, keyed, or append access. Backspacing from record n is done by
rewinding to the start of the file and then performing n-1 successive reads
to reach the previous record. For direct, keyed, and append access, the
current record count (n) is not available to the FORTRAN I/O system.

9.6

ENDFILE Statement
The ENDFILE statement writes an end-file record to the specified unit. It
takes one of the following forms:
ENDFILE ([UNIT=]u[ , ERR=s ] [ , IOSTAT=ios ])
ENDFILE u

Auxiliary 1/ 0 Statements

9-35

u
Is a logical unit number.

s
Is the label of the executable statement that receives control if an error
occurs.
ios

Is an integer scalar memory reference that is defined as a positive integer
if an error occurs and zero if no error occurs.
Syntax Rules and Behavior
If the unit specified in the ENDFILE statement is not open, the default file
is opened for unformatted output.

An end-file record can be written only to files with sequential organization
that are accessed as formatted -sequential or unformatted-segmented
sequential files. For example, the following statement writes an end-file
record to the logical unit 2:
ENDFILE 2

An ENDFILE statement must not be issued for a file that is open for direct
or keyed access.
End-file records should not be written in files that are read by programs
written in a language other than FORTRAN because VAX RMS does not
support the embedded end-file concept. An end-file record is a 1-byte
record containing the hexadecimal code lA (CTRL/Z).

9. 7 DELETE Statement
The DELETE statement deletes records from relative and indexed files. It
takes one of the following forms :
Indexed File Access
DELETE ([UNIT=] u [ . ERR=s] [. IOSTAT=ios])

Relative File Access
DELETE ([UNIT=]u,REC=r[,ERR=s] [ ,I OSTAT=ios])
DELETE (u' r[ ,ERR=s] [,IOSTAT=ios])

9-36 Auxiliary 1/0 Statements

u
Is the number of the logical unit containing the record to be deleted.

r
Is the positional number of the record to be deleted .

s
Is the label of an executable statement that receives control if an error
condition occurs.
I DS

Is an integer scalar memory reference that is defined as a positive integer
if an error occurs and zero if no error occurs.
Syntax Rules and Behavior

The form of the DELETE statement fo r indexed files is a current-record
delete . This form deletes the curren t record, which is the last record that
is accessed by a READ statement on th e specified logical unit.
The forms of the DELETE statemen t with relative files are direct access
deletes. These forms delete the record specified by the number r.
The DELETE statement logicall y removes the appropriate record from the
specified file by locating the record and marking it as a deleted record . It
then frees the position fo rmerly occupied by the deleted record so that a
new record can be written into that position.
Following a direct access delete, any associated variable is set to the next
record number.
In the following example, the fi fth record in the file connected to logical
unit 10 is deleted from the file:
DELETE (10 , REC =5)

In the next example, the current record is deleted from the file connected
to logical unit 11:
DELETE (1 1)

Auxiliary 1/0 Statements

9-37

9.8 UNLOCK Statement
The UNLOCK statement frees a record in an indexed, relative, or sequential file that was locked on a specified logical unit by a previous READ. It
perform s no other I/O operation. The UNLOCK statement takes one of
the following form s:
UNLOCK ([UNIT=] u [ , ERR=s ] [ , IOSTAT=ios])
UNLOCK u

u
Is the number of a logical unit.

s
Is the label of the executable statement that receives control if an error
occurs .
ios

Is an integer scalar memory reference that is defined as a positive integer
if an error occurs and zero if no error occurs.
If no record is locked, the operation has no effect.

9-38

Auxiliary 1/0 Statements

Chapter 10

Compiler Directives
Compiler directives tell the compiler to perform certain tasks when it
compiles a source program unit. They are preceded by special tags that
identify them to the compiler.
VAX FORTRAN provides two categories of compiler directives: one
category, parallel directives, supports directed decomposition for parallel
processing. Parallel directives are preceded by the CP AR$ tag. The other
category, general directives, provides several general -purpose functions.
General directives are preceded by the CDEC$ tag.

10. 1 Compiler Directive Syntax Rules
The follow ing general syntax rules appl y to all compiler directives. They
must be precisely follo wed to properly compile your program and obtain
meaningful results:
•
•

The tag (CPAR$ or CDEC$) must appear in columns 1 through 5.
Column 6 must be a blank or tab.

•

From column 7 on, blanks are insignificant. Thus, the directive can be
positioned anywhere on the line after column 6.

•
•

Continuation lines cannot appear in compiler directives.
If a blank common block is used in a compiler directive, it must be
specified as two slashes (/ /) .

See the individual sections in this chapter for listings of rules that pertain
only to specific categories or individual directi ves.

Compiler Directives

10-1

10.2 Parallel Directives
Parallel directives invoke parallel processing of indexed DO-loops, syn chronize execution of critical regions within the loops, and define the
sharability of common blocks and symbols in parallel applications.
Th e /PARALLEL qualifier enables parallel directives. See the VAX
FORTRAN User Manual for details about this qualifier.
Parallel directives take the follow ing form :
col umn 1

CPAR$ di rective

directive
Is any one of the following values:
•
•
•
•
•
•
•
•

CONTEXT_ SHARED-specifies shared memory locations for symbols
declared in routines that con tain parallel DO-loops.
CONTEXT_SHARED_ALL-reinforces the context-shared default of
symbols in routines compiled with the /PARALLEL qualifier.
DO_ PARALLEL- enables parallel processing of indexed DO-loops.
LOCKON and LOCKOFF- forces processes to sequentially execute a
region of code.
SHARED-specifies shared common blocks for parallel processing.
SHARED_ALL-reinforces the shared default of common blocks in
routines compiled with the / PARALLEL qualifier.
PRIVATE-specifies unique (private) common blocks or symbols for
each process.
PRIVATE_ALL-forces all common blocks and symbols to have
PRIVATE defaults in routines compiled with the /PARALLEL qualifier.

Section 10.2.9 provides examples of parallel directives appropriately used
in a program unit.

10-2 Compiler Directives

10.2.1

CPARS CONTEXT_SHARED
The CONTEXT_SHARED directive specifies that the same memory
location will be used for a symbol declared in a routine. The symbol uses
the same memory location in an y parallel DO -loops contained within the
routine .
If a routine has several concurren t invocations (because it is called from
within a parallel DO-loop), each invocation uses different memory locations for its variables that are declared CO NTEXT_SHARED.

The CONTEXT_SHARED directive takes the follo wing form:
CPAR$ CONTEXT_SHARED sy name [ , syname] .

syname
Is the name of a variable, array, or record declared within the routine .

Syntax Rules

In addition to the general compiler-directive syn tax rules listed in
Section 10.1 , CONTEXT_S HARED has the following speci fic rules:

10.2.2

•

CONTEXT_SHARED can appear anywhere within declaration statements in the routine.

•

Arrays cannot be dimensioned within CONTEXT_SHARED .

•

Symbols listed in CONTEXT_SHARED cannot also be listed in a
PRIVATE directive.

•

Dummy arguments cannot be declared CONTEXT_SHARED .

CPARS CONTEXT_SHAREO_ALL
The CONTEXT_SHARED_ALL directive fo rces all symbols that are
declared within a routine to default to CO NTEXT_S HARED . It takes the
following form:
CPAR$ CO NTEXT_ SHARED_ALL

This directive affects only default behavior. Individual symbols can still be
declared PRIVATE.
All general compiler-directive syntax rules apply to the CO NTEXT_
SHARED directive (see Section 10.1).

Compiler Directives

10- 3

10.2.3

CPARS oo_PARALLEL
The DO_P ARALLEL directive tells the compiler to run an indexed DOloop in parallel. It takes the following form:
CPAR$ DO _PARALLEL [count]

count
Is a numeric expression specifying the number of iterations in each set
distributed to processes running the DO-loop. Any remaining iterations
run in the last process. For example, if the total number of iterations is
1330, count is 100, and two processes are running the DO-loop, then each
process is distributed sets of 100 iterations at a time. The last set contains
the last 30 iterations.
The numeric expression must evaluate to a positive, non-zero integer. If
necessary, the process converts it to an integer by truncation. For example,
50 .56 is acceptable and is converted to 50. However, 0.20 is not acceptable
because it is converted to zero.
Syntax Rules

In addition to the general compiler-directive syntax rules listed in
Section 10.1, DO_PARALLEL and its corresponding DO-loop have the
following specific rules:

10-4

•

The indexed DO statement must be the next executable statement
following the DO_P ARALLEL directive. Only comments can appear
between the directive and its corresponding DO-loop.

•

The parallel DO-loop control variable must be a private integer. If it
is not specified PRIVATE, the compiler gives an informational message
and changes the control variable's default to PRIVATE. If the control
variable is not an integer, the compiler gives an error.

•

A parallel DO-loop cannot contain the following:

•

1/0 statements
PAUSE, RETURN, or STOP statements
Calls to system services or run-time library routines that modify
the con text of the process
A parallel DO-loop must not have a branch into or out of its body .

Compiler Directives

When calculations in parallel DO -loops require serial (sequential ) execu tion to achieve correct results, you must guard those calculations (called
critical regions) against parallel execution . This situation occurs w hen
calculations modify shared values that are needed in successive iterations
of the parallel DO-loop or elsewhere in the routine.
The following section describes the LOCKON and LOCKOFF directives,
which guard critical regions. See also the VAX FORTRAN User Manua l for
addi tional information.

10.2.4

CPARS LOCKON, CPARS LOCKOFF
The LOCKON and LOCKOFF directives enclose a region of execu table
code within a parallel DO-loop. They effectually force processes to
execute this critical region one at a time by excluding all other processes
from the region while one process is executing it.
A process executing the critical region "has the lock" while other processes
that want to execute it must wait un til it is free . The lock becomes fre e
when the process in the critical region executes the associated LOCKOFF
directive.
The LOCKON and LOCKOFF directives take the following forms :
CPAR$ LOCKON lck-var
(critical re gion)
CPAR$ LOCKOFF lck-var

/ck-var

Is a LOGJCAL*4 variable that can be any of the following items:

•
•

Scalar variable

•

Record field

•

Array element

Dummy argument

The lock variable (lck-var) must be in a shared common block or a
variable declared as CONTEXT_SHARED in the routine containing a
parallel DO-loop.
The lock variable is considered locked when it has a value of .TRUE . and
free when it has a value of .FALSE.

Compiler Directives

10-5

Syntax Rules

In addition to the general compiler-directive syntax rules listed in
Section 10.1, LOCKON and LOCKOFF have the following specific rules:

10.2.5

•

All LOCKON directives require an associated LOCKOFF directive that
executes in the DO-loop.

•

Statements in critical regions cannot transfer control outside the
region.

•

Lock variables can only have a LOGICAL*4 data type. Other data
types cause a compilation error.

•

Lock variables must be shared, either by specification or default. If
they are declared private, a compilation error results.

CPARS PRIVATE
The PRIVATE directive specifies the common blocks and symbols that
must be unique for each process that runs the parallel DO-loop. It takes
the following form:
CPAR$ PRIVATE name [,name] .

name
Is the name of a symbol or a common block (preceded and followed by
a slash). Common block names cannot exceed 26 characters; they can be
blank. Symbols can be an y variable name (scalar, array, or record) that is
declared within the routine .

Syntax Rules

In addition to the general compiler-directive syntax rules listed in
Section 10.1, PRIVATE has the following specific rules:

10-6

•

PRIVATE directives can appear anywhere within declaration statements in the routine.

•
•
•

Arrays cannot be dimensioned within this directive .

•

Symbols declared PRIVATE cannot also be declared CONTEXT_
SHARED.

Compiler Directives

Elements contained in a common block cannot be declared PRIVATE .
Common blocks that are declared PRIVATE cannot also be declared
SHARED .

•

10.2.6

•

Symbols can only be declared PRIVATE in routines containing a
parallel DO-loop.
Dummy arguments cannot be declared PRIVATE.

•

SAVE statemen ts cannot refer to PRIVATE symbols or common blocks.

CPARS PRIVATE-ALL
The PRIVATE-ALL directive forces all symbols and common blocks to
defaul t to PRIVATE in each process that runs the parallel DO -loop . It
takes the following form :
CPAR$ PRIVATE_ALL

The PRIVATE-ALL directive changes only default behavior. Individual
common blocks can still be declared SHARED and individual symbols can
still be declared CONTEXT_SHARED.
All general compiler-directive syntax rules apply to the PRIVATE-ALL
directive (see Section 10.1).

10.2.7

CPARS SHARED
The SHARED directive specifie s the common blocks that must be shared
between processes running a parallel DO-loop. It takes the followin g
form:
CPAR$ SHARED / [cb] / [ , /[cb ]/] ..

cb
Is the name of a common block. The na me cannot exceed 26 characters; it
can be blank.
Syntax Rules

In addition to the general compiler-directive syntax rules listed in
Section 10. 1, SHARED has the following specific rules:
•

SHARED directives can appear anywhere within declaration statem ents in the routine.

•

Common blocks that are declared SHARED cannot also be declared
PRIVATE.

Compiler Directives

10-7

10.2.8

CPARS SHARED-ALL
The SHARED_ALL directive forces all common blocks to have SHARED
defaults among processes that use the parallel DO-loop. It takes the
following form:
CPAR$ SHARED_ALL

This directive affects only default behavior. Individual common blocks can
still be declared PRIVATE.
All compiler-directive syntax rules apply to the SHARED_ALL directive
(see Section 10.1).

10.2.9

Parallel Directive Examples
The following examples demonstrate valid applications of parallel directives.
In the first example, assignment to the context-shared variables SUMA
and SUMB must be guarded from multiple processes attempting to write
to the variable at the same time . Th e LOCKON and LOCKOFF directives
accomplish this task by ensuring scalar execution of the statements.
CPAR$ PRIVATE I
CPAR$ SHARED /COM1/
CPAR$ CONTEXT_SHARED SUMA, SUMB
COMMON/COM1/A, B
INTEGER A(1 000) , B(1 000 ) , SUMA, SUMB
LOGICAL *4 LCK_VAR
CPAR$ DO_PARALLEL
DO I = 1 , 1000
CALL CALCULATE (I)
CPAR$ LOCKO N LCK_VAR
SUMA = SUMA + A(I)
SUMB = SUMB + B(I)
CPAR$ LOCKOFF LCK_VAR
ENDO
PRINT*, ' SUM A=', SUMA
PRINT*, ' SUM B=', SUMB
END

10-8

Compiler Directives

' Guard agai nst mult ipl e pr oces s es
writing to t he cont ext - shared
variab l e at the same t ime .

The second example uses valid SHARED, CONTEXT_SHARED, and
PRIVATE directives.
INTEGER A(1000 ) . 8(1000)
COMMO N/COM1 / B
PARAMETER (N = 1000)
CPAR$ SHARED_ALL
CPAR$ CONTEXT_SHARED ALL
CPAR$ PRIVATE I

' Reinforces the SHARED default for
' common blocks .
1 Reinforces the CO NTEXT_SHARED default
' for local symbols .
1

Loop control must be pri vat e .

CPAR$ DO_PARALLEL
DO 10 I = 1 , N

A(I)

A(I) + I

B(I)

A(I)

CONTI NUE
CALL SUBR(A , N)
WRITE (5 ,* ) A, B
END

c
SUBROUTI NE SUBR(A , N)
I NTEGER A( N) . 8(1000)
COMMON/ COM1/B
CPAR$ SHARED /COM1/
CPAR$ PRIVATE_ALL

' The common block must be SHARED .
t M
ake the default PRIVATE .

CPAR$ DO_PARALLEL N/2
DO J = 1 , N

Di s t ributes half of the iterations to
' each of two processors .

A(J)

B(J) + J

ENDO
RETURN
END

Compiler Directives

10-9

10.3 General Directives
General directives label or modify certain entities. No qualifier is needed
on the FORTRAN command line to enable general directives.
General directives take the following form :
co l umn 1

CDEC$ di r ecti ve

directive
Is any one of the following values:
•

!DENT-provides identification of an object module.

•

PSECT-modifies certain attributes of a common block.

•

TITLE, SUBTITLE-provides a listing header.

10.3. 1 CDECS IDENT
The IDENT directive specifies a string that can be used to identify an
object module. The compiler places the string in the identification field of
an object module when it generates the module for each source program
unit. The IDENT directive takes the following form:
CDEC$ IDENT string

string
Is a group of up to 31 printable characters delimited by apostrophes .
Syntax Rules

In addition to the general compiler-directive syntax rules listed in
Section 10.1, IDENT has the following specific rules:
•

Only the first IDE NT directive is effective-the compiler ignores any
additional IDENT directives in a program unit.

•

IDENT has no effect when you specify /NOOBJECT on the FORTRAN
command line.

10-1 0 Compiler Directives

10.3.2

COE CS PSECT
The PSECT directive modifies several attributes of a common block. It
takes the following form:
CDEC$ PSECT /commo n-name/ attr [,at tr] .. .

common-name
Is the name of the common block, preceded and follo wed by a slash.

attr
Is one of th e following attributes:

•
•
•
•

•

LCL-local scope; opposite to GBL and cannot appear with it
GBL-global scope
[NO]WRT-writabili ty or no-writability
[NO]SHR-shareability or no-shareability
ALIGN=val-alignment for the common block; val must be a constant
ranging from 0 thru 9

Syntax Ru les

In addition to the general compiler-directive syntax rules listed in
Section 10.1, PSECT has the following specific rules:
•

If one program unit changes one or more attributes, all other units
that reference the common block must also change those attributes in
the same way.

•

Default attributes apply if you do not modify them with a PSECT
directive. Table 10-1 lists the default attributes of common blocks and
how they can be modified by PSECT.

Compiler Directives

10-11

Table 10-1:

Common Block Default Attributes and PSECT
Modifi cation

Common Block Default Attributes

PSECT Modification

Relocatability

none

Overlaid

non e

Global Scope

Gl obal or local scope

No executability

none

Writability

Writability or no- writabili ty

Readability

none

Position independence

none

Shareability

Shareability or no-shareability

No protection

none

LONGWORD alignment (2)
(FORTRAN d efault)

0 thru 9

Global or loca l scope is significant for an image that has more than one
cluster. The attribute determines whether program sections with the same
name but from differen t modules in different clusters are finally placed in
separate clusters (local scope) or in the same cluster (global scope).
[No]writability determines whether the contents of a common block can be
modified during program execution .
[No]shareability determines whether the contents of a common block can
be shared by more than one process.
ALIGN= val aligns the common block. The specified number is interpreted
as a power of 2. The value of the expression is the alignment in bytes: a
value of 0 specifies BYTE alignment; a value of 9 specifies page alignment.
Refer to the VMS Linker Utility Manual fo r detailed information about
default attributes of common blocks.

10-12

Compiler Directives

10.3.3

CDECS TITLE, CDECS SUBTITLE
The TITLE directive specifies a string and places it in the title field of a
listing header. Similarly, SUBTITLE places a specified string in the subtitle
field of a listing header.
These directives take the following forms:
CDEC$ TITLE s t r ing
CDEC$ SUBTI TLE s t r ing

string
Is a group of up to 31 printable characters delimited by apostrophes.

Syntax Rules

In addition to the general compiler-directive syntax rules listed in
Section 10.1, TITLE and SUBTITLE have the following specific rules:

•

To enable TITLE and SUBTITLE directives, you must specify / LIST on
the FORTRAN command line.

•

When TITLE or SUBTITLE appear on a page of a listing file, the
specified string appears in the listing header of the following page.
If two or more of either directives appear on a page, the last directive
is the one in effect for the foll owing page.

•
•

If either directive does not specify a string, no change occurs in the
listing file header.

Compiler Directives

10-13

Appendix A

Additional Language Features
To facilitate compatibility with other versions of FORTRAN, VAX
FORTRAN provides the following additional language features:
•
•

ENCODE, DECODE, DEFINE FILE, and FIND statements
Alternative syntax for the PARAMETER statement and octal constants

•

A /NOF77 interpretation of the EXTERNAL statement

These language features are particularly useful in transporting older
FORTRAN programs to a VAX system. However, you should avoid using
them in new programs on VAX systems and in new programs for which
portability to other FORTRAN-77 implementations is important.

A.1

The ENCODE and DECODE Statements
The ENCODE and DECODE statements transfer data between variables
or arrays in internal storage. The ENCODE statement translates data
from internal (binary) form to character form. Inversely, the DECODE
statement translates data from character to internal form. These statements
are comparable to using internal files in formatted sequential WRITE and
READ statements, respectively.
The ENCODE and DECODE statements take the following forms:
ENCODE (c. f. b [. IOSTAT=ios] [, ERR=s])

[list]

DECODE (c, f, b [, IOSTAT=ios] [, ERR=s])

[list]

Additional Language Features

A-1

c
Is an integer expression . In the ENCODE statement, c is the number of
characters (in bytes) to be translated to character form . In the DECODE
statement, c is the number of characters to be translated to internal form .
f

Is a format identifier. An error occurs if more than one record is specified.

b
Is a scalar or array name reference. If b is an array name reference, its
elements are processed in the order of subscript progression.
In the ENCODE statement, b receives the characters after translation
to extern al form . If less than c characters are received, the remaining
character positions are filled with blank characters. In the DECODE
statement, b contains th e characters to be translated to internal form.
ios
Is an integer scalar memory reference that is defined as a positive integer
if an error occurs, and zero if no error occurs.

s
Is the label of an executable statement.
list
Is an I/O list.

In the ENCODE statement, the list contains the data to be transla ted to
character fo rm . In the DECODE statement, the list receives the data after
translation to internal form .
The interaction between the fo rmat specifier and the I/O list is the same
as for a formatted I/O statement.
Syntax Rules and Behavior

The number of characters that the ENCODE or DECODE statement can
process depends on the data type of b. For example, an INTEGER*2 array
can contain two characters per element, so that the maximum number
of characters is twice the number of elements in that array. A character
variable or character array element can contain characters equal in number
to its length . A character array can contain characters equal in number to
the length of each element multiplied by the number of elements.

