Tru64 UNIX

This document is the Compaq C Language Reference Manual, published in September 2002 by Hewlett-Packard Company (Hewlett-Packard Company). It serves as a comprehensive reference for using the Compaq C language on HP systems, specifically targeting OpenVMS VAX, OpenVMS Alpha, and Tru64 UNIX platforms (Compaq C for Tru64 UNIX Version 5.1B or higher, Compaq C Version 6.5 for OpenVMS Systems).

The manual details Compaq C's compliance with the ISO C Standard (ISO 9899:1990[1992] / ANSI X3.159-1989), while also noting its compatibility with older C dialects like Kernighan and Ritchie C and VAX C through command-line options. It provides descriptions of all standard library functions and language extensions.

Key topics covered include:

• The C language lexicon (character sets, identifiers, keywords, operators, constants, string literals, comments).
• Basic C concepts (blocks, compilation units, scope, visibility, side effects, linkage, storage classes).
• Data types (integral, floating-point, derived, enumerated, and type qualifiers like const, volatile, __unaligned, __restrict).
• Declarations, initializers, functions, expressions, and statements for flow control.
• Preprocessor directives and predefined macros.
• A comprehensive overview of the ANSI C standard library functions and types.

The September 2002 revision incorporates new C99 language features such as:

• C99 constants for Infinity and NaN (for IEEE floating-point and specific language modes).
• C99 adjacent-string concatenation.
• Universal Character Names (UCNs) in identifiers, string literals, and character constants.
• The C99 _Pragma operator for macro expansion of #pragma directives.
• New #pragma extern_prefix keywords: NOCRTL and RESTORE_CRTL.

The manual is intended for programmers seeking detailed reference information on the Compaq C language and its implementation-specific characteristics.