Guide to VAXC

This document, "Guide to VAX C" (Order No. AI-L370C-TE, March 1987) by Digital Equipment Corporation, provides comprehensive information for programmers developing and debugging VAX C programs in the VMS (Version 4.2 or higher) and MicroVMS environments. It aims to serve as a reference for experienced programmers, detailing the VAX C programming language, its development within the VMS ecosystem, and considerations for cross-system portability.

The guide is structured into three main parts:

1. Developing VAX C Programs on VMS: Covers the practical steps of creating, compiling, linking, and running VAX C programs using Digital Command Language (DCL) commands, along with an introduction to using the VMS Debugger.
2. VAX C Programming Concepts: Explains fundamental C language constructs as implemented in VAX C, including program structure, statements, expressions, operators, data types, declarations, storage classes, allocation, and preprocessor directives.
3. Using VAX C Features on VMS: Delves into VMS-specific functionalities, such as utilizing VAX Record Management Services (RMS) for file handling and integrating VAX C subprograms with other VAX languages within the Common Language Environment.

Key new and changed features highlighted in VAX C Version 2.3 (which this revised document supersedes previous versions):

• Support for VAX Source Code Analyzer (VAXSCA).
• Incompatibility between modules compiled with VAX C V1.n and V2.n compilers, requiring re-compilation.
• The VAX C Run-Time Library (RTL) is now distributed with the VMS Run-Time Library.
• Introduction of function prototypes for argument type checking and conversion during function declarations and calls.
• Discouragement of using the underscore as the first character in program identifiers due to its reserved use for implementation-specific elements.
• Changes to floating-point arithmetic, allowing VAX C to use the precision of the operand when /PRECISION=SINGLE is specified, rather than always double precision.
• Support for volatile and const data type specifiers.
• Support for the /INCLUDE_DIRECTORY qualifier for user-defined include files.
• Support for variant structure and union declarations and vacuous tag declarations.
• Addition of hexadecimal characters in escape sequences and _align for data alignment.
• New preprocessor directives: #pragma and #elif, and the defined operator in #if directives.
• Inclusion of predefined macros like __DATE__, __FILE__, __LINE__, and __TIME__.
• Allowance for macro substitution within #include preprocessor directives.
• Addition of new library files, limits.h and float.h, and enhanced diagnostic messages.