A-2

Additional Language Features

Examples

In the following example, the DECODE statement translates the 12
characters in A to integer form (as specified by FORMAT 100):

100

DIMEN SIO N K(3)
CHARACTER*12 A,B
DATA A/ '123456789012 ' /
DECODE (1 2 , 100, A) K
FORMAT (3I4 )
ENCODE (12,100, B) K(3) , K(2), K(1)

The 12 characters are stored in arra y K:
K( 1) = 1234
K(2) = 5678
K(3) = 901 2

The ENCODE statement translates the values K(3 ), K(2), and K(l) to
character form and stores the characters in the character variable B:
B = '90 125678 1234'

A.2 DEFINE FILE Statement
The DEFINE FILE statem ent establishes the size and structure of files
with relative organization and associates them with a logical unit number.
The DEFINE FILE statement is comparable to the OPEN statement (in
situations where you can use the OPEN statement, it is the preferable
mechanism for creating and opening files) .
The DEFINE FILE sta tement takes the foll owing form :
DEFI NE FILE u (m, n ,U,asv )[, u (m, n ,U, asv ) ] . ..

u
Is an integer constant or variable that specifies the logical unit number.

m
Is an integer constant or variable that specifies the number of records in
the fil e.

n
Is an integer constant or variable that specifi es the length of each record in
16-bit words (2 bytes).

Additional Language Features

A-3

u
Specifies that the file is unformatted (binary); this is the only acceptable
entry in this position.

asv
Is an integer variable, called the associated variable of the file. At the end
of each direct access I/O operation, the record number of the next higher
numbered record in the file is assigned to v; asv must not be a dummy
argument.
Syntax Rules and Behavior

The DEFINE FILE statement specifies that a file containing m fixed-length
records, each composed of n 16-bit words, exists (or is to exist) on the
specified logical unit. The records in the file are numbered sequentially
from 1 through m.
A DEFINE FILE statement must be executed before the first direct access
I/O statement referring to the specified file, even though the DEFINE FILE
statement does not itself open the file. The file is actually opened when
the first direct access I/O statement for the unit is executed. If this I/O
statement is a WRITE statement, a new relative organization file is created.
If it is a READ or FIND statement, an existing file is opened, unless the
specified file does not exist. If a file does not exist, an error occurs.
The DEFINE FILE statement establishes the integer variable asv as the associated variable of a file . At the end of each direct access I/O operation,
the FORTRAN I/O system places in asv the record number of the record
immediately following the one just read or written. Because the associated
variable always points to the next sequential record in the file (unless the
associated variable is redefined by an assignment, input, or FIND statement), direct access I/O statements can perform sequential processing on
the file . They do this by using the associated variable of the file as the
record number specifier.
Example

In the following example, the DEFINE FILE statement specifies that the
logical unit 3 is to be connected to a file of 1000 fixed-length records;
each record is forty-eight 16-bit words long. The records are numbered
sequentially from 1 through 1000 and are unformatted. After each direct
access I/O operation on this file , the integer variable NREC will contain
the record number of the record immediately following the record just
processed.
DEFI NE FILE 3 (1000 ,48 ,U, NREC )

A-4 Additional Language Features

A.3 FIND Statement
The FIND statement positions a direct access file at a particular record
and sets the associated variable of the file to that record nu mber. It is
comparable to a direct access READ statement with no 1/0 list, and can
open an existing file. No data transfer takes place. (See the description
of the OPEN statement's ASSOCIATEVARIABLE keyword or the DEFINE
FILE statement for information about associate variables.)
The FIND statement takes one of the following forms:
FIND (u'r[ , ERR=s ] [ , IOSTAT= ios ])
FI ND ( [UNIT=]u,REC=r[,ERR=s] [, I OSTAT= i os] )

u
Is a logical unit number. It must refer to a relative organization file .

r
Is the direct access record number. It cannot be less th an one or greater
than the number of records defined for the file .

s
Is the label of the executable statement that receives control if no error
occurs.
ios

Is an integer variable or integer array element that is defined as a positive
integer if an error occurs, and as a zero if no error occurs.
Examples

In the first example, the FIND statement positions logical unit 1 at the firs t
record in the file. The file's associated variable is set to one :
FI ND (1' 1)

In the second example, the FIND statement positions the file at the record
identified by the content of INDX. The file's associated variable is set to
the value of INDX:
FI ND (4'I NDX)

Additional Language Features

A-5

A.4 PARAMETER Statement
The P ARAMETER statement discussed here is similar to the one discussed
in Section 4. 11; they both assign a symbolic name to a constant. However,
this PARAMETER statement differs from the other one in the following
two ways: its list is not bounded with parentheses; and the form of the
constant, rather th an implicit or explicit typing of the symbolic name,
determines th e data type of the variable .
This PARAMETER statement takes the following form:
PARAMETER p=c [,p=c] ...

p
Is a symbolic name .

c
Is a constant, the symbolic name of a constant, or a compile-time constant
expression .
Syntax Rules and Behavior

Each symbolic name (p) becomes a constant and is defined as the value of
the constant or constant expression (c) . Once a symbolic name is define d
as a constant, it can appear in any position in which a constant is allowed .
The effect is the same as if the constant were written there instead of the
symbolic name.
The symbolic name of a constant cannot appear as part of another constant, but it can appear as a real or imaginary part of a complex constant.
Compile-time constant expressions are defined in Section 4. 11.
You can use symbolic names in a PARAMETER statement only to identify
the symbolic name's corresponding constant in that program unit. Such
a name can be defined only once in PARAMETER statements within the
same program unit.
The symbolic n ame of a constant assumes the data type of its corresponding constant expression . The data type of a parameter constant cannot be
specified in a type declaration statement. Nor does the initial letter of the
constant's name implicitly affect its data type .

A-6

Additional Language Features

Exa mples
PARAMETER PI=3 . 1415927 , DPI=3 . 141592653589793238DO
PARAMETER PIOV2=PI/2, DPIOV2=DPI/2
PARAMETER FLAG= . TRUE ., LONGN AME=' A STRING OF 25 CHARACTERS'

A.5

Octal Notation for Integer Constants
Octal forms of integer constants allow compatibility with PDP-11
FORTRAN.
An octal integer constant takes the following form :
"nn

nn
Is a string of digits in the range 0 to 7.
Examples

The following examples demonstrate valid and invalid octal integer
constants and explain w hy the invalid ones are not valid:
Valid
"107
"1 77777

Invalid

Explanation

" 108

Contains a digit outside the allowed range

"1377 .

Contains a decim al poin t

"17777"

Contains a trailing quotation mark

These octal forms are not the same as the typeless octal constants discussed in Section 2.2.1.4. Integer constants in octal form have integer data
type and are trea ted as integers .

Additional Language Features

A-7

A.6 /NOF77 Interpretation of the EXTERNAL Statement
By using the /NOF77 qualifier on the FORTRAN command line, you can
obtain another interpretation of the EXTERNAL statement. This additional
interpretation facilitates compatibility with older versions of FORTRAN
due to the ANSI FORTRAN-77 interpretation being incompatible with the
previous Standard and previous DIGITAL implementations.
The / NOF77 interpretation of the EXTERNAL statement combines the
function of the INTRINSIC statement with that of the EXTERNAL statement discussed in Section 4.7. It is available only if the /NOF77 qualifier
is specified on the FORTRAN command line.
The /NOF77 EXTERNAL statement lets you use subprograms as arguments to other subprograms. The subprograms to be used as arguments
can be either user-supplied procedures or FORTRAN library functions .
The /NOF77 EXTERNAL statement takes the following form:
EXTERNAL [ *] v [ . [ *] v ] . ..

v
Is th e symbolic name of a subprogram or the name of a dummy argument
associated with the symbolic name of a subprogram.

Specifies that a user-supplied function is to be used instead of a FORTRAN
library function having the same name . See Section 6.3 for information on
FORTRAN library functions (intrinsic functions) .
Syntax Rules and Behavior

The / NO F77 EXTERNAL statement declares that each symbolic name in
its list is an external procedure name . Such a name can then be used as an
actual argument to a subprogram, which in turn can use the corresponding
dummy argument in a function reference or CALL statement.
However, used as an argument, a complete function reference represents
a value, not a subprogram name; for example, SQRT(B) in CALL SUBR(A,
SQRT(B), C). It is not, therefore, defined in an EXTERNAL statement (as
would be the incomplete reference SQRT) .

A-8

Additional Language Features

Example

The following example uses the /NOF77 EXTERNAL statement:
Main Program

Subprograms

EXTERNAL SI N, COS, *TAN, SI NDEG

SUBROUTI NE TRIG(X , F,Y)
Y = F(X )
RETURN

CALL TRIG( ANGLE ,SI N,S I NE)

END

CALL TRIG(ANGLE,COS,COSI NE)

FUNCTION TAN(X)
CALL TRIG( ANGLE,TAN,TANGNT)

TAN= SIN(X)/COS(X)
RETURN
END

CALL TRIG(ANGLED,SI NDEG ,SI NE)
FUNCTION SI NDEG(X )
SI NDEG = SI N(X*3 . 1459/180)
RETURN
END

The CALL statements pass the name of a fu nction to the subroutine TRIG.
The function reference F(X) subsequently invokes the function in the
second statement of TRIG. Depending on which CALL statement invoked
TRIG, the second statement is equivalent to one of the following:
Y = SI N( X)
Y = COS (X)
Y = TAN( X)
Y = SI NDEG (X)

The functions SIN and COS are examples of trigonometric functions
supplied in the FORTRAN library. Th e fun ction TAN is also supplied in
the library. But the asterisk in the EXTERNAL statement specifies that
the user-supplied function be used, instead of the library function. The
function SINDEG is also a user-supplied function. Because no library
function has the same name, no asterisk is required .

Additional Language Features

A-9

Appendix B

Character Sets
This appendix describes the following three character sets:
•
•
•

FORTRAN
ASCII
Radix-50

B. 1 FORTRAN Character Set
The FORTRAN character set consists of the following:
•
•
•

All upper- and lowercase letters (A through Z, a through z)
The numerals 0 through 9
The following special characters:

Character Sets 8-1

Character

Name

ti or < TAB >

Space or tab

Apostrophe

Equal sign

Quotation mark

Plus sign

Character

Name

Dollar sign

Minus sign

Underscore

Asterisk

Exclamation point

Slash

Colon
Left angle bracket

Right parenthesis

<
>

Comma

Percent sign

Period

Ampersand

Left parenthesis

Right angle bracket

Other printing characters can appear in a FORTRAN statement only as
part of a Hollerith or character constant. Any printing character can
appear in a comment. Printing characters are characters whose ASCII
codes are in the range 20 through 7D. See Table B-1.

B.2 ASCII Character Set
Table B-1 represents the ASCII character set. At the top of the table are
hexadecimal digits (0 to 7), and to the left of the table are hexadecimal
digits (0 to F). To determine the hexadecimal value of an ASCII character,
use the hexadecimal digit that corresponds to the row in the "units"
position, and use the hexadecimal digit that corresponds to the column in
the "16s" position. For example, the value of the character representing
the equal sign is 3D.

B-2

Character Sets

Table B-1:

ASCII Character Set
Column

Row

NUL

OLE

SOH

DC1

7
p

STX

DC2

ETX

DC3

EOT

DC4

5
6
7
8

ENO

NAK

ACK

SYN

ETB

CAN

v
w
x

BEL

5
6
7
8

SUB

ESC

[

y
J
k

DEL

NUL

Null

OLE

Data Link Escape

SOH

Start of Heading

DC1

Device Control 1

STX

Start of Text

DC2

Device Control 2

ETX

End of Text

DC3

Device Control 3

EOT

End of Transmission

DC4

Device Control 4

ENO

Enquiry

NAK

Negative Acknow ledge

ACK

Acknowledge

SYN

Synchronous Idle

BEL

Bell

ETB

End of Transmission Block

Backspace

CAN

Cancel

Horizontal Tabulation

End of Medium

Line Feed

SUB

Substitute

Vertical Tab

ESC

Escape

Form Feed

File Separator

Carriage Return

Group Separator

Shift Out

Record Separator

Shift In

Unit Separator

Space

DEL

Delete
ZK-7458-HC

Character Sets B-3

B.3 Radix- 50 Constants and Character Set
Radix-50 is a special character data representation in which up to 3 ch aracters can be encoded and packed into 16 bits. The Radix- 50 character
set is a subset of the ASCII character set and is provided for compatibility
with PDP-11 FORTRAN.
The Radix- 50 characters and corresponding values are given in
Table B- 2.
Table B-2:

RADIX-50 Character Set with Comparative
V alues

Character

ASCII Octal Equivalen t

Radix-SO O ctal Value

Space

A -Z

101 - 132

1 - 32

(Unassigned)
0 - 9

35
60 - 71

36 - 47

Radix-50 values are stored, u p to three characters per word, by packing
them into single numeric values according to the following formula:
( (i * 50 + j ) * 50 + k)

The values i, j, and k represent the code values of the three Radix- 50
characters. Thus, the maximum Radix-50 value is as follows:
47 * 50 * 50 + 47 * 50 + 47 = 174777
A Radix-50 constant takes the following form :
nRc1 c2 . . . e n

B-4 Character Sets

n
Is an u nsigned, nonzero integer constant that states the number of characters to follow .

c
Is a character from the Radix- SO character set.
The maximum number of characters is 12. The character count must
include any spaces tha t appear in the character string (the space character
is a valid Radix- SO character). You can use Radix- SO constants only in
DATA statements .
When a Radix-50 constant is assigned to a numeric variable or array
element, the n umber of bytes that can be assigned depends on the data
type of the com ponent (see Table 2- 1). If the Radix-SO constant contains
fewer bytes than the length of the component, ASCII null characters (zero
bytes) are appended on the right. If the constant con tains more bytes than
the length of the component, the righ tm ost characters are not used .
Examples

The foll owing examples illustrate valid and invalid Radix-SO constants
an d explain wh y the invalid ones are not valid:
Valid
4RABCD

6R6T066 6
Invalid

Explanation

4RDKO :

colon is n ot a Radix-SO character

Character Sets

B-5

Appendix C

FORTRAN Data Representation
This appendix describes the data types supported by VAX FORTRAN
and illustrates how they are stored in memory. The symbol :A in any
illustration specifies the address of the byte containing bit 0, which is the
starting address of the represented data element.

C.1

INTEGER*2 Representation
15 14

~'~-'~'~~~~B-l_N_A_R_Y~N-U_M_B_E_R~~~~~-''

ZK -798-82

SIGN = O(+) . 1(-)

Integers are stored in a twos complement representation. INTEGER•2
values are in the range -32768 to 32767, and are stored in two contiguous
bytes aligned on an arbitrary byte boundary. For example:
+22 = 0016(hex)
-7 = FFF9(hex)

FORTRAN Data Representation

C-1

C.2 INTEGER*4 Representation
31 30

ZK-799-82

SIGN= 0(+), 1(-)

INTEGER•4 values are stored in twos complement representation and lie
in the range -2147483648 to 2147483647. Each value is stored in four
contiguous bytes, aligned on an arbitrary byte boundary. Note that if the
value is in the range of an INTEGER•2 value (-32768 to 32767), then the
first word can be referenced as an INTEGER•2 value.

C.3 LOGICAL* 1 (BYTE) Representation
7

0
BINARY NUMBER

ZK-797-82

LOGICAL•l (or BYTE) values are in the range -128 to 127.

C.4 LOGICAL*2 and LOGICAL*4 Representation
Logical values are stored in two (LOGICAL•2) or four (LOGICAL•4)
contiguous bytes, starting on an arbitrary byte boundary. The low-order
bit (bit 0) determines the value. If bit 0 is set, the value is .TRUE. If bit 0
is clear, the value is .FALSE.

C-2 FORTRAN Data Representation

LOGICAL•2
15
TRUE :

1 0

..___ _ _ _u_N_D_E_F_IN-E-D-Bl_T_s_ _ ___._J'_.J

15
FALSE :

1 0
UNDEF I NED BITS
ZK- 802-8 2

LOGICAL•4
1 0

15
TRUE :

UNDEFINED BITS

:A+2
16

15
FALSE :

1
UNDEFINED BITS

0
0

:A+2

UNDEFINED BITS
31

16
ZK-803-82

C.5

Floating-Point Representations
The exponent for the REAL•4 and REAL•8 (D_floating) formats is stored
in binary excess 128 notation. Binary exponents from -127 to 127 are
represented by the binary equivalents of 1 through 255.

FORTRAN Data Representation

C-3

The exponent for the REAL*8 (G_floating) format is stored in binary
excess 1024 notation. The exponent for the REAL*l6 format is stored
in binary excess 16384 notation. In REAL*8 (G_floating) format, binary
exponents from -1023 to 1023 are represented by the binary equivalents
of 1 through 2047. In REAL*l6 format, binary exponents from -16383 to
16383 are represented by the binary equivalents of 1 through 32767.
For each floating-point format, fractions are represented in sign-magnitude
notation, with the binary radix point to the left of the most significant bit.
Fractions are assumed to be normalized, and therefore the most significant
bit is not stored (this is called "hidden bit normalization"). This bit is
assumed to be 1 unless the exponent is 0. If the exponent equals 0, then
the value represented is either zero, or it is a reserved operand. (Refer to
the VAX FORTRAN User Manual for an explanation of the representation
of 0.0 and reserved operand faults.)

C.5. 1 REAL•4 (f_floating)
REAL*4 (F_floating) data is four contiguous bytes starting on an arbitrary
byte boundary. Bits are labeled from the right, 0 through 31.
7

15 14

I
G
N

EXPONENT

FRACTION

:A+2

FRACTION
31

16
ZK-800-82

SIGN = 0(+) , 1(-)

The form of REAL*4 (F_floating) data is sign magnitude, with bit 15 the
sign bit, bits 14:7 an excess 128 binary exponent, and bits 6:0 and 31:16 a
normalized 24-bit fraction with the redundant most significant fraction bit
not represented. The value of F_floating data is in the approximate range:
0.29*10**-38 through l.7*10**38. The precision is approximately one part
in 2**23; that is, typically, seven decimal digits.

C-4 FORTRAN Data Representation

C.5.2

REAL•B (D_floating)
REAL•8 (D_floating) data is eight contiguous bytes starting on an arbitrary
byte boundary. Bits are labeled from the right, 0 through 63 .
7 6

15 14

I
G

EXPONENT

FRACTION

:A+2

FRACTION

:A+4 .

FRACTION

:A+6

48
ZK-801- 82

SIGN = 0(+), 1(-)

The form of REAL•8 (D_floating) data is identical to an F_floating real
number, except for an additional 32 low-significance fraction bits. The
exponent conventions and approximate range of values are the same as
those for F_floating. The precision is approximately one part in 2**55;
that is, typically, 16 decimal digits.

FORTRAN Data Representation

C-5

C.5.3

REAL*B (G_floating)
REAL*8 (G_floating) data is eight contiguous bytes starting on an arbitrary byte boundary. The bits are labeled from the right, 0
through 63.

15 14

s
I

EXPONENT

FRACTION

:A+2

FRACTION

:A+4

FRACTION

:A+6

48
ZK-804-82

SIGN = 0(+) , 1( - )

The form of REAL*8 (G_floating) data is sign magnitude, with bit 15 the
sign bit, bits 14:4 an excess 1024 binary exponent, and bits 3:0 and 63 :16
a normalized 53-bit fraction with the redundant most significant fraction
bit not represented. The value of a G_floating data is in the approximate
range 0.56*10**-308 through 0.9*10**308. The precision of G_floating
data is approximately one part in 2**52; that is, typically, 15 decimal
digits.

C-6

FORTRAN Data Representation

C.5.4

REAL* 16 (H _floating)
REAL•16 (H_floating) data is 16 contiguous bytes starting on an arbitrary
byte boundary. The bits are labeled from the right, 0 through 127.
0

15 14

s
I

EXPONENT

FRACTION

:A+2

FRACTION

:A+4

FRACTION

:A+6

FRACTION

:A+8

FRACTION

:A+10

FRACTION

:A+12

FRACTION

:A+14

127

112
ZK-805-82

SIGN = 0(+) . 1(-)

The form of a REAL•16 (H_floating) data is sign magnitude with bit 15
the sign bit, bits 14:0 an excess 16384 binary exponent, and bits 127:16 a
normalized 113-bit fraction with the redundant most significant fraction bit
not represented. The value of H_floating data is in the approximate range
0.84•10**-4932 through 0.59•10**4932. The precision of H_floating data
is approximately one part in 2**112; that is, typically, 33 decimal digits.
FORTRAN Data Representation

C-7

C.5.5

COMPLEX•B (f_floating)
COMPLEX•8 data is eight contiguous bytes aligned on an arbitrary byte
boundary. The low-order four bytes contain REAL•4 data that represents
the real part of the complex number. The high-order four bytes contain
REAL•4 data that represents the imaginary part of the complex number.
15 14

I
G
N

REAL PART

EXPONENT

FRACTION

:A+2

I
G
N

IMAGINARY PART

EXPONENT

FRACTION

:A+4

FRACTION

:A+6

48
ZK-806-8 2

SIGN = 0(+) . 1(-)

C.5.6

COMPLEX•16 (D_floating)
COMPLEX•16 (D_floating) data is 16 contiguous bytes aligned on an
arbitrary byte boundary. The low-order eight bytes contain REAL•8
(D_floating) data that represents the real part of the complex data . The
high-order eight bytes contain REAL•8 (D_floating) data that represents
the imaginary part of the complex data.

C-8

FORTRAN Data Representation

15 14

I
G
N

FRACTION

EXPONENT

FRACTION

:A+2

FRACTION

:A+4

FRACTION

:A+6

REAL PART

I
G
N

EXPONENT

:A+8

FRACTION

:A+10

FRACTION

:A+12

FRACTION

:A+14

IMAGINARY PART

127

112
ZK-807-82

SIGN= O(+), 1(-)

FORTRAN Data Representation

C-9

C.5.7

COMPLEX•16 (G_floating)
COMPLEX•16 (G_floating) data is 16 contiguous bytes aligned on an
arbitrary byte boundary. The low-order eight bytes contain REAL•8
(G_floating) data that represents the real part of the complex data. The
high-order eight bytes contain REAL•8 (G_floating) data that represents
the imaginary part of the complex data.
15 14

I
G
N

EXPONENT

FRACTION

:A+2

FRACTION

:A+4

FRACTION

:A+6

REAL PART

I
G
N

EXPONENT

:A+8

FRACTION

:A+10

FRACTION

:A+12

FRACTION

:A+14

IMAGINARY PART

127

112
ZK-808-82

C-10

FORTRAN Data Representation

C.6 Character Representation
A character string is a contiguous sequence of bytes in memory.

CHAR 1

•
•
•
CHAR L

:A+L-1

ZK-809-82

A character string is specified by two attributes: the address A of the first
byte of the string, and the length L of the string in bytes. The length L of
a string is in the range 1 through 65535.

C. 7 Hollerith Representation
Hollerith constants are stored internally, one character per byte.

FORTRAN Data Representation

C-11

1 Byte
7

0
CHAR 1

2 Bytes
87

15
CHAR 2

CHAR 1

4 Bytes
31

16 15

24 23
CHAR 4

CHAR 3

8 7
CHAR 2

CHAR 1

8 Bytes
15

8 7
CHAR 2

CHAR 1

CHAR 4

CHAR 3

:A +2

CHAR 6

CHAR 5

:A +4

CHAR 8

CHAR 7

:A +6

56 55

48
ZK-810-82

C-12 FORTRAN Data Representation

Appendix 0

VAX FORTRAN Language Summary
This appendix summarizes VAX FORTRAN expression operators
(Table D-1), statements (Table D-2), and intrinsic functions (Table D-3).
It also describes the system subroutines provided with VAX FORTRAN
(Section D.4) and discusses the intrinsic functions available for manipulating bits in integer data items (Section D.5).

0. 1 Expression Operators
This section lists the expression operators in each data type in order of
descending precedence:
Table D-1: Expression Operators
Data Type
Operator Operation
Arithmetic

Operates Upon

Exponen tia ti on

•, I

Multiplication, division

+ -

Addition, subtraction,
unary plus and minus

Character

Concatenation

Character expressions

Relational

.GT.
.GE.

Greater than
Greater than or equal to

Arithmetic, logical, or
character expressions (all
relational operators have
equal precedence)

.LT.

Less than

Arithmetic or logical
expressions

VAX FORTRAN Language Summary

0-1

Table D-1 (Cont.):

Expression Operators

Data Type

Operator

Operation

.LE.

Less than or equal to

.EQ.

Equal to

.NE .

Not equal to

.NOT.

.NOT.A is true only if A
is false

.AND.

A.AND.B is true only if
A and B are both true

.OR.

A.OR.B is true if either A
or B or both are true

.EQV.

A.EQV.B is true only if A
and B are both true or A
and B are both false

.NEQV.

A.NEQV.B is true only if
A is true and B is false or
B is true and A is false

.XOR.

Same as .NEQV.

Logical

Operates Upon

Logical or integer expressions

.EQV., .NEQV., and .XOR .
have equal priority

0.2 Statements
This section summarizes the statements available in the VAX FORTRAN
language, including the general form of each statement. The statements
are listed alphabetically for ease of reference.

D-2

VAX FORTRAN Language Summary

Table D-2:

VAX FORTRAN Language

Statement Summary
ACCEPT
See READ statements (sequential access).
See Section 7.5 .

ASSIGN s TO v
s

is the label of an executable statement or a FORMAT statement.

is an integer variable name .

Associates the statement label s with the integer variable v for later use as a
format specifier or in an assigned GO TO statement.
See Section 3.4.

Assignment Statement
v=e
v

is a scalar memory reference or an aggregate reference .

is an expression or an aggregate .

The assignment statement assigns the value of the arithmetic, logical, or character
expression on the right of the equal sign to the corresponding numeric, logical,
or character scalar memo~y reference on the left. If aggregates are involved, the
aggregate re ference and the aggregate must h ave matching stru ctures.
See Sections 3.1 - 3.3.

BACKSPACE ([UNIT=]u[,ERR=s][,IOSTAT=ios])
BACKSPACE u
u

is a logical unit specifier.

is the label of an executable statement.

ios

is an 1/0 status specifier.

The BACKSPACE statement backspaces the currently open file on logical unit u
by one record .
See Section 9.5.

BLOCK DAT A [nam]
nam

is a symbolic name.

The BLOCK DATA statement specifies the subprogram that follows as a BLOCK
DATA subprogram.
See Section 4.1.

VAX FORTRAN Language Summary

D-3

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
CALL sub[([a][,[a]] ... )]
sub

a subprogram name or entry point name.

is an expression, an array name, a procedure name, or an alternate
return specifier. An alternate return specifier is •s or &s, where s is
the label of an executable statement.

The CALL statement calls the subroutine subprogram with the name specified
by sub, passing the actual arguments (a) to replace the dummy arguments in the
subroutine definition.
See Sections 5.1 and 6.2.3.
CDEC$ !DENT string
string

is a group of up to 31 printable characters delimited by apostrophes.

The IDENT directive specifies a string that identifies an object module.
See Section 10.3.1.
CDEC$ PSECT /common-name/ attr [,attr] ...
commonname

is the name of the common block, which must be preceded and
fo llowed by a slash .

attr

is one of the fo llowing attributes: LCL (local scope); GBL (global
scope); [NO]WRT (writability or no writability); [NO]SHR (shareability or no shareability); or ALIGN = val (alignment for the common
block, val must be a constant ranging fro m 0 thru 9).

The PSECT directive modifies certain attributes of a common block.
See Section 10.3.2 .
CDEC$ SUBTITLE string
string

is a group of up to 31 printable characters delimited by apostrophes.

The SUBTITLE directive crea tes a header in a listing's subtitle field .
See Section 10 .3.3 .
CDEC$ TITLE string
string

is a group of up to 31 printable characters delimited by apostrophes.

The TITLE directive creates a header in a listing's title fi eld .
See Section 10 .3.3.
CLOSE ((UNIT=]u[,p][,ERR=s][,IOSTAT=ios])
u

0-4

is a logical unit specifier.

VAX FORTRAN Language Summary

Table D-2 (Cont.):
Statement Summary
p

VAX FORTRAN Language

is one of the following parameters:
'SAVE'
'KEEP'
'DELETE'
STATUS
'PRINT'
{ DISPOSE
'SUBMIT'
DISP
'PRINT /DELETE '
'SUBMIT /DELETE'

is the label of an executable statement.

ios

is an I/O status specifier.

The CLOSE statement closes the specified file .
See Section 9.2.
COMMON [/[cb]/]nlist[[,] /[cb]/nlist] ...
cb

is a common block name.

nlist

is a list of one or more variable names, array names, array declarators, or records separated by commas.

The COMMON statement reserves one or more blocks of storage space to contain
the variables associated with a specified block name.
See Section 4. 2.
CONTINUE
The CONTINUE statement transfers control to the next executable statement.
See Section 5. 2.
CP AR$ CONTEXT_SHARED syname [,syname )...
syname

is the name of a variable, array, or record declared within the
routine.

The CP AR$ CONTEXT_SHARED directive specifies shared memory locations for
symbols declared in the routines compiled with the /PARALLEL qualifier.
See Section 10.2.1.
CP AR$ CONTEXT_SHARED_ALL
The CP AR$ CONTEXT_SHARED_ALL directive reinforces the context-shared
default of symbols in routines compiled with the /PARALLEL qualifier.
See Section 10.2.2.
CPAR$ oo_pARALLEL [count)

VAX FORTRAN Language Summary

0-5

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary

count

is a numeric expression specifying the number of iterations in each
set distributed to processors running the parallel DO-loop. The
nu mber must be able to be evaluated as a positive, non-zero integer.

Th e DO_PA RALLEL directive enables parallel processing of the DO-loop that
foll ows it.
See Section 10.2 .3.
CP AR$ LOCK ON kk-var

(critical region)
CP AR$ LOCK OFF lck- var

lck-var

is a scalar memory reference with a LOGICAL*4 data type.
The LOCKON and LOCKOFF directives enclose a critical
region of executable code within a parallel DO-loop and
permit only one process at a time to execute the region.

See Section 10. 2 .4.
CP AR$ PRIVATE name (,name] ...

name

is the name of a symbol or a common block (preceded and followed
by a slash).

The CPAR$ PRIVATE directive specifies the common blocks or symbols that must
be private for each process that runs a parallel DO-loop.
See Section 10.2.5.
CPAR$ PRIVATE_ALL

The CP AR$ PRIVATE_ALL directive forces all common blocks and symbols to
have PRIVATE defaults in routines compiled with the / PARALLEL qualifier.
See Section 10.2.6.
CPAR$ SHARED / [cb]/ (,/[cb]/] ...

is the name of a common block.

The CPAR$ SHARED directive specifies the common blocks to be shared by each
process that runs a parallel DO-loop.
See Section 10.2.7.
CP AR$ SHARED _ALL

The CPAR$ SHARED_ALL directive forces all common blocks to have SHARED
defaults in routines compiled with the /PARALLEL qualifier.
See Section 10.2.8.

0-6

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
DAT A nlist/clist/[[,] nlist/clist/] ...
nlist

is a list of one or more variable names, array names, array element
names, character substring names, or implied-DO lists, separated by
commas. Subscript expressions and substring expressions must be
constants.

dist

is a list of one or more constants separated by commas, each
optionally preceded by j•, where j is a nonzero, unsigned integer
constant.

The DATA statement initially stores elements of dist in the corresponding
elements of nlist.
See Section 4.3.

Data Type Declaration
See Type Declaration.

DECODE (c,f,b(,ERR=s][,IOSTAT=ios]) (list]
c

is an integer expression representing the number of characters to be
translated to interna l form .

is a fo rm at identifier.

is a scalar reference or array name reference that contains the
cha racters to be translated to internal form.

is the label of an executable statement.

ios

is an integer scalar memory reference that is defined as a positive
integer if an error occurs or as a zero if no error occurs.

list

is an 1/ 0 list.

The DECODE statement reads c characters from buffer b and assigns values to
the elements in list, converted according to format specification f.
See Section A.1.

DEFINE FILE u(m,n,U,v)[,u(m,n,U,v)]...
u

is a logical unit specifier.

specifies the n umber of records in th e file .

specifies the length of each record in 16-bit words.

specifies unformatted .

is an integer variable name.

VAX FORTRAN Language Summary

D-7

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary

The DEFINE FILE statement defines the record structure of a direct access file
where u is th e logical unit number, m is the number of fixed-length records in
the file, n is the length in 16-bit words of a single record, U is a fixed argument,
and v is the associated variable.
See Section A. 2.
DELETE((UNIT=]u(,REC=r](,ERR=s](,IOSTAT=ios])
D ELETE (u'r(,ERR=s](,IOST AT=ios])
u

is a logical unit specifier.

is a record specifier.

is the label of an executable statement.

ios

is an I/O status specifier.

The DELETE statement deletes records fro m relative or indexed files .
See Section 9. 7.
DICTIONARY 'cdd-path(/(NO)LIST) '

cdd-path is the full or relative pathname of a CDD object.
[NO]LIST

directs the compiler to include or not include the generated
FORTRAN source code in the listing.

The DICTIONARY statement extracts a data definition from the VAX/VMS
Common Data Dictionary, translates it to FORTRAN source code, and includes it
in a FORTRAN source program.
See Section 1.4.1.
DIMENSION a(d)(,a(d)) ...

a(d)

is an array declarator.

is an array name.

is the lower (optional) and upper bounds of the array. It takes the
form [dl:]du where dl is the lower bound and du is the upper bound.

The DIMENSION statement specifies storage space requirements for arrays.
See Section 4.5.
DO {s[,]] v=el,e2(,e3)

D-8

is the label of an executable statement. VAX FORTRAN allows the
statement label to be omitted.

is a variable name.

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
el

is a numeric expression that specifies the initial value of v.

is a numeric expression that specifies the terminal value of the
control variable.

is a numeric expression that specifies the value by which to increment the control variable.

The DO statement executes the DO loop by performing the following steps:

Evaluates cnt = INT((e2-el+e3)/e3).

Sets v = el.

If cnt is less than or equal to zero, does not execute the loop.

If cnt is greater than zero:

a.
b.

Executes the statements in the body of the loop.

Decrements the loop count (cnt = cnt-1). If cnt is greater
than zero, repeats the loop.

Evaluates v = v + e3.

See Section 5.3.

DO [s[,]) WHILE (e)
s

is the label of an executable statement. VAX FORTRAN allows the
statement label to be omitted.

is a logical expression .

The DO WHILE statement is similar to the DO statement, but DO WHILE
executes as long as the logical expression contained in the statement continues to
be true, instead of for a specified number of iterations.
See Section 5.3.2 .

ELSE
The ELSE statement defines a block of statements to be executed if logical
expressions in previous IF THEN and ELSE IF THEN statements have values of
false . See IF THEN.
See Section 5.7.3.

ELSE IF (e) THEN
e

is a logical expression.

VAX FORTRAN Language Summary

0-9

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
The ELSE IF THEN statement defines a block of statements to be executed if
logical expressions in previous IF THEN and ELSE IF THEN statements have
values of false, and the logical expression e has a value of true. See IF THEN.
See Section 5.7.3 .

ENCODE (c,f,b[,ERR=s)[,IOST AT=ios]) [list]
c

is an integer expression representing the number of characters
(bytes) to be translated to character form.

is a format identifier.

is a scalar reference or array name reference.

is a label of an executable statement.

lOS

is an integer scalar memory reference that is defined as a positive
integer if an error occurs or as a zero if no error occurs.

list

is an 1/0 list.

The ENCODE statement writes c characters into buffer b, which contains the
values of the elements of the list, converted according to format specification f.
See Section A.1.

END
The END statement marks the end of a program unit.
See Section 5.5.

END DO
The END DO statement marks the end of the body of a DO loop, and may be
used in place of a labeled statement.
See Section 5.4.

END IF
The END IF statement marks the end of a block IF construct.
See Section 5.7.3 .

END MAP
The END MAP statement marks the end of a field declaration or a series of field
declarations in a UNION .
See Section 4.15 .3.

END STRUCTURE

0-1 0 VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
The END STRUCTURE statement marks the end of a structure declaration .
See Section 4 .15 .1.
END UNION
The END UNION statement marks the end of a union declaration.
See Section 4.15 .3.
ENDFILE ([UNIT=]u[,ERR=s](,IOSTAT=ios])
ENDFILE u
u

is a logical unit specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

The ENDFILE statement writes an end-of-file record on logical unit u.
See Section 9.6.
ENTRY nam[([p[,p] ... ])]
nam

is a subprogram name.

is a dummy argument or an alternate return specifier ( • ).

The ENTRY statement defines an alternate entry point within a subroutine or
function subprogram.
See Section 6.2.4.
EQUIV ALEN CE (nlist)[,(nlist)] ...
nlist

is a list of two or more variable names, array names, array element names, or character substring names separated by commas.
Subscript expressions and substring expressions must be compiletime constant expressions. Records and record field s cannot be
specified in EQUIVALENCE statements.

The EQUIVALENCE statement assigns the same storage location to each of the
names in nlist.
See Section 4.6.
EXTERNAL v[,v] ...
EXTERNAL *v[•v] ...
v
...

is a subprogram name.
is used only if / NO F77 is specified .

VAX FORTRAN Language Summary

0-11

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
The EXTERNAL statement defines the names specified as user-defined subprograms.
See Sections 4.7 and A.6.

FIND ([UNIT=]u,REC=r[,ERR=s][,IOST AT=ios])
FIND (u'r[,ERR=s][,IOSTAT=ios])
u

is a logical unit specifier.

is a direct access record number.

is a label of an executable statement.

lOS

is an I/O status specifier.

The FIND statement positions the file on logical unit u to record r and sets the
associated variable to record number r.
See Section A.3 .

FORMAT (format-spec[, ... ])
formatspec

is a list of field descriptors and field separators.

The FORMAT statement describes the format in which one or more records are to
be transmitted; a statement label must be specified on the FORMAT statement.
See Chapter 8.

[typ] FUNCTION nam[* m][([p[,p) ... )))
typ

is a data type specifier.

nam

is a function name.

is a data type length specifier.

is a dummy argument.

The FUNCTION statement begins a function subprogram, indicating the program
name and any dummy argument names (p). An optional type specification can be
included.
See Section 6.2 .2.

GO TO s
s

is a label of an executable statement.

This GO TO statement transfers control to statement number s.
See Section 5.6.1.

D- 12

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
GO TO (slist)[,] e
slist

is a list of one or more statement labels separated by commas.

is an integer expression .

This GO TO statement transfers control to the statement specified by the value of
e (if e=l, control transfers to the first statement label; if e=2, control transfers to
the second statement label, and so forth). If e is less than one or greater than the
number of statement labels present, no transfer takes place.
See Section 5.6.2.

GO TO v[[,](slist)]
v

is an integer variable name.

slist

is a list of one or more statement labels separated by commas.

This GO TO statement transfers control to the statement most recently associated
with v by an ASSIGN statement.
See Section 5.6.3.

IF (e) sl,s2,s3
e

is an expression.

sl,s2,s3

are labels of executable statements.

This IF statement transfers control to statement sl, s2, or s3 depending on the
value of e (if e is less than zero, control transfers to sl; if e equals zero, control
transfers to s2; if e is greater than zero, control transfers to s3) .
See Section 5.7.1.

IF (e) st
e

is an expression.

is any executable statement except a DO, END DO, END, block IF,
or logical IF.

This IF statement executes the statement if the logical expression has a value of
true.
See Section 5.7.2.

VAX FORTRAN Language Summary

D-13

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
IF e1 THEN
block

ELSE IF e2 THEN
block

ELSE
block

END IF
el,e2

are logical expressions.

block

is a series of zero or more FORTRAN statements.

This IF statement defines blocks of statements and conditionally executes them.
If the logical expression in the IF THEN statement has a value of true, the first
block is executed and control transfers to the first executable statement after the
END IF statement.

If the logical expression has a value of false, the process is repeated for the next
ELSE IF THEN statement. If all logical expressions have values of false, the
ELSE block is executed. If there is no ELSE block, control transfers to the next
executable statement following END IF.
See Section 5.7.3.
IMP LI CIT typ(a[,a ]... )[, typ(a[,a ]... )]...
IMPLICIT NONE

typ

is a data type specifier.

is either a single letter, or two letters in alphabetical order, separated
by a hyphen (for example, X-Y).

NONE

inhibits the implicit type declaration of variables in the module.

The IMPLICIT statement implicitly declares the data types of variables within
program units. The element a represents a single letter or a range of letters
whose presence as the initial letter of a variable specifies the variable to be of that
data type.
IMPLICIT NONE and IMPLICIT must not be used in the same program unit.
See Section 4.8.
INCLUDE 'file-spec[/[NO]LIST] '
INCLUDE '[file-spec](module-name)[/[NO]LIST] '

file-spec

0- 14

is a character constant that specifies the file to be included.

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
mod ulename

is the name of a text m odule located in a text library.

/ [NO)LIST

indicates that th e statem ents in the specifi ed fil e are to be in
the source listing.

The INCLUDE statement includes the source state ments in the compilation from
the file or module specified .
See Section 1.4.2.

INQUIRE (par(,par] ... )
par

is a keyword specification having the form :
key = value

key

is a keyword (see th e list of keywords and values tha t
follo ws).

value

d epends on the keyword.

Keyword

Values

Inputs
FILE

fin

UNIT

DEFAULTFI LE

fin

Outputs
ACCESS

BLANK

CARRIAGECONTROL

DIRECT

ERR

VAX FORTRAN Language Summary

D-1 5

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary

Keyword

Values

Outputs (continued)
EXIST

FORM

FORMATTED

IOS TAT

KEYED

NAME

NAMED

NEXTREC

NUMBER

OPENED

ORGANIZATION

RECL

RECORDTYPE

SEQUENTIAL

UNFORMATTED

is a numeric expression identifying a logical unit.

fin

is a character expression identifying a file.

is an integer scalar memory reference.

is a logical scalar memory reference.

is a character scalar memory reference.

is a statement label.

The INQUIRE statement furnishes information on specified characteristics of a file
or of a logical unit on which a file might be opened.
See Section 9.3.

D-16

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
INTRINSIC v[,v] ...
v

is an intrinsic function name.

The INTRINSIC statement identifies symbolic names as representing intrinsic
functions and allows those names to be used as actual arguments.
See Section 4.9.

Map Declaration
See Union Declaration.

NAMELIST /group-name/ namelist[[,] /group-name/ namelist] ...
groupname

is a symbolic name.

name list

is a list of variables or array names, separated by commas, that is
associated with the preceding group-name.

The NAMELIST statement defines a list of variables or array names and associates
that list of names with a unique group-name for use in namelist-directed I/ O
statements.
See Section 4.10.

OPEN (par[,par] ... )
par

is a keyword specification in one of the following forms:
keyword
keyword = value

keyword

is a keyword (see the list of keywords and values that
follows) .

value

depends on the keyword.

VAX FORTRAN Language Summary

0-17

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary

D-18

Keyword

Values

ACCESS

'SEQUENTIAL'
'DIRECT'
'KEYED '
'APPEND '

ASSO CIATEVARIABLE

BLANK

'NULL'
'ZERO'

BLOCKSIZE

BUFFERCOUNT

CARRIAGECON TRO L

'FORTRAN '
' LIST'
' NONE '

DEFAULTFILE

DISP

(same as D ISPO SE)

DISPOSE

'KEE P ' or 'SAVE'
'DE LETE '
'PRINT '
'SU BMIT'
'SU BMIT /DELETE'
'PRINT / DELETE '

ERR

EXTEND SIZE

FILE

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary

Keyword

Values

FORM

'FORMATTED'
'UNFORMATTED'

INITIALS IZ E

IOS TAT

KEY

keys pee

MAXREC

NAME

(same as FILE)

NOSP AN BLOCKS
ORGANIZATIO N

'SEQ UENTIA L'
' RELATIVE'
'INDEXED '

READO NLY
RECL

RECORDSIZE

(same as RECL)

REC ORDTYPE

'FIXED'
'VARIABLE '
'SEGMENTED '
'STREAM'
'STREAM_CR'
'STREAM_LF'

SH ARED
STATUS

'OLD'
'NEW'
'SCRATCH'
'UNKNOWN'

TYPE

(same as STATUS)

UNIT

USER OPEN

VAX FORTRAN Language Summary D-19

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
c

is a character scalar reference, numeric scalar memory
reference, or numeric array name reference .

is a numeric expression.

is a program unit name.

is a statement label.

is an integer scalar memory reference.

keyspec is e l:e2[:dt[ :dr]].
e1

is first byte position of the key .

is last byte position of the key.

is the d ata type, INTEGER or CHARACTER.

is the direction of the key, ASCENDIN G or DESCENDING .

The OPEN statement opens a fil e on the specified logical unit according to the
parameters specified by the keywords .
See Section 9 .1.
OPTIONS qualifier[qualifier ...]
qualifi er

is one of the fo llowing:
/ NOCHECK
ALL
}
([NO]OVE RFLOW, [NO]BOUNDS, [NO]UNDERFLOW)
{ NONE
/ [NO]EXTEND_ SOURCE
/ [NO]F77
/ [NO]G _ FLOATING
/[NO]I4
/ CHECK=

The OPTIONS statemen t overrides the command line qualifie rs fo r a single
program unit.
See Section 1.4 .3.
PARAMETER (p=c[,p=c] ... )
p

D-20

is a symbolic name.

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
c

is a constant, the name of a constant, or compile-time constant
expression .

The PARAMETER statement defines a symbolic name for a constant.
See Sections 4.11 and A.4 .

PAUSE (disp)
disp

is a decimal digit string containing 1 to 5 digits or a character
constant.

The PAUSE statement displays a message on the screen and temporarily suspends
program execution in order to permit you to take some action. You can respond
by typing CONTINUE, EXIT, or DEBUG .
See Section 5.8 .

PRINT
See WRITE statements (sequential access).
See Section 7.6.

PROGRAM nam
nam

is a program name.

The PROGRAM statement specifies a name for the main program.
See Section 4.12 .

Read Statements-Formatted Sequential Access
READ ((UNIT=)u,(FMT=]f(,ERR=s](,IOST AT=ios](,END=s]) (list]
READ f(,list]
ACCEPT f[,list]
u

is a logical unit specifier.

is the nonkeyword form of a format specifier.

is a label of an executable statement.

IOS

is an 1/0 status specifier.

list

is an 1/0 list.

These input statements read one or more logical records from unit u and assign
values to the elements in the list. The records are converted according to the
format specifier (f).
See Section 7.2.1.1 and 7.5.

Read Statements-List-Directed Sequential Access

VAX FORTRAN Language Summary

D-21

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
READ ([UNIT=]u,[FMT=]•[,ERR=s][,IOSTAT=ios][,END=s]) [list]
READ *[,list]
ACCEPT •[,list]
is a logical unit specifier.
u
...

denotes list-directed formatting .

is a label of an executable statement.

ios

is an 1/0 status specifier.

list

is an IjO list.

These input statements read one or more logical records from unit u and assign
values to the elements in the list. The records are converted according to the data
type of the list element.
See Section 7.2.1.2 and 7.5 .

Read Statements-Namelist-Directed Sequential Access
READ ([UNIT=]u,[NML=]nl[,ERR=s)[,IOST AT=ios)[,END=s])
READ nl
ACCEPT nl
u

is a logical unit speci fier.

is a nam elist group -name.

is a label of an executable statement.

ios

is an I/ O status specifier.

These in put statements read one or m ore logical records from unit u and assign
values to specified namelist entities. The records are converted according to the
data type of the namelist en tities .
See Sections 7.2.1.3 and 7.5.

Read Statements-Unformatted Sequential Access
READ ([UNIT=]u[,ERR=s][,IOST AT=ios][,END=s]) [list]
u

is a logical unit specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

This READ statement reads one unformatted record from unit u and assigns
values to the elements in the list.

0-22 VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
See Section 7.2.1.4.
Read Statements-Formatted Direct Access
READ ([UNIT=]u,[FMT=]f,REC=r[,ERR=s][,IOSTAT=ios]) [list]
READ (u 'r,(FMT=)f(,ERR=sJl,IOST AT=iosj) [list]
u

is a logical unit specifier.

is a record specifier.

is a format specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

This READ statement reads record r from unit u and assigns values to the
elements in the list. The record is converted according to f.
See Section 7.2.2.1.
Read Statements-Unformatted Direct Access
READ ([UNIT=]u,REC=r[,ERR=s][,IOSTAT=ios]) [list]
RE AD (u 'r(,ERR=s][,IOSTAT=ios)) [list]
u

is a logical unit specifier.

is a record specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

This READ statement reads record r from unit u and assigns values to the
elements in the list.
See Section 7.2.2.2.
Read Statements-Formatted In dexed and Unformatted Indexed
Formatted indexed READ statement:
READ ((UNIT=]u,(FMT=)f,keysp ec(,KEYID=kn ](,ERR=s] (,IOSTAT=ios]) (list]
Unformatted indexed READ statement:
READ ((UNIT=)u,keyspec(,KEYID=kn][,ERR=s] (,IOSTAT=ios]) (list]
u

is a logical unit specifier.

VAX FORTRAN language Summary

D-23

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
f

is a fo rmat specifi er.

keyspec

is a key specifier (see. Section 7.1.1.6).

is a key-of-reference specifier.

is the label of an executable statement.

ios

is an I/ O status specifi er.

list

is an I/ O list.

These input statements read one or more logical records specifi ed by key value,
and assign values to the elements in th e list.
See Sections 7.2.3.1 and 7.2. 3.2.

Read Statements-Formatted Internal and List-Directed Internal
Formatted internal READ statement:

READ (intu, fmt [,iostat][,err][,end]) [iolist]
List-directed internal READ statement:

READ (intu,*[,iostat][,err][,end]) [iolist]
in tu

is an internal file specifier.

fmt

is a format specifier.

is a list-directed formatting specifier.

iostat

is an I/O status specifier.

err, end

are transfer-of control specifiers.

iolist

is the 1/0 list specifier.

These input statements read into elements in the list. They read one or more
internal records containing character strings, converting in accordance with the
format specification.
See Section 7.2.4.

RECORD /structure-name/ record-namelist
[,/structure-name /record-namelist]

[,/structure-name/ record-name list]
structurename

is the name of a previously declared structure.

D-24 VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary

recordnamelist

is one or more variable or array names, or both; separated by
commas .

The RECORD statement creates a record for each variable specified or an array
of records for each arra y specified . The structure declaration identifi ed by
structure-name defines the form of these records.
See Section 4.13 .
RETURN [i]

is an integer value that indicates which alternate return is to be
taken.
The RETURN statement returns control to the calling program from the current
subprogram.
See Section 5. 9.
REWIND ([UNIT=]u[,ERR=s][,IOSTAT=ios])
REWIND u
u

is a logical unit specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

The REWIND statement repositions logical unit u to the beginning of the currently
opened file.
See Section 9 .4.
REWRITE Statement-Formatted Indexed and Unformatted Indexed

Formatted indexed REWRITE statement:
REWRITE ((UNIT=]u,(FMT=]f(,E RR=s][,IOSTAT=ios]) (list]

Unformatted indexed REWRITE statement:
REWRITE ((UNIT=]u[,ERR=s][,IOST AT=ios]) (list]
u

is a logical unit specifier.

is a format specifier.

is a label of an executable statem ent.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

The REWRITE statement transfers data from internal storage to the current record
in an indexed file .

VAX FORTRAN language Summary

D-25

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
See Section 7.4 .

SA VE [a[,a] ... )
a

is the name of a variable, an array, or a named common block
enclosed in slashes.

The SAVE statement retains the definition status of an entity after the execution
of a RETURN or END statement in a subprogram.
See Section 4 .14.

Statement Function

f([p(,p )... )) = e
f

is a statement function name.

is a dummy argument.

is an expression.

A statement function creates a user-defined function having the variables p as
dummy arguments. When referred to, the expression is evaluated using the actual
arguments in the function call.
See Section 6.2.1.

STOP [disp]
disp

is a decimal digit string containing 1 to 5 digits or a character
constant.

The STOP statement terminates program execution and prints the display, if one
is specified.
See Section 5 .10.

Structure Declaration Block
STRUCTURE [/structure-name/] [field-namelist]
field-declaration
[field-declaration]

[field-declaration]
END STRUCTURE
structurenam e

0-26

is th e name tha t is used in RECOR D sta tements to refer to a
stru cture.

VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
field nameli st

are uniqu e fi eld names. (Used only in nested structure declarations.)

field declaration

is any decl aration or combination of declarations of substructures,
unions, or typed data .

A stru cture declaration bl ock defin es th e field names, types of data wi thin fi elds,
and the order and alignment of fields within a record . Unlike type declaration
statements, structure declarations do not create variables . Structured variables
(records) are created when you use a RECO RD statement containing the name of
a previously declared stru cture.
See Section 4.15 .1.

SUBROUTINE nam[([p[,p] ... ])]
nam

is a subroutine name .

is a dummy argument or an alternate return specifier ( * ).

The SUBROUTINE statement begins a subroutine subprogram, indicating the
program name and any dummy argument names (p).
See Section 6.2.3 .

TYPE
See WRITE statements (sequential access).
See Section 7.6.

Type Declarations-Character and Numeric
Typ e Declaration (Character):
CHARACTER[ •len[,]] v[ •len}/clist/] [,v[ •lenl /clist/} ...
len

specifies the length of the character data elements; or it can be an
asterisk enclosed in parentheses.

is a variable name, arra y name, function or function entry name,
or an array declarator. The name can optionally be followed by a
length specifier (*n) .

dist

is an initial va lue or values to be assigned to the immediately
preceding variable or array element.

The character type declaration assigns the specified data type to the symbolic
names (v).
See Section 4.4.2.

Typ e Declaration (Num eric):

VAX FORTRAN Language Summary

D-27

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
type [*n ]v[*n ][dist][, v[*n ][/ dist/]]
type

is one of the following data type specifiers: BYTE, LOGICAL,
INTEGER, REAL, DOUBLE PRECISION, COMPLEX, or DOU BLE
COMPLEX.

is an in teger that specifies the byte length of v. It m ust be an
acceptable length fo r the entity (see Table 2- 1); *n is not valid for
DO UBLE P RECISIO N and DOU BLE COM PLEX da ta types.

is a variable name, array name, function or function entry name, or
an array declarator.

clist

is an in itial value or val ues to be assigned to the immediately
preceding variable or array element.

The Numeric Type Declaration assigns the specified data type to the symbolic
names (v).
See Section 4.4.1.

Union Declaration
UNIO N

map-declaration
map-declaration
[map-declaration]

[map-declaration]
END UNIO N
w here map-declaration is:
MAP

fi eld-declaration
[field-declaration]

[field-declaration)
END MAP
fielddeclaration

is any declaration or combination of declarations of substructures,
union s, or typed data.

Unions define a data area that can be shared by fields or groups of fields at run
time .

D-28 VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
See Section 4 .15 .3.

UNLOCK ([UNIT=)u[,ERR=s)[,IOST AT=ios])
UNLOCK u
u

is a logical unit specifier.

is a label of an executable statement.

ios

is an I/ O sta tus specifier.

The UNLOCK statement frees a previously locked record in the file connected to
logical unit u.
See Section 9.8.

VIRTUAL a(d)(,a(d))...
a(d)

is an array declarator.

is an array name.

is the lower (optional) and upper bounds of the array. It takes the
fo rm [dl:)du w here dl is the lower bound and du is the upper bound.

The VIRTUAL statement has the same effect as the DIMENSION statement and
is included for compatibility with PDP-11 FORTRAN.
See Section 4.5.

VOLATILE nlist
nlist

is a list of one or more variable names, array names, or common
block names separated by commas .

The VOLATILE statement prevents all optimizations for the items specified in the
name list.
See Section 4 .16.

Write Statements-Formatted Sequential Access
WRITE ([UNIT=)u,[FMT=)f(,ERR=s)[,IOST AT=ios]) [list)
PRINT £[,list]
TYPE £[,list)
u

is a logical unit specifier.

is a format specifier.

is a label of an executable statement.

ios

is an I/O status specifier.

list

is an 1/0 list.

VAX FORTRAN Language Summary

D-29

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
These output statements write one or more logical records to unit u containing
the values of the elements in the list. The records are converted according to f.
For information about the formatted sequential access WRITE statement, see
Section 7.3 .1.1. For information about formatted sequential access PRINT and
TYPE statements, see Section 7.6.

Write Statements-List-Directed Sequential Access
WRITE ([UNIT=]u,[FMT=]•[,ERR=s][,IOSTAT=ios]) [list]
PRINT •[,list]
TYPE *[,list]
u

is a logical unit specifier.
denotes list-directed formatting.

is a label of an executable statement.

ios

is an I/O status specifier.

list

is an I/O list.

These output statements write one or more logical records to unit u containing
the values of the elements in the list. The records are converted according to the
data type of the list element.
For information about the list-directed sequential access WRITE statement, see
Section 7.3.1.2. For information about list-directed sequential access PRINT and
TYPE statements, see Section 7.6.

Write Statements-Namelist-Directed Sequential Access
WRITE ([UNIT=)u,[NML=)nl[,ERR=s) [,IOST AT=ios])
PRINT nl
TYPE nl
u

is a logical unit specifier.

is a namelist group -n ame.

is a label of an executable statement .

ios

is an I/ O status specifier.

These output statements wri te one or more logical records to unit u containing
th e values of the namelist entities . The records are converted according to th e
data type of the nam elist entities.
For information about the nam elist-directed sequential access WRITE statement,
see Section 7.3. 1. 3. For in fo rm ation about namelist-directed sequential access
PRINT and TYPE statemen ts, see Section 7.6.

0-30 VAX FORTRAN Language Summary

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
Write Statements-Unformatted Sequential Access
WRITE ([UNIT=]u[,ERR=s](,IOST AT=ios]) [list]
u

is a logical unit specifier.

is a label of an executable statement label.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

This WRITE statement writes one unformatted record to unit u containing the
values of the elements in the list.
See Section 7.3.1.4.
Write Statements-Formatted Direct Access
WRITE (JUNIT=lu,JFMT=lf,REC=r[,ERR=s1[,IOST AT=ios]) [list]
WRITE (u 'r,f[,ERR=s][,IOST AT=ios]) [list
u

is a logical unit specifier.

is a record specifier.

is a format specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

These WRITE statements write the values of the elements of the list to record r
on unit u. The record is converted according to f.
See Section 7.3.2 .1
Write Statements-Unformatted Direct Access
WRITF ([UNTT=lu,REC=rJ,ERR=s)[,IOSTAT=ios]) [list]
WRITE (u 'r[,ERR=s)[,IOST AT=ios]) [list]
u

is a logical unit specifier.

is a record specifier.

is a label of an executable statement.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

These WRITE statements write record r to unit u containing the values of the
elements in the list.

VAX FORTRAN Language Summary

0-J 1

Table D-2 (Cont.):

VAX FORTRAN Language

Statement Summary
See Section 7.3.2.2.

Write Statements-Formatted Internal and List-Directed Internal
Formatted internal WRITE statement:

WRITE (intu,[FMT=]f(,ERR=s)[,IOSTAT=ios]) (list]
List-directed in ternal WRITE statement:

WRITE (intu,(FMT=]*(,ERR=s] (,IOST AT=ios]) (list]
intu

is an internal file specifier.

•

denotes list-directed formatting.

is a format specifier.

is the label of an executable statement.

ios

is an 1/0 status specifier.

list

is an 1/0 list.

These WRITE statements write elements in the list to the internal file specified by
intu. The formatted internal WRITE statement converts the elements to character
strings in accordance with the format specification.
See Section 7.3.4.

D.3 Library Functions
Table D-3 lists the VAX FORTRAN intrinsic functions. Superscripts in the
table refer to the notes that follow the table. Refer to Section 6.3 for more
information about intrinsic functions. For descriptions of the intrinsic
function algorithms, refer to the VMS RTL Mathematics (MTH$) Manual.

0-32 VAX FORTRAN Language Summary

Table D-3:

VAX FORTRAN Intrinsic Functions
No. of
Generic
Name
Arguments

Functions
1

Specific
Name

Type of
Argument

Type of
Result

SQRT

SQRT
OSQRT
Q SQRT
CSQRT
COSQ RT

REAL•4
REAL•8
REAL• 16
COMPLEX•8
COMPLEX•1 6

REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•16

Natural Logarithm 2
loge a

LOG

ALOG
OLOG
Q LOG
CLOG
CO LOG

REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•1 6

REAL•4
REAL•8
REA L•16
COMPLEX•8
COM P LEX•16

Common Logarithm 2
log10a

LOG IO

A LOG IO
OLOGIO
QLOGIO

REAL•4
REAL•8
REAL•1 6

REAL•4
REAL•8
REAL•16

Exponential
ea

EXP

EXP
OEXP
Q EXP
CEXP
CO EXP

REAL•4
REAL•8
REAL*l 6
COMPLEX•8
C OMPLEX• 16

REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•16

Sine 3

SIN

SIN
OSIN
QSI N
CSIN
COS IN

REAL•4
REAL*8
REAL•16
COMPLEX•8
C OMP LEX•16

REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX*16

S INO

SINO
OSI NO
QSINO

REAL• 4
REAL• 8
REAL•l 6

REAL•4
REAL*8
REAL•16

Square Root
a 1;2

Sin a

Sine 3 (d egree)
Sin a

The argument of SQRT, DSQRT, or QSQRT must be greater than or equal to zero. The result of CSQRT or
CDSQRT is the principal value, with the real part greater than or equal to zero . When the real part is zero,
the result is the principal value, with the imaginary part greater than or equal to zero.
2

The argument of ALOG, DLOG, QSQRT, ALOGlO, DLOGlO, QLOG lO , ATA ND, ATAN2D, AS IND,
DAS IND, ACOSD, DACOSD, or QACOSD must be greater than zero. The argument of CLOG or CDLOG
must not be (0.,0.).
3

The argument of SIN, DSIN, QSIN COS, DCOS, QCOS, TAN, DTAN, or QTAN must be in radians. The
argument is treated modulo 2•pi. The argument of SIND, COSD, or TAND mu st be in degrees . The argument
is trea ted modu lo 360 .

VAX FORTRAN Language Summary

D-33

Table D-3 (Cont.):
Functions
Cosine 3
Cos a

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name
1

cos

Specific
Name

Type of
Argument

Type of
Result

cos
CDC O S

REAL•4
REAL•8
REAL• 16
COMPLEX•8
COMPLEX•16

REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•16

DCOS
QCOS

ccos

Cosine 3 (degree)
Cos a

COSD

COSD
DCOSD
QCOSD

REAL•4
REAL•8
REAL•16

Tangent 3
Tan a

TAN

TAN
DTAN
QTAN

REAL•4
REAL•8
REAL• l 6

REAL•4
REAL•8
REAL•16

Tangen t 3 (degree)
Tan a

TAND

TAND
DTAND
QT AND

REAL•4
REA L• 8
REAL•16

REAL•4
REAL•8
REAL•16

Arc Sine 4 •5
Arc Sin a

ASIN

ASIN
DAS IN
QASIN

REAL•4
REAL•8
REAL•16

Arc Sine (degree)
Arc Sin a

AS IND

AS IND
DASI ND
QASIND

REAL•4
REAL•8
REAL•1 6

REAL• 4
REAL•8
REAL• 16

Arc Cosine 4 ' 5
Arc Cos a

ACOS

ACOS
DACOS
QACOS

REAL•4
REAL•8
REAL•1 6

REAL•4
REAL•8
REAL• 16

Arc Cosine (d egree)
Arc Cos a

ACO SD

ACOSD
DACOSD
QACOSD

REAL• 4
REA L•8
REAL•1 6

REAL•4
REAL•8
REA L•16

The argument of SIN, DSIN , QSIN, COS, DCOS, QCOS, TAN, DTAN, or QTAN must be in radians. The
argument is treated modulo 2•pi. The argumen t of SIN O, COSD, or TAN D m ust be in degrees. The argum ent
is treated modulo 360 .
4

The absolute value of the argument of ASIN, DASIN, Q AS IN, ACOS, DACOS, Q ACOS, ASIN D, DASIND,
QASIND, ACOSD, DACOSD, or QAC OSD must be less than or equal to 1.
5

The result of ASIN, DASIN, QASIN , ACOS, DACOS, QACOS, ATAN, DATAN, QATAN, ATAN2, DATAN2,
or QATAN 2 is in radians. The resul t of ASI ND, DAS !ND, QASIN D, ACOS D, DAC OSD, QACOSD, ATAND,
DATAND, QATAND, ATAN 20, DATA N 20, or Q ATAN 20 is in degrees.

D-34

VAX FORTRAN Language Summary

Table D-3 (Cont.):

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

Arc Tangent 5
Arc Tan a

ATAN

ATAN
DATAN
QATAN

REAL•4
REAL•8
REAL•16

REAL•4
REAL•8
REAL•l6

Arc Tangent 5 •7 (degree)
Arc Tan a

ATAND

Arc Tangent 5 •6
Arc Tan aif a2

ATAN2

ATAND
DATAN D
Q ATAND
ATAN2
DATAN2
Q ATAN2

REAL•4
REAL•8
REAL• 16
REAL•4
REAL•8
REAL•16

REAL•4
REAL•8
REAL•16
REAL•4
REAL•8
REAL•16

Arc Tangent 5 •7 (degree)
Arc Tan aif a 2

ATAN 2D

ATAN2D
DATAN2 0
Q ATAN2D

REAL•4
REAL•8
REAL•16

Hyperbolic Sine
Sinha

SINH

SINH
DSINH
QSI N H

REAL•4
REAL•8
REAL•16

Hyperbolic Cosine
Cosh a

COSH

COSH
DCOSH
QCOSH

REAL•4
REAL•8
REAL•16

Hyperbolic Tangent
Tanh a

TANH

TANH
DTANH
QTANH

REAL•4
REAL•8
REAL•16

Functions

The result of ASIN, DASIN, QAS IN, ACOS. DACOS. QACOS, ATAN. DATAN. QATAN , ATAN2, DATAN2,
or QATAN2 is in radians. The resu lt of ASIND, DASIND, QASIND, ACOSD, DACOSD, QACOSD, ATAND,
DATAND, QATAND, ATAN 2D, DATAN2D, or QATAN2D is in degrees.

If the value of the first argument of ATAN2, DATAN2, or QATAN2 is positive, the result is positive. When
the value of the first argument is zero, the result is zero if the second argument is positive and pi if the
second argument is negative. If the value of the first argument is negative, the result is negative. If the value
of the second argument is zero, the absolute value of the result is pi/2 . Both arguments must not have the
value zero. The range of the result for ATAN2, DATAN2, and QATAN2 is: -pi < result < pi.
7

If th e value of the first argument of ATAN 2D, DATAN2 D, or QATAN2D is positive, the resu lt is positive.
When the value of th e first argument is zero, th e resu lt will be zero if the second argument is positive and
180 degrees if the second argument is nega ti ve. If th e value of the first argument is negative, the result is
negative. If th e valu e of th e second argu ment is zero, the absolute value of the result is 90 degrees. Both
arguments must not ha ve th e va lue zero. The range of the result for ATAN2D, DTAN2D, QATAN2D is: - 180
degrees < result < 180 degrees.

VAX FORTRAN Language Summary

0-35

Table D-3 (Cont.):
Functions
Absolute Value 8
lal

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

IIA BS
JI ABS
ABS
DABS
QABS
CABS
CDABS
IIABS
JIABS

INTEGER* 2
INTEGER*4
REAL•4
REAL•8
REAL*1 6
COMPLEX•8
COMPLEX* l6
INTEGER*2
INTEGER*4

INTEGER*2
INTEGER*4
REAL•4
REAL•S
REAL•16
REAL•4
REAL•8
INTEGER*2
INTEGER•4

INT

IIN T
}INT
II DINT
JI DINT
IIQINT
JIQINT

ID INT

IIDINT
JI DINT
IIQINT
TIO INT
AINI
DINT
QINT

REAT.*4
REAL•4
REAL*8
REAL*8
REAL* 16
REAL*l6
COMPLEX*8
COMPLEX•8
COMPLEX*l6
COMPLEX* 16
REAL*8
REAL•8
REAL*16
REAL*l6
REAL*4
REAL*8
REAL*16

INTEGER*2
INTEGER•4
INTEGER*2
INTEGER•4
INTEGER*2
INTEG ER*4
INTEGER* 2
INTEGER•4
INTEGER*2
INTEGER*4
INTEGER*2
INTEGER•4
INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL*1 6

ABS

IABS
Truncation 9 • 10
[a]

IQ INT
AINI

The absolute value of a complex number, (X,Y), is the real value SQRT (X**2 + Y**2)

[x] is defined as the largest integer whose magnitude does not exceed the magnitude of x and whose sign is
the same as that of x. For example, [5 .7] equals 5. and (-5 .7] equals -5 .
10

The functions INT, IDINT, IQ INT, NINT, IDNINT, IQN INT, !FIX, MAXI , MINI, and ZEXT return
INTEGER*4 values if the /14 command qualifier is in effect, INTEGE R*2 va lues if th e / NO l4 qua lifi er is
in effec t.

0-36

VAX FORTRAN Language Summary

Table D-3 (Cont.):
Functions
Nearest Integer9 • 10
[a+.S•sign(a)]

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

IN INT
JN INT
IIDNNT
JIDNNT
IIQNNT
JIQNNT
IIDNNT
JIDNNT
IIQN N T
JIQNNT
AN INT
DNINT
QNINT

REAL•4
REAL•4
REAL•8
REAL•S
REAL•16
REAL• 16
REAL•S
REAL•S
REAL• 16

INTEGE R•2
INTEGER•4
INTEGE R• 2
INTEGER•4
INTEGE R•2
INTEGE R• 4
INTEG ER• 2
INTEGER•4
IN TEGER•2

REAL•4
REAL•S
REAL•16

REAL•4
REAL•S
REAL• 16

IZEXT

LOGICAL• !
LO GICAL•2
LOGICAL•2
LOGICAL•!
LOGICAL•2
LOGICAL•4
INTEGER•2
INTEGER•4

IN TEGE R• 2

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•16

REAL•4
REAL•4
REAL•4
REAL•4
REAL• 4
REAL•4
REAL• 4

NINT

IDNINT
IQ N INT
AN INT

Zero-Extend Functions

ZEXT

JZEXT

Conversion to REAL•4 11

REAL

FLOATI
FLOATJ
SNGL
SNGLQ

INTEGER•4

[x] is defined as the largest integer whose magnitude does not exceed the magnitude of x and whose sign is
the same as that of x. For example, [5 .7] equals 5. and [-5 .7] equals -5 .
10

The functions INT, IDINT, IQINT, NINT, IDNINT, IQ NINT, IFIX, MAXI, MINI, and ZEXT return
INTEGER•4 values if the /I4 command qualifier is in effect, INTEGE R•2 va lues if th e / NO I4 qualifier is
in e ffect.
11

Functions that cause conversion of one data type to another type provide the same effect as the implied
conversion in assignment statements. The following functions return the value of the argument without
conversion: the function REAL with a real argument, the function DBLE with a double precision argument,
the function INT with an integer argument, and th e function QEXT with a REAL• 16 argumen t.

VAX FORTRAN Language Summary

D-37

Table D-3 (Cont.):

VAX FORTRAN Intrinsic Functions

Functions

No. of
Generic
Arguments Name

Conversion to REAL•8 11

Specific
Name

DBLE
DBLE
DBLEQ

Conversion to REAL•16 11

QEXT
QEXT
QEXTD

Type of
Argument

Type of
Result

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•16

REAL•8
REAL•8
REAL•8
REAL•8
REAL•8
REAL•8
REAL•8

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•16
COMPLEX•8
COMPLEX•16

REAL•16
REAL•16
REAL•16
REAL•16
REAL•16
REAL•16
REAL•16

Fix1 0, 11

IFIX

(REAL•4-tointeger
conversion)
Float 11

II FIX
JI FIX

REAL•4
REAL•4

INTEGER•2
INTEGER•4

FLOAT

(Integer-toREAL•4
conversion)
REAL•8 Float 11

FLO ATI
FLOAT}

INTEGER•2
INTEGER•4

REAL•4
REAL•4

DFLOAT

DFLOTI
DFLOTJ

INTEGER•2
INTEGER•4

REAL•8
REAL•8

INTEGER•2
INTEGER•4

REAL•16
REAL•16

(Integer-toREAL•8
conversion)
REAL•16 Float
(Integer-toREAL•16
conversion)

QFLOAT

The function s INT, !DINT, IQINT, NINT, IDNINT, IQNINT, IFIX, MAXI , MINI, and ZEXT return
INTEGER•4 values if the / I4 command qualifier is in effect, INTEGER• 2 va lues if th e / NOI4 qual ifier is
in effect.

11 Functions that cause conversion of one data type to another type provide the same effect as th e implied
conversion in assignment statements. The following fun ctions return the value of the argument without
conversion : the function REAL with a real argument, the function DBLE with a double precision argument,
the function INT with an integer argument, and th e function QEXT with a REAL• 16 argumen t.

D-38

VAX FORTRAN Language Summary

Table D-3 (Cont.):
Functions

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

Conversion to
COMPLEX*8,
or
COMPLEX*8 from Two
Arguments 12

1,2
1,2
1,2
1,2
1,2
1
1

CMPLX

INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL*16
COMPLEX*8
COMPLEX*16

COMPLEX*8
COMPLEX*8
COMPLEX*8
COMPLEX*8
COMPLEX*8
COMPLEX*8
COMPLEX*8

Con versi o n to
COMPLEX*1 6,
or
C O MPLEX*16 from Two
Arguments 12

1,2
1,2
1,2
1,2
1,2
1
1

DCMPLX

INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL*16
COMPLEX*8
COMPLEX*l6

COMPLEX*16
COMPLEX*16
COMPLEX*16
COMPLEX*16
COMPLEX*16
COMPLEX*l6
COMPLEX*16

Real Part of Complex

REAL
DREAL

COMPLEX*8
COMPLEX16

REAL*4
REAL*8

Imaginary Part of
Complex

AI MAG
DIM AG

COMPLEX*8
COMPLEX*l6

REAL*4
REAL*8

Complex from Two
Arguments

(See Conversion to COMPLEX*8 and
Conversion to COMPLEX*l6)

Complex Conjugate
(if a=(X,Y)
CONJG(a)=(X,-Y))

CONJG
DCONJG

COMPLEX*8
COMPLEX*16

REAL•8 product of
REAL•4s
a1 *a2

DP ROD

REAL*4

REAL*8

CONJG

12 When CMPLX and DCMPLX have only one argument, this argument is converted into the real part of a
complex value, and zero is assigned to the imaginary part. (When there are two arguments (not complex), a
complex value is produced by converting the first argument into the real part of the value and converting the
second argument into the imaginary part .)

VAX FORTRAN Language Summary

D-39

Table D-3 (Cont.):
Functions
Maximum 10
max(a1,a2, . . . an)

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

IMAXO
JMAXO
AMAXl
DMAXI
QMAXl
IMAXO
JM AXO
IMAXl
JM AXI
AIMAXO
AJMAXO

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•I6
INTEGER• 2
INTEGER•4
REAL•4
REAL•4
INTEGER•2
INTEGER•4

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•I6
INTEGER•2
INTEGER•4
INTEGER•2
INTEGER•4
REAL•4
REAL•4

IMINO
JMINO
AMINl
DMINI
QMINl
IMINO
JMINO
IMINl
JMINl
AIMINO
AJMINO

INTEGE R•2
INTEGER•4
REAL•4
REAL•8
REAL• 16
INTEGER•2
INTEGER•4
REAL•4
REAL•4
INTEGER• 2
INTEGER•4

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•16
INTEGER•2
INTEGER•4
INTEGER•2
INTEGER•4
REAL•4
REAL•4

IIDIM
JIDIM
DIM
DDIM
QDI M
II DIM
JIDIM

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL• 16
INTEGER•2
INTEGER•4

INTEGER•2
INTEGER•4
REAL•4
REAL•8
REAL•16
INTEGER•2
INTEGER•4

(returns the value
from among the
argument list;
there must be at
least two
arguments)

MAX

MAXO
MAXI
AMAXO

Minimum 10
min(a1 ,a2, .. . an)

(returns the
minimum value
from among
the argument
list; there
must be at
least two
arguments)
Positive Difference
a1-(min(a1,a 2))

MIN

MINO
MINI
AMINO
2

(returns the first
argument m inus
the minimum of
the two
arguments)

DIM

IDIM

10The function s INT, IDINT, IQ INT, NINT, IDNINT, IQ N INT, IFIX, MAXl , MINI, and ZEXT return
INTEGER•4 values if the / 14 command qualifier is in effe ct, INTEGER • 2 values if th e / NOI4 qua li fi er is
in e ffec t.

0-40

VAX FORTRAN Language Summary

Table D-3 (Cont.):
Functions
Remainder
a1-a 2*[a1 /a2]

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

MOD

!MOD
JMOD
AMOD
DMOD
QMOD

INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL* l 6

INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL*l6

SIGN

IISIGN
JISIGN
SIGN
DSIGN
QSIGN
IIS IGN
JI SIGN

INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL*l6
INTEGE R*2
INTEGER*4

INTEGER*2
INTEGER*4
REAL*4
REAL*8
REAL*16
INTEGER*2
INTEGER*4

(returns the
remainder when
the first
argument is
divided by
the second)
Transfer of Sign
la1 I Sign a 2

ISIGN
Bitwise AND
(performs a
logical AN D on
corresponding bits)

IAND

II AND
JI AND

INTEGER*2
INTEGER*4

Bitwise OR
(performs an
inclusive OR
on corresponding
bits)

IOR

IIOR
JIOR

INTEGER*2
INTEGER*4

Bitwise Exclusive OR
(performs an
exclusive OR
on corresp o nding
bits)

IEOR

IIEOR
JIEOR

INTEGER*2
INTEGER*4

Bitwise Complement
(complements
each
bit)

N OT

INOT
JNOT

INTEGER*2
INTEGER*4

Bitwise Shift
(a 1 logically
shifted
left a 2 bits)

IS H FT

IISH FT
JISHFT

INTEGER*2
INTEGER*4

VAX FORTRAN Language Summary

0-41

Table D-3 (Cont.):

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

Bit Extraction
(extracts bi ts a 2
thru a 2+ar 1 from
ai;
see also MVBITS
system subroutine)

IBITS

IIBITS
JIBlTS

INTEGER*2
INTEGER*4

INTEGER*4
INTEGER*4

Bit Set

IBSET

IIBSET
JIBS ET

INTEGER*2
INTEGER*4

Bit Test
(returns .T RUE. if
bit a 2 of argument
a1 e quals 1)

BTEST

BITE ST
BJTEST

INTEGER*2
INTEGER*4

LOGICAL*2
LOG IC AL*4

Bit Clear
(returns the value
of a 1 with bit
a2 of a 1
set to 0)

IBCLR

IIBCLR
JIBCLR

INTEGER*2
INTEGER*4

INTEGER*4
INTEGER*4

Bitwise Circular Shift
(circularly s h ifts
rightmost a 3 bits
of a rgument a 1 b y
a 2 places;
bits in a1
beyond the value
specified by a3
are unaffected)

ISH FTC

IISHFTC
JISHFTC

INTEGER*2
INTEGER*4

INTEGER*4
INTEGER*4

Length
(returns length of
the character
expression; see
Chapter 2 for
additional
information on
character
functions)

LEN

CHARACTER

INTEGER*4

Functions

(returns the value
of a 1 wi th
bit a 2 of ai
set to 1)

D-42

VAX FORTRAN Language Summary

Table D-3 (Cont.):

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

Index (C1 ,C2)
(return s the
position of the
substring c2 in
character
expression c 1 ;
see Chapter 2
for additional
information on
character
functions)

INDEX

CHARACTER

INTEGER•4

Character
(returns a
character that has
the ASCII value
specified by the
argument; see
Chapter 2
for additional
information on
character
functions)

CHAR

LOGICAL•l
INTEGER•2
INTEGER•4

CHARACTER

Nworkers
(returns the
total number of
processes
executing a
routine)

NWORKERS

Sizeof

SIZEOF

Functions

(returns the
number of bytes
of storage used
by the argument)

INTEGER•4

Anything with
a valid data
type, except
assumed-size
arrays or
passed-length
characters

INTEGER•4

VAX FORTRAN Language Summary

D-43

Table D-3 (Cont.):

VAX FORTRAN Intrinsic Functions
No. of
Generic
Arguments Name

Specific
Name

Type of
Argument

Type of
Result

ASCII Value
(returns the ASCII
value of the
argument; the
argument must be
a character
expression that
has a length of 1;
see Chapter 2
for
additional
information on
character
functions)

ICHAR

CHARACTER

INTEGER*4

Character relationals
(ASCII collating
sequence)

2
2

LLT
LLE
LGT
LGE

CHARACTER
CHARACTER
CHARACTER
CHARACTER

LOGICAL*4
LOGICAL*4
LOGICAL*4
LOGICAL*4

Functions

D.4

2
2

System Subroutine Summary
The VAX FORTRAN system provides subroutines that you call in the same
manner as a user-written subroutine. These subroutines are described in
this section .
The subroutines supplied are as follows:

D-44

VAX FORTRAN Language Summary

DATE

Retu rn s a 9-byte string conta ining the ASCII representation of th e
current da te in the fo rm dd-mmm -yy.

ID ATE

Returns three integer va lues represen ting the current m onth , day,
an d year .

ERRS NS

Returns in fo rm ation about the most recentl y detected error conditio n .

EXIT

Terminates the execution of a program and return s control to the
o perating system .

SECN DS

Provides system time of da y, or elapsed time, as a floa ting-poin t
value in seconds.

TIME

Returns an 8-byte string containing th e ASCII re presentation of th e
current time in hours, min utes, and seconds, in th e fo rm h h :mm :ss.

RAN

Returns the nex t n um ber from a sequence of pseudo random
n umbers of u niform distrib ution over the range 0 to 1.

MVBITS

Tra n sfers a bit fie ld fr om on e storage loca tion to anoth er.

References to integer arguments in the following subroutine descriptions
refer to arguments of either INTEGER*4 data type or INTEGER*2 da ta
type. However, the arguments must be either all INTEGER*4 or all
INTEGER* 2. In general, IN TEGER* 4 variables or array elements m ay be
used as in pu t values to these subroutines if their values are within the
INTEGER*2 ra nge.

D.4.1

DATE Subroutine
The DATE subroutine obtains the current date as set within the system.
The call to DATE takes the following form:
CALL DATE (buf )

but
Is a 9-byte variable, array, array elemen t, or character substring. The date
is returned as a 9-byte ASCII character string taking the following fo rm :
dd -mmm- yy

dd
Is the 2-digit date.

VAX FORTRAN Language Summary

D-45

mmm
Is the 3-letter mon th specification .

yy
Is the last two digits of the year.

D.4.2

IDATE Subroutine
The IDATE subroutine returns three integer values representing the
current month, day, and year. The call to IDATE takes the following form:
CAL L I DATE( i, j ,k)

If the current da te were October 9, 1988, the values of the integer variables
upon return would be as follows:
= 10
j = 9

k = 88

D.4.3

ERRSNS Subroutine
The ERRSNS subroutine returns information about the most recent error
that has occurred during program execution. The call to ERRSNS takes
the following form:
CALL ERRS NS (fnum , rmssts,rmsstv , i unit , condval)

fnum
Is an integer variable or array element in which the most recent FORTRAN
error number is stored. VAX FORTRAN error numbers are listed in the
VAX FORTRAN User Manual.

A zero is returned if no error h as occurred since the last call to ERRSNS,
or if no error has occurred since the start of execution .
rmssts
Is an integer variable or array element in which the RMS completion
status code (STS) is stored, if the last error was an RMS I/O error.
rmsstv
Is an integer variable or array element in which the RMS status value
(STV) is stored, if the last error was an RMS I/O error. This status value
provides additional status information.
D-46

VAX FORTRAN Language Summary

iunit
Is an integer variable or array element in which the logical unit number is
stored, if the last error was an I/O error.

condval
Is an integer variable or array element in which the actual VAX condition
value is stored.
Any of the arguments can be null. If the arguments have an INTEGER*2
type, only the low-order 16 bits of information are returned. The saved
error information is set to zero after each call to ERRSNS.

D.4.4

EXIT Subroutine
The EXIT subroutine causes program termination, closes all files, and
returns control to the operating system. A call to EXIT has the form:
CALL EXIT [(exit-st atus )]

exit-status
Is an optional integer argument you can use to specify the image exitstatus value.

D.4.5

SECNDS Subroutine
The SECNDS function subprogram returns the system time in seconds as a single-precision, floating-point value, minus the value of its
single-precision, floating-point argument. The call to SECNDS takes the
following form:
y = SECNDS(x)

y
Is set equal to the time in seconds since midnight, minus the user-supplied
value of x.

The SECNDS function can perform elapsed-time computations. For
example:

VAX FORTRAN Language Summary

D-4 7

START OF TIMED SEQUENCE
T1 = SECNDS (0 . 0)

CODE TO BE TIMED
DELTA = SECNDS (T1)

DELTA gives th e elapsed time.
The value of SECNDS is accurate to 0.01 second, which is the resolution
of the system clock.
The time is computed from midnight. The SECNDS subroutine also
produces correct results for time intervals that span midnight.
The 24 bits of precision provides accuracy to the resolution of the system
clock for about one day. However, loss of significance can occur if you
attempt to compute very small elapsed times late in the day. More precise
timing information can be obtained using the following Run-Time Library
procedures:
•
•
•

D.4.6

LIB$INIT_TIMER
LIB$SHOW_ TIMER
LIB$STAT_ TIMER

TIME Subroutine
The TIME subroutine returns the current system time as an ASCII string.
The call to TIME takes the following form:
CALL TIME (buf)

buf
Is an 8-byte variable, array, array element, or character substring.

The TIME call returns the time as an 8-byte ASCII character string having
the following form:
hh :mm :ss

hh
Is the 2-digit hour indication .
mm
Is the 2-digit minute indication.

D-48

VAX FORTRAN Language Summary

ls the 2-digit second indication.
For example:
10 45 23

A 24-hour clock is used .

D.4. 7 RAN Subroutine
The RAN function is a general random number generator of the multiplicative congruential type. The result is a floating -point number that is
uniformly distributed in the range between 0.0 inclusive and 1.0 exclusive.
The call to RAN takes the following form:
y = RAN(i)

y
Is set equal to the value associated, by the function, with the argument i.
The argument i is called the seed. It must be an INTEGER*4 variable or
INTEGER*4 array element.
The argument should initially be set to a large, odd integer value. The
RAN function stores a value in the argument that it later uses to calculate
the next random number.
There are no restrictions on the seed, although it should be initialized
with different values on separate runs in order to obtain different random
numbers. The seed is updated automaticall y, and RAN uses the following
algorithm to update the seed passed as the parameter:
SEED= MOD (69069 *SEED+ 1. 2**32)

The value of SEED is a 32-bit number whose high-order 24 bits are
converted to floating point and returned as the result.

0.5 Bit Functions
VAX FO RTRAN provides intrinsic functions for manipulation of the
bits in the binary patterns that represent integer data types. For more
information, refer to Table D-3 .

VAX FORTRAN language Summary D-49

D.5.1

Bit Position
Integer data types are represented internally in binary twos complement
notation. Bit positions in the binary representation are numbered from
right (least significant bit) to left (most significant bit); the rightmost bit
position is numbered 0. A bit in a binary pattern has a value of 0 or 1.

D.5.2

Bit Function Arguments
The intrinsic functions IAND, IOR, IEOR, and NOT operate on all of
the bits of their argument or arguments. Bit 0 of the result is the result
of applying the specified logical operation to bit 0 of the argument or
arguments. Bit 1 of the result is the result of applying the specified logical
operation to bit 1 of the argument or arguments, and so on for all of the
bits of the result.
The shift functions ISHFT and ISHFTC shift binary patterns. A positive
shift count indicates a left shift, while a negative shift count indicates a
right shift. ISHFT specifies a logical shift; bits shifted out of one end are
lost and zeros are shifted in at the other end. ISHFTC performs a circular
shift; bits shifted out at one end are shifted back in at the other end.
The functions IBSET, IBCLR, BTEST, and IBITS and the subroutine
MVBITS operate on bit fields. A bit field is a contiguous group of bits
within a binary pattern. Bit fields are specified by a starting bit position
and a length. A bit field must be entirely contained in its source operand.
For example, the integer 47 is represented by the following:
Binary pattern:

0 ... 0101111

Bit position :

n ... 6543210

Where n is the number
of bit positions in the numeric storage unit .

You can refer to the bit field contained in bits 3 through 6 by specifying a
starting position of 3 and a length of 4.
Negative integers are represented in twos complement notation. For
example, the in teger -47 is represented by the following:

D-50

VAX FORTRAN Language Summary

Binary patte rn :

0 ... 10 1000 1

Bit positi o n :

n ... 65432 10

Wh ere n is th e number
of bit positio ns in th e nume ri c s to rage unit .

Notice that the value of bit position n is as fo ll ows:
10-

for a negative number
for a non -negative number

All the high -order bits in the pattern from the last significant bit of the
value up to bit n are the same as bit n.
IBITS and MVBITS operate on general bit fields. Both the starting position
of a bit fiel d and its length are arguments to these intrinsics. IBSET,
IBCLR, and BTEST operate on 1-bit fields. They do not require a length
argumen t.
For optimum selection of performance and memory requirements,
FORTRAN provides two integer data types: INTEGER*2 requi res two
bytes of storage, while INTEGER*4 requires four bytes. The bit m anipulation functions each have a generic form that operates on either of the two
integer types and a specific form for each type. When you use the intrinsic
func tions that refer to bit positions or that shift binary patterns within a
storage unit, you must be careful that you do not crea te a value that is
outside th e range of integers representable by the data type. For example:
I NTEGER*2 I , J
I = 1
J = 17
I = ISHFT(I ,J)

The variables I and J have INTEGER*2 data type. Therefore, the generic
function ISHFT maps to the specific function IISHFT, which returns an
INTEGER*2 result. INTEGER*2 results must be in the range -3 2768 to
32 767, bu t the value 1, shifted left 17 positions, yields the binary pattern
1 follow ed by 17 zeros, which represents the integer 131072. (This would
be valid if eith er I or J or both were INTEGER*4 because in both cases
ISHFT would m ap to the specific func tion JISHFT, which returns an
INTEGER*4 valu e.)
If ISHFT is called with constant arguments, it returns an INTEGER*4

value.

VAX FORTRAN Language Summary

0-51

D.5.3

MVBITS Subroutine
The MVBITS subroutine transfers a bit field from one storage location
(source) to a field in a second storage location (destination). The call to
MVBITS takes the following form:
CALL MVB ITS (rn ,i , len , n , j )

m
Is an integer variable or array element that represents the source location
(the location from which a bit field is transferred).
I

Is an integer expression that identifies the first bit position in the field
transferred from m .
fen

Is an integer expression that identifies the length of the field transferred
from m.

n
Is an integer variable or array element that represents the destination
location (the location to which a bit field is transferred) .
1
Is an integer expression that identifies the starting position, within n, for
the bits being transferred .

The MVBITS subroutine transfers len bits from positions i through i+len-1
of the source location (m) to positions j through j+len- 1 of the destination
location (n). Other bits of the destination location and all of the bits of the
source location remain unchanged . The values of i+len must be less than
32, and j+len must be less than or equal to 32.

D-52

VAX FORTRAN Language Summary

Index
Access, shared

See Subtraction or unary minus operator
See Exclamation point
See Quotation marks

$
See Dollar sign
*

See Asterisk
**

See Exponentiation operator

+
See Addition or unary plus operator
See Colon

?
See Question mark

I
See Division operator

II
See Concatenation operator

A
ABS intrinsic function • D-36
Absolute Value intrinsic function• D-36
ACCEPT statement• 7-47 to 7-48
ACCESS
INQUIRE statement specifier• 9-25
OPEN statement keyword • 9-4, 9-8

SHARED keyword
on OPEN statement• 9-4, 9-21
Access keys
for indexed fi les
specified in OPEN statement• 9-15
Access modes
direct in OPEN statement keywords• 9-2
ACOSD intrinsic function• D-34
ACOS intrinsic function• D-34
Actual arguments
aggregate field references used as• 2-37
external procedure names used
as• 4-21 to 4-22
unsubscripted array used as• 2-29
Addition operator(+)• 2-42 to 2-44, 2-51
Adjustable arrays• 2-29
in RECORD statements• 2-38
A field descriptor• 8-29 to 8-31
Aggregate assignment statement• 3-6
Aggregate field reference
examples• 2-38 to 2-39
format of•2-36 to 2-37
Aggregate reference• 2-39 to 2-41
AIMAG intrinsic function• D-39
AINT intrinsic function• D-36
Allocation
see File storage allocation
Alternate return argument• 6-9
AMAXO intrinsic function • D-40
AMINO intrinsic function• D-40
.AND .
See logical operators
ANINT intrinsic function• D-37

lndex-1

ANSI Standard
comparison with ISO Standard• 1-1
VAX FORTRAN extensions of• 1-1
APPEND
OPEN statement keyword value• 9-4
'APPEND'
OPEN statement keyword value • 9-8
Arc Cosine (degree) intrinsic function • D-34
Arc Cosine intrinsic function • D-34
Arc Sine (degree) intrinsic function• D-34
Arc Sine intrinsic function• D-34
Arc Tangent (degree) intrinsic function• D-35
Arc Tangent intrinsic function• D-35
Arguments
See also Actual arguments, Dummy arguments
aggregate field references as• 2-37
associating array elements with• 2-25
associating variables with• 2-22
bit function arguments• D-50 to D-52
external procedure names used
as• 4-21 to 4-22
general description• 6-2 to 6-11
alternate return arguments• 6-9
arrays• 6-3 to 6-5
assumed-size arrays• 6-6
character arrays• 6- 7
defaults for arguments
passing• 6-9 to 6-11
Hollerith and character constants• 6-8
overview• 6-2
passed-length character arguments• 6-7
intrinsic function names used as• 4-23
use of built-in functions
argument list functions (%VAL, %REF,
%DESCR) • 6-9 to 6-11
%LOC function• 6-11
Arithmetic assignment statement• 3-1 to 3-3
Arithmetic expressions• 2-42 to 2-46
compile-time• 4-27, 4-28
data type ranking• 2-45
in relational expressions• 2-48
operator precedence• 2-43 to 2-44
order of evaluation• 2-43 to 2-45
rules governing typing of• 2-45 to 2-46
Arithmetic IF statement• 5-16
Arithmetic operators
in expressions• 2-42 to 2-44, D-1

2-lndex

Array element
defining values of• 3-1
Array name
references to• 2-39 to 2-41
unsubscripted in a DAT A statement• 4-6
Array references
in dimension bounds expressions• 2-26
without subscripts• 2-29
with subscripts• 2-27
Arrays
addressing character substrings in elements
of• 2-30 to 2-31
adjustable• 2-29
arrangement of elements• 2-27
associating two or more• 2-25
assumed-size• 2-30
data types of• 2-1
data typing• 2-29
declarators• 2-25 to 2-26
defining in a COMMON statement• 4-4
defining with character type declarations• 4-11
definition of• 2-4
dimension bounds expressions• 2-25 to 2-26
dimensioning • 4-12
elements as scalar references• 2-39
establishing with subprogram references• 2-25
general description• 2-24 to 2-25
inability to dimension within CONTEXT_
SHARED• 10-3
initializing with DAT A statements• 4-5 to 4-8
in structure declaration blocks• 2-32
making equivalent• 4-14 to 4-16
references to in statements• 2-29
subscripts• 2-27
unsubscripted array names
usage restrictions• 2-29
ASCII character set• B-2
ASCII collating sequence functions• 0-45
ASCII constants
assigned in DAT A statements• 4- 7
ASCII Value intrinsic function• 0-45
ASIND intrinsic function • D-34
ASIN intrinsic function • 0-34
Assigned GO TO statement• 5-14 to 5-1 5
establishing symbolic statement labels
for• 3-7 to 3-8

Assignment statements
aggregate• 3 - 6
arithmetic• 3 - 1 to 3-3
character• 3 - 4 to 3- 5
logical • 3-4
ASSIGN statement • 3-7 to 3-8
ASSOC IA TEV ARI ABLE
OPEN statement keyword• 9-4, 9-8
Association
of arrays• 2- 24
of variables• 2-22
Assumed-size arrays• 2-30
Asterisk ( *)
comment line indicator• 1-8, 1-13
format specifier
in list-directed 1/0 • 7-2, 7-5
multiplication operator• 2-42 to 2-44 , 2-51
upper bound of array• 2- 25
Asterisk ( *) length specifier
for dummy argument or function name• 4 - 11
in numeric type declarations• 4-9
AT AN2 intrinsic function• D-35
AT AND2D intrinsic function• D-35
AT AND intrinsic function• D-35
AT AN intrinsic function• D-35

B
BACKSPACE statement
See also REWIND statement
general description• 9-35
Binary operators
definition of• 2-43
Bit Clear intrinsic function• D- 42
Bit Extraction intrinsic function• D-42
Bit field transfers
MVBITS subroutine• D-53
Bit functions
general information about• D-50 to D-52
Bit Set intrinsic function• D-42
Bit Test intrinsic function• D-42
Bitwise AND intrinsic function• D-4 1
Bitwise Circular Shift intrinsic function• D-43
Bitwise Complement intrinsic function• D-4 1
Bitwise Exclusive OR intrinsic function• D-4 1
Bitwise OR intrinsic function• D-41
Bitwise Shift intrinsic function• D-42

BLANK
INQUIRE statement specifier• 9 - 26
OPEN statement keyword• 9-4, 9- 8
Blank common block• 4 - 3
Blank control editing
BN and BZ edit descriptors• 8-10 to 8-11
Blank lines• 1-8, 1-13
Block DAT A statement• 4-2 to 4-3
BLOCK DAT A statement
position after OPTIONS statement• 1-19
Block DAT A subprogram• 4 - 2 to 4 - 3
BLOCK DAT A subprogram
forcing linker to search libraries• 4-21
Block IF constructs• 5-17 to 5-24
Blocks
OPEN keywords affecting• 9-2
BLOCKSIZE
OPEN statement keyword • 9-4, 9 - 9
BN edit descriptor• 8-10
BTEST intrinsic function • D-42
BUFFERCOUNT
OPEN statement keyword• 9-4, 9-9
Built-in functions
argument list functions
% VAL, %REF, %DESCR • 6-9 to 6-11
%LOC function• 6-11
BYTE
as a data type• 2-2
as storage location• 2-3
declaring data type• 4-8 to 4-10
equivalence with LOGICAL* 1 • 4-9
BZ edit descriptor• 8-11

c
c
to begin a compiler directive• 1- 13
See also Compiler directives
to indicate a comment line• 1-8, 1- 13
Calendar dates
subroutines for calculating
DATE and IDATE • D-46
CALL statement• 5-2 to 5-3
use of return args • 5-25, 5-27
use with ENTRY statement• 6-24
use with SUBROUTINE statement• 6-18 ,
6-20

lndex-3

CALL statement (cont'd.)

Characters (cont'd .)

using names declared in INTRINSIC
statement• 4-23
using names specified in EXTERNAL
statement• 4-21
CARRIAGECONTROL
INQUIRE statement keyword• 9-26
OPEN statement keyword• 9-4, 9-10
Carriage control characters• 8-38 to 8-39
Carriage control editing• 8-38 to 8-39
CDD$TOP•1-16
COD records• 1-15
CDEC$ IDENT directive• 10-10
CDEC$ PSECT directive• 10-11 to 10-12
CDEC$ SUBTITLE directive• 10-13
CDEC$ TITLE directive• 10-13
CHARACTER
data type
definition• 2-1
representation in memory • C-11
storage requirement• 2-2 to 2-3
Character arguments
passed length• 2-23
Character assignment statement• 3-4 to 3-5
Character comparison library functions
LEN , INDEX, ICHAR, CHAR• 6-30 to 6-32
See also Lexical comparison functions
Character constants
as actual arguments• 6-8
assigned in DAT A statements• 4-7
general description• 2-18 to 2- 19
upper and lowercase letters in• 1-9
use of space within • 1-9
Character editing (A ,H) • 8-29 to 8-32
character constants• 8-32
Character expressions• 2-4 7
compile-time• 4-27
in relational expressions• 2-48
CHARACTER FUNCTION statement• 6-15
Character intrinsic function• 0-44
Character operators• 2-4 7
in expressions• 0 - 1
Character relational intrinsic functions• 0-45
Characters
See also uppercase characters , lowercase
characters
declaring variables• 4-10

defining values of• 3-1
in character and Hollerith constants • 1-9
printable/nonprintable • 1-9
Character set • 1-8
ASCII• B-2
FORTRAN • B-1
Radix-50 • B-4 to B-5
Character storage units• 2-2
Character substrings
addressing in variables, arrays, and array
elements• 2-30 to 2-31
as scalar references• 2-39
definition• 2-4
making equivalent• 4-17 to 4-20
Character type declaration statement
general description• 4-10 to 4- 12
CHAR function• 6-32
CHAR intrinsic function• 0-44
CLOSE statement
general description• 9-23 to 9-24
CMPLX intrinsic function• 0-39
Coding form • 1- 10
Colon( :)
edit descriptor• 8-38
Columns
comment indicator position • 1-13
continuation indicator position • 1-14
in a line• 1-2
of a statement label field• 1-13
sequence number field position• 1-15
statement field position • 1-14
Comment • 1-7 to 1-8
allowable characters in• 1-9
in a parallel DO-loop • 10-4
Comment line indicator
Din column 1•1-14
general description• 1-7
common block
names in COMMON statement• 4-4
Common block
COMMON and EQUIVALENCE
interaction• 4-20
default attributes of• 10-12t
establishing order of contents• 4-4
initializing values in• 4-2 to 4-3

4-lndex

Common block
in parallel processing
specifying private default shareability •
10-7
specifying private shareability • 10- 6
specifying shared default shareability •
10-8
specifying shared shareability • 10-7
modifying attributes of• 10-11
modifying shareability in parallel
DO-loop• 10-2 to 10-7
Common Data Dictionary
See DICTIONARY statement
Common logarithm intrinsic function • D-33
COMMON statement
See also Common block
establishing arrays with• 2 - 24, 2-25
establishing variables with• 2-22
general description• 4-3 to 4-5
interaction with EQUIVALENCE• 4-20
using unsubscripted array names• 2-29
Compilation options
overriding FORTRAN command
options • 1-18 to 1- 19
Compiler directives• 10-1 to 10-13
Compile-time constant
expressions• 4-27 to 4-28
COMPLEX
declaring data type• 4-8 to 4-1 0
COMPLEX•16
constants• 2-14
data type
representation in memory• C-8 to C-10
storage requirement• 2-2 to 2-3
D_floating and G_floating
implementations• 2-4
COMPLEX•8
constants• 2-13 to 2-14
data type
definition• 2-1
representation in memory• C-8
storage requirement• 2-2 to 2-3
Complex Conjugate intrinsic function• D- 39
Complex data editing• 8-25
Complex entities
in relational expressions• 2-48
Complex from Two Arguments function

Complex from Two Argum ents function (cont'd.)
See CMPLX intrinsic function , DCMPLX intrinsic
function
Complex numbers
intrinsic functions that operate on• D-39
intrinsic functions to operate on• 6-26
Computed GO TO statement• 5- 13 to 5-1 4
Concatenation operator ( / /) • 2-4 7 , 2-51
CONJG intrinsic function• D-39
Connect ions, logical
to logical 1/0 units
explicitly by means of OPEN• 9-22
Constants
as scalar references• 2-39
assigning symbolic names with PARAMETER
statement• 4-26 to 4-28
character• 2-18
complex• 2-13 to 2-15
data types of • 2-1
definition• 2-4
hexadecimal• 2-15 to 2-18
Hollerith• 2-19 to 2-21
initialized by a PARAMETER statement• 2-46
integer• 2-5
logical• 2-18
octal•2-15to 2-18
Radix-50 • B-4
real• 2- 8 to 2-13
specifying data types of• 2-5 to 2-21
using a symbo lic name• 4-27
CONTEXT_SHARED directive• 10-3
CONTEXT_ SHARED_ ALL directive• 10-3
Continuation indicator field • 1-10, 1-14
Continuation line• 1-2
effect on statement labels• 1-13
in debug source statements • 1-14
indicator in source code• 1-14
in included files• 1-17
use of in compiler directive• 10-1
CONTINUE statement• 5-3
Control characters• 1-9
Control list parameters
general description• 7-2 to 7-3
Control statements• 5-1 to 5-28
See also CALL, RETURN
in parallel DO-loop• 10-4
Control transfer
FORTRAN control statements• 5-1 to 5-28

lndex-5

Control transfer (cont'd.)
with DO-loops • 5-8
Conversion
of data types in arithmetic assignments• 3-3t
with FORMAT statements• 8-1
Conversion to COMPLEX• 16 function• D-39
Conversion to COMPLEX •8 function• D-39
Conversion to REAL* 16 function• D-38
Conversion to REAL•4 function• D-37
Conversion to REAL•8 function• D- 38
COSD intrinsic function • D-34
COSH intrinsic function• D-35
Cosine (degree) intrinsic function • D-34
Cosine intrinsic function• D-34
COS intrinsic function• D-34
CPAR$ CONTEXT_SHARED directive• 10-3
CPAR$ CONTEXT_SHARED_ ALL directive• 10-3
CPAR$ DO_PARALLEL directive• 10-4 to 10-5
CPAR$ LOCK OFF directive• 10-5 to 10-6
CPAR$ LOCK ON directive• 10-5 to 10-6
used to resolve data dependences• 10-5
CPAR$ PRIVATE directive• 10-6 to 10-7
CPAR$ PRIVATE _ALL directive• 10-7
CPAR$ SHARED directive• 10-7
CPAR$ SHARED_ ALL directive• 10-8
Critical region
in a parallel DO-loop• 10-5

D
D
in REAL•8 constants• 2-11
D_floating data implementation
representation in memory
COMPLEX• 16 • C-8 to C-9
REAL•8•C-3 , C-5
with COMPLEX•16 data type• 2-4, 2-14
with REAL•8 data type•2-4, 2-10
/D_LINES qualifier• 1-14
Data
as stored in memory
by VAX FORTRAN•C-1 to C-12
editing
with FORMAT statements• 8-1
retaining after END or RETURN• 4-30 to 4-31
Data dependences
in a parallel DO-loop• 10-5

6-lndex

Data items
as scalar references• 2-39
defining values for• 3- 1
definition• 2-4
identified by symbolic names• 1-7
DATA statement
general description• 4- 5 to 4-8
to define arrays and elements• 2-25
using unsubscripted array names• 2-29
Data type declaration statement
See also Type declaration statement
character type declarations• 4-10 to 4-12
numeric type declarations• 4-8 to 4-10
use to establish arrays• 2-24
using unsubscripted array names• 2-29
Data types
ability of entities to have• 1-7
conversion in arithmetic assignment
statements • 3-3t
declaration within structures• 4-34
default data types of undeclared names• 4-22
definition of different types• 2-1 to 2-2
establishing in arithmetic
expressions• 2-45 to 2-46
length specifiers• 2-2
rank in arithmetic expressions• 2-45
specifying for arrays• 2-28
specifying for constants• 2-5 to 2-21
specifying for variables• 2-22, 2-23 to 2-24
Dates , calendar
subroutines for calculating
DA TE and IDA TE• D-46
DA TE subroutine• D-46
DBLE intrinsic function• D-38
DCMPLX intrinsic function• D-39
D debugging statement indicator
in column 1 • 1-14
Debugging statements• 1-14
Declarators, array• 2- 25 to 2-26
DECODE statement• A-1 to A-3
DEF AUL TFILE
INQUIRE statement keyword• 9-25
OPEN statement keyword• 9-4, 9-10
Defaults
argument passing defaults• 6-10
data type of undeclared names• 4-22
field descriptors vs. 1/0 list elements• 8-33

DEFINE FILE statement• A-3 to A-4
DELETE
file description• 9-23
DELETE statement
general description• 9-36 to 9-37
Delimiting periods
of logical values• 2- 50
of relational values• 2-48
%DESCR built-in function• 6-10
D field descriptor• 8-21
in complex data editing• 8-25
DFLOA T intrinsic function• D-38
DICTIONARY statement• 1-15 to 1-16
DIMAG intrinsic function• D-39
Dimension bounds expressions
See Arrays
Dimensions
array limits• 2-24
declaring of an array• 2-25 to 2-26
DIMENSION statement
general description• 4-12 to 4- 13
use to establish arrays• 2-24
DIM intrinsic function• D-40
DIRECT
INQUIRE statement specifier• 9-27
OPEN statement keyword value• 9-4
Direct access FIND statements• A - 5
Direct access mode
OPEN statement keywords• 9-2
Direct access READ statements• 7- 26 to 7-27
Direct access WRITE statements• 7-39 to 7-40
Directives
See Compiler directives
'DIRECT'
OPEN statement keyword value• 9- 8
DISP
CLOSE statement keyword• 9-23
DISPOSE
CLOSE statement keyword• 9-23
OPEN statement keyword• 9-4, 9-11
Division operator ( /) • 2-42 to 2-44, 2-51
Dollar sign ($)
delimiter for namelist record• 7-20
edit descriptor• 8-37 to 8- 38
in a symbolic name• 1- 6
DO-loop
See also Parallel DO-loop

DO-loop (cont'd .)
transferring control• 5-8
DO statements • 5-3 to 5-1 2
indexed• 5-4 to 5-9
pretested indefinite
DO WHILE• 5-9 to 5-11
DOUBLE COMPLEX
declaring data type• 4-8 to 4-10
DOUBLE PRECISION
declaring data type• 4-8 to 4- 10
DO WHILE statement• 5-9 to 5-11
DO_ PARALLEL directive• 10-4 to 10-5
DPROD intrinsic function• D-39
DREAL intrinsic function • D-39
Dummy arguments
aggregate field references used as• 2-37
inability to declare in
CONTEXT_ SHARED• 10-3
unsubscribed array names used as• 2-29
using asterisk (•) length specifier• 4-11

E
Edit descriptors
summary• 8- 6 to 8- 7
E field descriptor• 8-19
in complex data editing• 8-25
ELSE IF THEN statement
block IF constructs• 5-17 to 5-24
ELSE statement
block IF constructs• 5-17 to 5-24
ENCODE statement• A-1 to A-3
END DO statement• 5-11 to 5-12
ENDFILE statement• 9-35 to 9- 36
END IF statement
block IF constructs• 5-17 to 5-24
END MAP statement• 4-39
End-of-file condition
reporting with IOST AT value• 7- 9
transferring control with END specifier• 7-10
End-of-file record
ENDFILE statement• 9-35 to 9-36
END specifier
in 1/0 statements• 7-10
END statement
general description• 5-12
with BLOCK DAT A statement• 4-3

lndex-7

END statement (cont'd .)
with FUNCTION statement• 6-15
with SUBROUTINE statement• 6-18
END UNION statement• 4- 39
ENTRY statement• 6-21 to 6-24
use with FUNCTION statement• 6-17
use with SUBROUTINE statement• 6- 19
using unsubscripted array names• 2-29
.EQ.
See relational operators
EQUIVALENCE statement
associating arrays with• 2-25
associating variables with• 2-22
contrasted with union declaration• 4-40
general description• 4-13 to 4-20
interaction with COMMON• 4 - 20
use of unsubscripted arrays with• 2- 22, 2- 25
using unsubscripted array names• 2-29
.EQV .
See logical operators
ERR
BACKSPACE statement keyword• 9-35
CLOSE statement keyword• 9 - 23
DELETE statement keyword • 9- 36
ENDFILE statement keyword• 9-35
1/0 statement specifier• 7-10
INQUIRE statement specifier• 9-27
OPEN statement keyword• 9-4, 9- 12
REWIND statement keyword• 9- 34
UNLOCK statement keyword• 9-38
Error condition
during l/0•7-9 , 7-10
Error handling
subroutine for obtaining error information
ERRSNS subroutine• D-4 7
user controls in 1/0 statements
ERR, END, and IOSTAT specifiers• 7-9 ,
7-10
ERRSNS subroutine • D-4 7
Exclamation point (!)
comment indicator• 1-8, 1-13
Executable statements• 1-2 , 1-4
Execution , program
temporarily suspending
(PAUSE)• 5-24 to 5-25
term inating
EXIT• 0-48
STOP•5-27

8-lndex

EXIST
INQUIRE statement specifier• 9-27
EXIT system subroutine• D-48
EXP intrinsic function• D-33
Explicit formatting
1/0 statement specifier• 7-4 to 7-5
Exponential intrinsic function• D-33
Exponentiation operator ( ••) • 2-42 to 2-44,
2-51
Exponents
in REAL•4 constants• 2-8
in REAL•8 constants• 2- 10
in REAL• 16 constants• 2-12
Expressions, FORTRAN
See also Arithmetic expressions, Character
expressions, Logical expressions ,
Relational expressions
as scalar references• 2-39
compile-time constant
expressions• 4-27 to 4- 28
data types of• 2-1
definition of• 2-42
expression operators
summary of• D-1 to D-2
variable FORMAT• 8-9 to 8-10
Extended ranges , DO-loop• 5-9
EXTENDSIZE
OPEN statement keyword• 9-4 , 9-12
External field separators• 8-40 to 8-4 1
External procedure names
as arguments• 4-21 to 4-22
duplicating intrinsic function names• 4-2 1
External procedures
invoking with CALL• 5-2
unsubscripted array names as dummy
arguments• 2-29
EXTERNAL statement• 4-21 to 4-22
/NOF77 implementation• A-8 to A-9
to search object libraries for block data
subprograms• 4 - 3

F
F_floating data implementation
representation in memory
COMPLEX •8 • C-8
REAL•4 • C- 4

F field descriptor• 8-17
in complex data editing• 8-25
Field
in FORTRAN source code• 1-9 to 1- 15
Field declarations
allowable entities• 4-35
Field descriptors
defaults for 1/0 list elements• 8-33
summary• 8- 6 to 8-7
Field namelist • 4-34
Field names • 4-34
in structure declarations• 4-38
Field references
See Record and field references
Fields
definition in structure
declarations• 4-33 to 4-38
initialization of unnamed fields• 2-33
Fields, unnamed
use of %FILL• 2-33
Field separators, external• 8-40 to 8-41
File
combining at compilation• 1- 17 to 1-18
deleting records from
DELETE statement• 9-36 to 9-37
disposition
CLOSE statement keywords• 9-23
INCLUDE files• 1-17 to 1-18
processing options
OPEN statement keywords• 9-2
properties, inquiring about
INQUIRE statement• 9-24 to 9- 33
providing a listing header for• 10-13
record description options, 1/0
OPEN statement keywords• 9-2
repositioning
BACKSPACE statement• 9-35
repositioning with REWIND statement• 9-34
status options
OPEN statement keywords• 9-2
FILE
INQUIRE statement keyword• 9-25
OPEN statement keyword• 9-4, 9-13
File-handling commands
BACKSPACE statement• 9-35
CLOSE statement• 9-23 to 9-24
INQUIRE statement• 9-24 to 9-33
OPEN statement• 9-2 to 9-23

File-handling commands (cont'd .)
REWIND statement• 9-34
File sharing
SHARED keyword (OPEN statement)• 9-4,
9-21
File specifications
OPEN statement keywords• 9-2
File status
CLOSE statement keywords• 9-23
OPEN statement keywords
DISPOSE• 9-4, 9-11
STATUS or TYPE• 9-4, 9-22
File storage allocation
OPEN statement keywords• 9-2
%FILL• 2-33, 4-34, 4-38
FIND statement• A-5
Fixed-format • 1-10 to 1-11
Fixed-length records
RECORDTYPE keyword
(OPEN statement)• 9-4, 9-20 to 9-21
Fix intrinsic function• D-38
Floating-point data types
emulation of• 2-4
representation in memory• C-3 to C-1 O
FLOAT intrinsic function• D-38
FMT format specifier
in 1/0 statements• 7-4
FORM
INQUIRE statement specifier• 9-28
OPEN statement keyword• 9-4, 9- 13
Format
coding with fixed format • 1-10 to 1-11
coding with tab format • 1-11 to 1-13
Formats
passed length• 2-2
run-time• 8-41 to 8-42
Format specification separators• 8-39 to 8-40
Format specifier
control list parameter
in 1/0 statements• 7-4
FORMAT statements
arithmetic expressions in • 8-9 to 8-1 O
description of use• 8-1
external field separators• 8-40 to 8-41
field and edit descriptors
additional editing operations
(Q,$ ,:) • 8-36 to 8- 38
blank control editing, (BN,BZ) • 8-1 O

lndex-9

FORMAT statements
field and edit descriptors (cont'd .)
character editing (A,H) • 8-29 to 8-32
counts, repeat• 8-8
integer editing (1,0,Z) • 8-12 to 8-17
logical editing (L) • 8-28
positional editing (X, T, TL, TR)•
8-34to 8-36
real editing (F,E,D,G) • 8-17 to 8-25
scale factor editing (P) • 8-25 to 8-2 7
sign control editing (SP ,SS,S) • 8-11
summary of• 8-6 to 8-7
use of character constants• 8-32
format expressions, variable• 8-9 to 8-10
format specification
separators• 8-39 to 8-40
general rules• 8-2 to 8-3
1/0 lists, interaction with• 8-42 to 8-46
input rules• 8-3
output rules• 8-3 to 8-4
run-time formats• 8-4 1 to 8-42
syntax • 8-4 to 8-6
FORMATTED
INQUIRE statement specifier• 9-28
Formatted 1/0 statements
ACCEPT statement• 7-47
establishing symbolic statement labels
for• 3-7 to 3-8
PRINT statement• 7-48 to 7-49
READ statements
direct access• 7-26
indexed• 7-28, 7-29
internal• 7-31
sequential• 7-15, 7-16
REWRITE statement • 7-45, 7-46
TYPE statement • 7-48 to 7-49
WRITE statements
direct access• 7-39, 7-40
indexed• 7-41, 7-42
internal• 7-43, 7-44
sequential• 7-33, 7-34 to 7-35
FORTRAN-66
VAX FORTRAN support of• 1-1
FORTRAN-77
VAX FORTRAN extensions of• 1-1
FORTRAN character set• 8-1
FORTRAN command (DCL)
/D_LINES • 1-14

10-lndex

FORTRAN command (DCL) (cont'd .)
overriding • 1-15, 1-18 to 1-19
FORTRAN data representation in
memory • C-1 to C- 12
FORTRAN statements• 1-2 to 1-5
assignment statements• 3-1 to 3-8
control statements• 5-1 to 5-28
1/0 statements• 7-1 to 7-49
1/0 statements, auxiliary• 9-1 to 9-38
language summary (alphabetic) • D-2 to 0-32
scalar field references in• 2-37
specification statements • 4-1 to 4-42
supplemental statements
supported to maintain non-VAX FORTRAN
compatibility• A-1 to A-9
Function name
using asterisk (•) length specifier• 4-11
Function references
data types of• 2-1
general description • 6-1 6 to 6-18
types of references to intrinsic functions
specific and generic• 6-25 to 6-30
Functions
See Built-in functions
See Intrinsic functions, system supplied
See Lexical comparison library functions
See Statement functions
FUNCTION statement• 6-15 to 6-18
logical and numeric functions• 6-15
position after OPTIONS statement • 1-19
using unsubscripted array names• 2-29
Function subprograms• 6-15 to 6-18

G
G_floating data implementation
representation in memory
COMPLEX•16 • C-10
REAL•8 • C-6
with COMPLEX•16 data type• 2-4, 2-14
with REAL•8 data type• 2-4, 2-10
.GE .
See relational operators
General directives• 10-10 to 10-13
ordering with statements • 1-3f
Generic references

Generi c references (cont'd .)
to intrinsic function names• 6-26 to 6- 27 ,
6- 28
G field descriptor• 8-22
in complex data editing• 8-25
GO TO statement
establishing symbolic statement labels for
assigned• 3-7 to 3- 8
GO TO statements• 5-12 to 5-15
Group repeat counts
in FORMAT statements• 8-8
.GT .
See relational operators

H
H_ floating data implementation
representation in memory
REAL• 16 • C-7
Hexadecimal constants• 2 - 5 , 2-15 to 2-18
assigned in DAT A statement• 4- 7
data type assignments• 2- 16 to 2-17
H field descriptor• 8-32
Hollerith constants• 2-5, 2-19 to 2- 21
assigned in DAT A statements• 4-7
upper and lowercase letters in • 1-9
use of space within• 1-9
Hollerith Constants
representation in memory• C-11
Hyperbolic Cosine intrinsic function• D- 35
Hyperbolic Sine intrinsic function• D-35
Hyperbolic Tangent intrinsic function• D-35

I
field descriptor• 8-12 t o 8-14
1/0, iterative
See iterative 1/0
1/0 statement components
control list parameters• 7-1 to 7-3
format specifier • 7- 4
1/0 status specifier• 7-9
internal file specifier• 7-4
key-field value specifier• 7-6
key-of-reference specifier• 7-9
logical unit specifier• 7-3

1/0 statement components
control list parameters (cont'd .)
namelist specifier• 7-5
record specifier • 7-6
rules for specifying • 7-3
transfer-of-control specifier• 7-10
1/0 list parameter• 7-11 to 7-14
implied-DO lists• 7-13 to 7-14
interaction with format
controls• 8-42 to 8-46
simple list elements• 7-12
1/0 statements
See also 1/0 statement components, ACCEPT,
FORMAT , OPEN , PRINT, READ , REWRITE ,
TYPE, WRITE
in parallel DO-loop• 10-4
list of• 7- 1
OPEN statement interdependencies
logical unit specifier• 7-4
specifiers
See 1/0 statement components
using unsubscripted array names• 2-29
1/0 status specifier
control list parameter
in 1/0 statements• 7-9
IABS intrinsic value• D-36
IAND intrinsic function• D-41
IBCLR intrinsic function • D-42
IBITS intrinsic function• D-42
IBTSET intrinsic function• D-42
ICHAR function • 6-31
ICHAR intrinsic function • D-45
IDA TE subroutine• D-4 7
IDENT directive• 10-10
IDIMintrinsic function• D-40
IDINT intrinsic function• D-36
IDNINT intrinsic function• D-37
IEOR intrinsic function• D-41
IFIX intrinsic function• D-38
IF statements• 5-15 to 5-24
general descriptions
arithmetic IF• 5-16
block IF• 5-1 7 to 5-24
logical IF • 5-1 7
IF THEN statement
block IF constructs• 5-17 to 5-24
Imaginary Part of Complex function• D-39

lndex-11

IMPLICIT NONE statement• 4-23
IMPLICIT statement
effect of /WARNINGS option• 4-23
general description• 4-22 to 4-23
using to type variables• 2-23
Implied-DO list
See Iterative 1/0
Implied-DO variables
initializing with statements• 4-5 to 4-8
INCLUDE statement• 1-17 to 1-18
Indefinite DO statement, pretested
DO WHILE• 5-9 to 5-11
Indexed DO statement • 5-4 to 5-9
Indexed files
freeing locked records• 9-38
Indexed 1/0 statements
READ statements• 7-28 to 7-30
WRITE statements• 7-4 1 to 7-43
Indexed organization files
access keys
specifier in OPEN statement• 9-15
deleting records from
DELETE statement• 9-36 to 9-37
Indexed WRITE statements• 7-41 to 7-43
INDEX function• 6-3 1
INDEX intrinsic function• D-43
INITIALSIZE
OPEN statement keyword • 9-4, 9-14
INQUIRE statement
general description• 9-24 to 9-33
Integer
constants
in REAL•4 constants• 2-8
octal notation• A- 7
data type
definition• 2-1
representation in memory• C-1, C-2
storage requirements• 2-2 to 2-3
declaring data type• 4-8 to 4-1 O
default data type of undeclared names• 4-22
Integer constants
in COMPLEX•8 constants• 2-13
in REAL•8 constants• 2-10
in REAL• 16 constants• 2-12 , 2-14
used to assign values• 2-6
Integer data type
See also Constants

12-lndex

Integer editing (1,0,Z) • 8-12 to 8-17
Internal file specifier
control list parameter
in 1/0 statements• 7-4
Internal 1/0 statements
ENCODE and DECODE statements•
A-1 to A-3
READ statements• 7-31 to 7-32
WRITE statements • 7-43 to 7-44
Internal WRITE statements• 7-43 to 7-44
INT intrinsic function• D-36
Intrinsic functions, system-supplied
character comparison functions•
6-30to 6-32
complete list of• D-32 to D-45
description of types• 6-2
external procedures of same name• 4-21
lexical comparison functions• 6-32 to 6-33
names used as arguments• 4-23
references, generic• 6-26 to 6-27,
6-28to 6-30
references, specific• 6-25, 6-28 to 6-30
INTRINSIC statement
general description• 4-23 to 4-24
IOR intrinsic function• D- 41
IOSTAT
BACKSPACE statement keyword• 9-35
CLOSE statement keyword• 9-23
DELETE statement keyword• 9-36
ENDFILE statement keyword• 9-35
INQUIRE statement specifier• 9-28
OPEN statement keyword• 9-4, 9-14
REWIND statement keyword• 9-34
specifier in 1/0 statements• 7-9
UNLOCK statement keyword• 9-38
IQINT intrinsic function• D-36
IQNINT intrinsic function• D-37
ISHFTC intrinsic function• D-43
ISHFT intrinsic function • D-42
ISIGN intrinsic function• D-41
ISO Standard
comparison with ANSI Standard• 1-1
Iterative 1/0
implied-DO list• 7-13 to 7-14
iterative count controls
indexed DO statement • 5-4 to 5-9
Iterative processing controls
See DO statements

K
KEEP
file disposition• 9-23
KEY
key-field value specifier
in 1/0 statements• 7-6
OPEN statement keyword• 9-4, 9-15
KEYED
INQUIRE statement specifier• 9-29
OPEN statement keyword value • 9-4
'KEYED'
OPEN statement keyword value • 9-8
Key-field value specifier
control list parameter
in 1/0 statements• 7-6
KEYID specifier
see key-of-reference specifier• 7-9
Key-of-reference specifier
control list parameter
in 1/0 statements• 7-9
Keys, access
specified in OPEN statement • 9-15
KEYx specifier (KEY, KEYEQ, KEYGE, KEYGT,
KEYNXTNE, KEYNXT)
See key-field value specifier

L
Labels
See statement labels
.LE.
See relational operators
L edit descriptor• 8-28
LEN function• 6-30
Length
effect of /EXTEND_SOURCE on sequence
number field • 1-1 5
specifier in data type declarations• 2-2
Length intrinsic function• D-43
LEN intrinsic function• D-43
Lexical comparison library functions
LL T , LLE, LGT, LGE • 6-32 to 6-33
< LF > control character • 1-9
LGE function• 6-32 to 6-33
LGT function• 6-32 to 6-33

Library functions, system-supplied
algorithms used in• D-32
Line
as a physical section of statements• 1- 2
blank• 1-8, 1-13
characters embedded in • 1-9
continuation indicator field• 1-14
entering with fixed format • 1-10 to 1-1 1
entering with tab format• 1-11 to 1-13
format of statement label field • 1-13
sequence number field • 1-15
statement field • 1-14
Linefeed control character• 1- 9
List-directed formatting
1/0 statement specifier• 7-4
List-directed 1/0 statements
ACCEPT statement• 7- 47
READ statements
internal READ• 7- 31
sequential READ • 7- 15, 7-17 to 7-19
WRITE statements
internal WRITE• 7-43 , 7-44
sequential WRITE• 7-33, 7-35 to 7-37
List elements, simple
1/0 list parameter
in 1/0 statements• 7-12
Listing
See Source listing
Listing header
providing for a file• 10-13
/LIST qualifier
to enable TITLE and SUBTITLE compiler
directives • 10-13
Lists, implied-DO
in DAT A statements• 4-5
LLE function• 6-32 to 6-33
LL T function• 6-32 to 6-33
%LOC built-in function• 6-11
Locked records
freeing locked records• 9-38
LOCK OFF directive• 10-5 to 10- 6
LOCK ON directive• 10-5 to 10-6
used to resolve data dependences• 10-5
Lock variable• 10-5
LOG 10 intrinsic function• D-33

lndex-13

Logical
See also Arrays, Constants, Data types, Logical
values, Variables
constants
representation in memory• C-2
storage requirement• 2-2 to 2-3
data type
definition• 2-2
relationship to BYTE data type• 4 - 9
LOGICAL
declaring data type• 4-8 to 4-10
LOGICAL•n
See Logical
Logical assignment statement• 3-4
Logical constants• 2-18
Logical editing (L) • 8-28
Logical elements
See Logical expressions
Logical expressions• 2-49 to 2-52
comp ile-time• 4-27
evaluation of subexpressions• 2-51
order of evaluation• 2-51 to 2-52
Logical functions• 6-15
Logical 1/0 units
CLOSE statement options• 9-23
connection method
explicitly by means of OPEN• 9-22
defining logical unit numbers
DEFINE FILE statement• A-3 to A-4
inquiring about properties
INQUIRE statement• 9-24 to 9-33
OPEN statement options• 9-2
Logical IF statement• 5-1 7
Logical operations
data types that result from• 2-50
Logical operators• 2-50t
in expressions• D-2
Logical scalar memory reference
See Scalar memory reference
Logical unit specifier
control list parameter
in 1/0 statements• 7-3
Logical values
representation in memory• C-2 to C-3
LOG intrinsic function• D-33
Loops , DO
DO statements • 5-3 to 5- 12

14-lndex

Lowercase characters• 1-8
affect on compiler• 1-9
in character and Hollerith constants• 1-9
.LT .
See relational operators

M
Main program
as a program unit• 1-2
Map declaration
general description• 4-38 to 4-41
to establish variables• 2-22
use to establish arrays• 2-25
Mapped field declarations• 2-33
MAP statement• 4 - 38, 4-39
Mathematical functions, intrinsic• D-32 to D-45
MAXO intrinsic function• D-40
MAX 1 intrinsic function• D-40
Maximum intrinsic function• D-40
MAX intrinsic function• D-40
MAXREC
OPEN statement keyword• 9-4, 9-16
Memory diagrams
of structured records• 2-34 to 2-36
Messages
sending to terminal
See PAL1SE statement
MINO intrinsic function• D-40
MIN 1 intrinsic function• D-40
Minimum intrinsic function• D-40
MIN intrinsic function• D-40
Minus operator (-) • 2-42 to 2-44, 2-51
MOD intrinsic function • D-4 1
Multiplication operator ( *) • 2-42 to 2-44, 2-51
MVBITS subroutine• D-53

N
Name
See also symbolic names, entry names
NAME
INQUIRE statement specifier• 9-29
OPEN statement keyword• 9-4, 9-17
Name, structure
using •4-33

NAMED
INQUIRE statement specifier• 9-30
Named c.ommon blocks
establishing order of contents• 4-4
initializing values in• 4-2 to 4-3
Namelist-directed 1/0 statements
See also NAMELIST statement
ACCEPT statement• 7-47
sequential READ statement• 7-15,
7-20 to 7-25
sequential WRITE statement• 7-33 ,
7-37 to 7-38
Namelist specifier
control list parameter
in 1/0 statements• 7-5
NAMELIST statement
general description• 4-24 to 4-25
using unsubscripted array names• 2-29
Names, symbolic
See Symbolic names
Natural Logarithm intrinsic function • D-33
.NE .
See relational operators
Nearest Integer intrinsic function• D-37
.NEQV .
See logical operators
Nested block IF constructs• 5-23 to 5-24
Nested DO loops • 5- 7 to 5- 8
Nested structured declarations
See substructure declarations
Nesting
structure declarations• 4-33 , 4-38
< NEWLINE > control character• 1-9
NEXTREC
INQUIRE statement specifier• 9-30
NINT intrinsic function• D-37
NML specifier
in 1/0 statements• 7-5
/NOF77 qualifier
effect on Do-loops • 5-5
/NOLIST qualifier
in the DICTIONARY statement• 1-16
in the INCLUDE statement• 1-17
Nonexecutable statements• 1-2
Non printable characters• 1-9
/NOOBJECT qualifier
disabling IDENT directive• 10-10

NOSP ANBLOCKS
OPEN statement keyword• 9-4, 9-17
.NOT .
See logical operators
NOT intrinsic function• D-41
NUMBER
INQUIRE statement specifier• 9-30
Number, sequence• 1-15
Numerals • 1-8
Numeric functions• 6-15
Numeric scalar memory reference
See Scalar memory reference
Numeric storage unit• 2-2
Numeric type declarations
general description • 4-8 to 4-10
NWORKERS intrinsic function• D-44

0
0
field descriptor• 8-14
Object libraries
searching for block data subprograms • 4-3
Object module
labeling and identifying with compiler directive•
10-10
Octal constants• 2-5, 2-15 to 2-18
assigned in DAT A statement• 4-7
data type assignments• 2-16 to 2-17
Octal notation ( n )
for integer constants• A- 7
Octal values
1/0 transfers
by 0 field descriptor • 8-14
OPENED
INQUIRE statement specifier • 9-3 1 '
OPEN statement
general description• 9-2 to 9-23
1/0 statement interdependencies
logical unit specifier• 7-4
Operators
See also arithmetic operators , relational
operators
expression operators
summary of• D-1 to D-2
logical• 2-50t

lndex-15

Operators (cont'd .)
precedence in arithmetic expressions•
2-43to 2- 44
precedence in relational expressions• 2-49
used in logical expressions• 2-51
Optimization
effect of VOLATILE statement• 4-41
OPTIONS statement • 1-3, 1-18 to 1-19
.OR.
See logical operators
Order
required of statements• 1-3t
ORGANIZATION
INQUIRE statement specifier• 9-31
OPEN statement keyword• 9-4, 9-17

p
Parallel directives• 10-2 to 10-9
See also NWORKERS function
enabling • 10-2
examples of• 10-8 to 10-9
ordering with statements • 1-3t
Parallel DO-loop • 10-4 to 10-9
/PARALLEL qualifier• 10-2
PARAMETER statement
alternate version of• A-6
defining constants in arithmetic
expressions• 2-46
general description• 4-26 to 4-28
in structure declaration block• 4-32
Parentheses ·
effect in arithmetic expressions•
2-44to 2-45
effect in character expressions• 2-47
in logical expression• 2- 51
Passed-length character arguments• 2-23
Passed-length format, *( *)
for dummy arguments or character
functions• 2-2
Pathnames (COD)• 1-16
PAUSE statement• 5-24 to 5-25
in parallel DO-loop• 10-4
PDP-11 FORTRAN-77
source programs on a VAX FORTRAN
compiler• 1-2
P edit descriptor• 8-25 to 8-27

16-lndex

Periods
delimiting logical values• 2-50
delimiting relational values• 2-48
Plus operator ( +) • 2-42 to 2-44, 2-51
Positional editing (X,T,TL,TR) • 8-34 to 8-36
Positive Difference intrinsic function • D-40
Precedence, operator
effect of parentheses• 2-44 to 2-45
in relational expressions• 2-49
within arithmetic expressions• 2-43 to 2-44
Pretested indefinite DO statement
DO WHILE• 5-9 to 5-11
PRINT
file disposition• 9-23
PRINT statement • 7-48 to 7-49
PRIVATE directive• 10-6 to 10-7
Private entities
using SA VE statement for• 10-7
PRIV A TE_ALL directive• 10-7
Procedure
See subprogram
Program
See program unit
Program execution
temporarily suspending
(PAUSE)• 5-24 to 5-25
terminating
EXIT• D-48
STOP• 5-27
PROGRAM statement
general description• 4-28 to 4-29
position after OPTIONS statement • 1-19
Program unit
assigning a name to main program
unit• 4-28 to 4-29
block data subprogram • 4-2
definition of• 1-2
PSECT directive• 10-11 to 10-12

0
Q

edit descriptor• 8-37
in REAL•16 constants•2-12
QEXT intrinsic function• D-38
QFLOA T intrinsic function• D-38

Question mark (?)
namelist prompt• 7- 22
Quotation marks (")
octal notation for integer constants• A - 7

R
Radix-50
constants and character sets• B-4 to B-5
Random number generator
RAN function • D-50
RAN function• D- 50
READONLY
OPEN statement keyword • 9-4 , 9-18
READ statements
direct access READ• 7-26 to 7-27
formatted• 7-26
unformatted• 7-26, 7-27
indexed READ• 7-28 to 7-30
formatted• 7-28, 7-29
unformatted• 7-28, 7-30
internal READ• 7-31 to 7-32
formatted • 7-32
list-directed• 7-31, 7-32
relationship to DECODE statement• A - 1, A-2
sequential READ• 7-15 to 7-25
formatted• 7-15 , 7-16
list-directed• 7- 15 , 7-17 to 7-19
namelist-directed • 7- 15, 7- 20 to 7-25
unformatted•7-15, 7-25
REAL
See REAL•4
declaring data type• 4-8 to 4-10
REAL• 16
See also Arrays , Constants , Data types,
Variables
constants• 2-12 to 2-13
data type
definition• 2- 1
representation in memory• C-4 , C-7
storage requirements• 2-2 to 2-3
REAL• 16 float intrinsic function• D-38
REAL•4
See also Arrays, Constants, Data types,
Variables
constants• 2-8 to 2-10

REAL•4
data type
definition• 2- 1
representation in memory• C- 4
storage requirements• 2- 2 to 2- 3
default data type of undeclared names• 4-22
REAL•8
See also Arrays , Constants , Data types,
Variables
constants• 2-10 to 2- 12
data type
definition• 2-1
representation in memory (G _ and D_
floating)• C-3 , C-4 , C-5 to C-6
storage requirement• 2-2 to 2-3
D_ floating and G_ fl oating
implementations• 2- 4
REAL •8 float intrinsic function• D- 38
REAL•8 product of REAL•4's fun ction• D- 39
Real editing (F ,E,D,G) • 8- 17 to 8-25
complex data editing• 8-25
relationship to DECODE statement• A-1
REAL intrinsic function• D- 37 , D-39
Real Part of Complex function• D-39
REC
DELETE statement keyword• 9-36
specifier in 1/0 statements• 7-6
RECL
INQUIRE statement specifier• 9-32
OPEN statement keyword• 9- 4 , 9-18
Record and field references• 2-36 to 2-37
examples• 2- 38 to 2-39
Record names
statements that can use• 4-30
Records
allowable operations on aggregate fields• 2-37
arrangement in memory• 2- 33 to 2- 36
defining values of• 3-1
freeing locked records• 9-38
general description• 2-31 to 2- 32
1/0 records
deleting records from a file
(DELETE)• 9-36 to 9-37
RECORDTYPE keyword (INQUIRE
statement) • 9-32
RECORDTYPE keyword (OPEN
statement) • 9-20

lndex-17

Records
1/0 records (cont'd.)
sizes (OPEN statement keywords) • 9-18
RECORDSIZE
OPEN statement keyword• 9-4, 9-20
Record size (RECL)
default va lues• 9-19
limits • 9-19
Record specifier
control list parameter
in 1/0 statements• 7-6
RECORD statement
general description• 4-29 to 4- 30
RECORDTYPE
INQUIRE statement specifier• 9-32
OPEN statement keyword • 9-4 ,
9-20 to 9-21
%REF built-in function• 6-10
References, function
See function references
References, generic or specific
See function references
Relational expressions• 2-48 to 2-49
Relational operators• 2-48
avoiding use as field names• 2-38
in expressions• D-1
Relative organization files
defining size and structure
DEFINE FILE statement• A-3 to A-4
deleting records from
DELETE statement• 9-36 to 9-37
freeing locked records• 9-38
Remainder intrinsic function • D-41
Repeat count
in FORMAT statements• 8-8
Return argument, alternate• 6-9
RETURN statement
general description• 5-25 to 5-27
in parallel DO-loop• 10-4
return args in CALL• 5-25, 5-27
use with FUNCTION statement• 6-15
use with SUBROUTINE statement• 6-18 ,
6-20
REWIND statement
See also BACKSPACE statement
general description• 9-34
REWRITE statements • 7-45 to 7-4 7

18-lndex

Run-time formats• 8-41 to 8-42
Run-time library routines
in parallel DO-loop • 10-4

s
s
edit descriptor• 8-12
SAVE
file disposition• 9-23
SA VE statement
general description • 4-30 to 4-3 1
use of for private entities• 10-7
using unsubscripted array names• 2-29
Scalar field reference
examples• 2-38 to 2-39
format of• 2-36 to 2-37
Scalar memory reference• 2-39 to 2-41
Scalar reference• 2-39 to 2-41
Scale factor editing (P) • 8-25 to 8-2 7
SECNDS function subprogram • D-48
Segmented records
RECORDTYPE keyword (OPEN
statement)• 9-4, 9-20 to 9-21
Separators
external fie ld separators• 8-40 to 8-41
format specification
separators• 8-39 to 8-40
Sequence number field• 1-10, 1-15
SEQUENTIAL
INQUIRE statement specifier• 9-33
OPEN statement keyword value• 9-4
Sequential 1/0 statements
READ statements• 7-15 to 7-25
WRITE statements• 7-33 to 7-39
Sequential organization files
freeing locked records• 9-38
repositioning
REWIND statement• 9- 34
repositioning with BACKSPACE
statement• 9-35
writing end-of-file records
ENDFILE statement• 9-35 to 9-36
'SEQUENTIAL'
OPEN statement keyword value • 9-8
SHARED
OPEN statement keyword• 9-4, 9-21

SHARED directive• 10-7
SHARED_ALL directive• 10-8
Sign control editing • 8-11
SIGN intrinsic function• 0-41
Simple list elements
1/0 list parameter
in 1/0 statements• 7-12
SINO intrinsic function• 0-33
Sine (degree) intrinsic function• 0-33
Sine intrinsic function • 0-33
SINH intrinsic function• 0-35
SIN intrinsic function • 0-33
SIZE OF intrinsic function• D-44
Slash ( /)
division operator• 2-42 to 2-44, 2-51
record terminators
in FORMAT statements • 8-4
Source code
See also source program
allowable characters • 1-9
comments in • 1-7
debugging statements in • 1-14
description of fields • 1-9 to 1-15
format using fixed-format • 1-10 to 1-11
format using tab-format • 1-11 to 1-13
Source listing
of COD records • 1-16
of included files • 1-17
Source program
See also source code
definition of a program unit• 1-2
Din column 1•1-14
statement order• 1-3 to 1- 5
symbolic names in • 1-5 to 1-7
SP
edit descriptor• 8-11
Space character• 1-9
effect of FORMAT descriptors • 8-7, 8-1 O
in statement label fields • 1-13
Special characters• 1-8
Specification statements • 4-1 to 4-42
SORT intrinsic function • 0-33
Square root intrinsic function• 0-33
SS
edit descriptor• 8-11
/ST AND ARD qualifier• 4-31

Standards
See ANSI Standard, FORTRAN-66 ,
FORTRAN-77, ISO Standard
Statement field• 1-10, 1-14
Statement functions• 6-12 to 6-14
Statement label
rules governing use of• 1-13
Statement label field• 1-10, 1-13
Statement label references
FORMAT and GOTO statements • 3-7
symbolic • 3-7 to 3-8
Statement labels
assigning symbols to • 3-7 to 3-8
rules governing use • 1-3
Statement order
following OPTIONS statement • 1-19
requirements of• 1-3t
Statements
See FORTRAN statements
STATUS
CLOSE statement keyword• 9-23
OPEN statement keyword• 9- 4, 9-21
STOP statement
general description• 5-27
in parallel DO-loop • 10-4
Storage allocation, file
OPEN statement keywords
EXTENDSIZE • 9-4, 9-12
INITIALSIZE • 9-4, 9-14
Storage requirements
of data types• 2-3
Storage units
character• 2-2
numeric• 2-2
Stream records
RECORDTYPE keyword (OPEN
statement)• 9-4, 9-20 to 9-21
Structure declaration block
general description• 2-32 to 2-33
Structure declaration blocks
components of• 4-32
data type declaration rules • 4-34
field declarations within• 4-34 to 4-38
general description • 4-31 to 4-4 1
use of %FILL• 2-33, 4-34
Structure declarations• 4-33
STRUCTURE statement
general description • 4-33 to 4-34

lndex-19

Subexpressions
in logical expressions• 2-51
SUBMIT
file disposition• 9-23
Subprogram arguments
aggregate field references used as• 2-37
associating arrays with• 2-25
associating variables with• 2-22
bit function arguments• 0-50 to 0-52
external procedure names used
as• 4-21 to 4-22
general description• 6-2 to 6-11
adjustable arrays• 6-3 to 6-5
alternate return arguments• 6-9
assumed-size arrays• 6-6
character arrays • 6-7
defaults for arguments
passing• 6-9 to 6-11
Hollerith and character constants• 6-8
overview• 6-2
passed-length character arguments• 6- 7
intrinsic function names used as• 4-23
use of built-in functions
argument list functions (%VAL, %REF,
%0ESCR) • 6-9 to 6-11
%LOC function• 6-11
Subprograms
bit functions
general discussion about• 0-50 to 0-52
CHARACTER FUNCTION statement• 6-15
definition of• 1-2
effect of END statement• 5-12
ENTRY statement• 6-21 to 6-24
function references• 6-16 to 6-18
functions, built-in
argument list functions (%VAL, %REF,
%DESCR) • 6-9 to 6-11
%LOC function• 6-11
FUNCTION statement• 6-15 to 6-18
invoking with CALL• 5-2
passed-length character arguments
used in• 2-23
SUBROUTINE statement• 6-18 to 6-2 1
system-supplied FORTRAN intrinsic functions
algorithms used in• D-32
character comparison
functions• 6-30 to 6-32

20-lndex

Subprograms
system-supplied FORTRAN intrinsic functions
(cont 'd .)
complete list of• D-32 to 0-45
description of types• 6-2
duplicating external procedure
names•4-21
lexical comparison
functions• 6-32 to 6-33
references, generic• 6-26 to 6-27,
6-28to 6-30
references, specific• 6-25 ,
6-28to 6-30
system-supplied intrinsic functions
names used as arguments• 4-23
system-supplied subroutines and functions
list and descriptions of• 0-45 to 0-53
use of RETURN statement• 5-25 to 5-27
user-written functions
function subprograms• 6-15 to 6-18
subroutine subprograms• 6-18 to 6-21
user-written subprograms
general description• 6-11 to 6-12
statement functions • 6-12 to 6-14
Subroutine arguments
See subprogram arguments
SUBROUTINE statement• 6-18 to 6-21
see also subprograms
position after OPTIONS statement • 1-19
using unsubscripted array names• 2-29
Subscripts, array• 2-27
Substrings
making equivalent• 4 - 17 to 4-20
Substrings, character
addressing in variables, arrays, and array
elements• 2-30 to 2-31
definition• 2-4
Substructure
example of• 2-35
Substructure declarations
general description• 2-32, 4-32, 4-34, 4 - 38
SUBTITLE directive• 10-13
Subtraction operator (-) • 2-42 to 2-44
Symbolic names
assigning to constants with PARAMETER
statement• 4-26 to 4-28
assigning to main program unit• 4-28 to 4-29

Symbolic names (cont'd.)
default data types• 4-22
external procedure names as subprogram
arguments• 4-21 to 4-22
intrinsic function names used as subprogram
arguments• 4-23
of arrays• 2-25
of constants• 4- 26
rules, conventions, and use• 1-5 to 1-7
use with variables• 2-22
Symbolic statement labels
establishing • 3-7 to 3-8
in formatted 1/0 statements• 3-7 to 3-8
in GOTO statements • 3-7 to 3-8
Symbols
in parallel processing
specifying private default
shareability • 10-3, 10-7
specifying private shareability • 10-3,
10- 6
modifying
shareability in parallel DO-loop•
10-2 to 10-7
System services
calling from parallel DO-loop • 10-4
System time
function subprogram for calculating
SECNDS • D-48
subroutine for calculating
TIME• D-49 to 0-50

T
Tab format • 1-11 to 1-13
Tags
of compiler directives• 10-1
T AND intrinsic function• 0-34
Tangent (degree) intrinsic function• 0-34
Tangent intrinsic function• 0-34
TANH intrinsic function• D-35
TAN intrinsic function• 0-34
T edit descriptor• 8-34, 8-35
Text file libraries
accessing • 1-17 to 1-18
Time, system
See System time • D-48
TIME subroutine• 0-49 to 0-50

TITLE directive• 10-13
TL edit descriptor• 8- 34, 8-36
Transfer, control
See Control transfer
Transfer-of-control specifier
control list parameter
in 1/0 statements• 7-10
Transfer of Sign intrinsic function• D-41
TR edit descriptor• 8- 34 , 8-36
Truncation intrinsic function• 0-36
TYPE
OPEN statement keyword• 9-4, 9-22
Type declaration statement
See Data type declaration statement
to establish variables• 2-22, 2-23
TYPE statement• 7-48 to 7-49

u
Unary operators
definition of• 2-43
Unary plus and minus operators
(+and-)• 2-42 to 2-44, 2-51
Unconditional GO TO statement • 5-1 3
Undeclared symbolic names
default data types• 4 - 22
UNFORMATTED
INQUIRE statement specifier• 9-33
Unformatted 1/0 statements
READ statements
direct access• 7-26 , 7-27
indexed• 7-28, 7-30
sequential• 7-15, 7-25
REWRITE statements • 7-45 , 7-46
use of aggregate field references• 2-37
WRIT!; statements
direct access• 7-39, 7-40
indexed• 7-41 , 7-43
sequential• 7-33, 7-39
Union declarations
contrasted with EQUIVALENCE• 4-40
definition• 4-32
general description• 4-38 to 4-41
UNION statement• 4-39
UNIT
BACKSPACE statement keyword• 9-35
CLOSE statement keyword• 9-23

lndex-21

UNIT (cont'd.)
DELETE statement keyword • 9-36
ENDFILE statement keyword• 9-35
INQUIRE statement keyword• 9-25
OPEN statement keyword• 9-4, 9-22
REWIND statement keyword • 9-34
specifier in 1/0 statements• 7-3
UNLOCK statement keyword • 9-38
UNLOCK statement• 9-38
Unnamed fields
in a structure• 2-33
Unsubscripted array names
usage restrictions• 2-29
use of• 2-29
Uppercase characters • 1-8
effect on compiler• 1-9
in character and Hollerith constants• 1-9
User-defined functions
references to in dimension bounds expressions
•2-26
USEROPEN
OPEN statement keyword• 9-4, 9-23

v
%VAL built-in function• 6-1 O
Variable-length records
RECORDTYPE keyword (OPEN statement) •
9-4, 9-20 to 9-21
Variables
as scalar references• 2-39
association of two or more• 2-22
character substrings• 2- 30 to 2-31
data types of• 2-1
data typing by implication• 2-24
data typing by specification• 2-23
default shareability in parallel
DO-loop• 10-2 to 10-7
defining in memory• 2-22
defining values of• 3-1
definition• 2-4, 2-22
establishing with subprogram references• 2-22
initializing with DAT A statements• 4-5 to 4-8
in structure declarations• 2-32
Variant record capability• 2-33
VAX FORTRAN
extensions to ANSI Standard• 1-1

22-lndax

VIRTUAL statement
DIMENSION statement compared to • 4-13
VOLATILE statement
general description • 4-4 1

w
/WARNINGS qualifier • 4-23
WRITE statements • 7-33 to 7-44
direct access WRITE• 7-39 to 7-40
formatted•7-39, 7-40
unformatted • 7-39, 7-40
indexed WRITE • 7-41 to 7-43
formatted•7-41, 7-42
unformatted • 7-4 1, 7-43
internal WRITE • 7- 43 to 7-44
formatted • 7-43, 7-44
list-directed• 7-43 , 7-44
relationship to ENCODE statement• A-1, A-2
sequential WRITE• 7-33 to 7-39
formatted•7-33, 7-34to 7-35
list-directed• 7-33, 7- 35 to 7-37
namelist-directed • 7-33, 7-37 to 7-38
unformatted• 7-33 , 7-39

x
X edit descriptor• 8-34, 8-34 to 8-35
.XOR.
See logical operators

z
Zero-Extended Functions• D-37
ZEXT intrinsic function• D-37
Z field descriptor• 8-16

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