Tru64 UNIX

Compaq C Language Reference Manual

Order Number: AA--RH9NB--TE

April 2000

This document is the language reference manual for Compaq C.

Software Version: Compaq C Version 6.1 for Tru64 UNIX Version 5.0A or higher

Compaq C Version 6.2 for OpenVMS Systems

Compaq C Version 6.2 for Linux Alpha

Compaq Computer Corporation
Houston, Texas

COMPAQ, VAX, and the Compaq logo Registered in U.S. Patent and Trademark Office. Tru64 and OpenVMS are trademarks of Compaq Information Technologies Group, L.P. UNIX is a trademark of The Open Group. All other product names mentioned herein may be trademarks or registered trademarks of their respective companies.

Confidential computer software. Valid license from Compaq required for possession, use, or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor's standard commercial license.

Compaq shall not be liable for technical or editorial errors or omissions contained herein. The information in this publication is subject to change without notice and is provided "as is" without warranty of any kind. The entire risk arising out of the use of this information remains with recipient. In no event shall Compaq be liable for any direct, consequential, incidental, special, punitive, or other damages whatsoever (including without limitation, damages for loss of business profits, business interruption or loss of business information), even if Compaq has been advised of the possibility of such damages. The foregoing shall apply regardless of the negligence or other fault of either party and regardless of whether such liability sounds in contract, negligence, tort, or any other theory of legal liability, and notwithstanding any failure of essential purpose of any limited remedy.

The limited warranties for Compaq products are exclusively set forth in the documentation accompanying such products. Nothing herein should be construed as constituting a further or additional warranty.

Contents Index

Preface

This manual provides reference information for using the Compaq C language on Compaq systems. Compaq C is an ISO/ANSI-compliant C compiler for Compaq OpenVMS^tm VAX^® and Compaq OpenVMS Alpha systems, Compaq Tru64^tm UNIX^® systems, and Linux Alpha systems. Tru64 UNIX runs on Alpha processors.

Compaq has changed the name of its UNIX operating system from DIGITAL UNIX to Tru64 UNIX.

Compaq C is compliant with the International Standards Organization (ISO) C Standard (ISO 9899:1990[1992]), formerly the American National Standard for Information Systems-Programming Language C (document number: X3.159-1989). By the use of command-line options, Compaq C is compatible with older dialects of C, including common usage C (Kernighan and Ritchie C) and VAX C.

This manual is based on the ISO C Standard (ISO 9899:1990[1992]), formerly the ANSI X3J11 committee's standard for the C programming language (called the ANSI C standard in this manual). ¹ All library functions and language extensions to the ANSI C standard are also described.

You may send comments or suggestions regarding this manual or any Compaq C document by sending electronic mail to the following Internet address:

c_docs@zko.dec.com

Note

¹ Compaq would like to thank CBEMA and its Accredited Standards Committee X3 for use of the material derived in whole or in part from the American National Standard Programming Language C. The ANSI C standard may be purchased from the ANSI Sales Department by calling the United States telephone number 1-212-642-4900.

Intended Audience

This manual is intended for programmers who need reference information on the Compaq C (formerly DEC C) language. There is little task-oriented material or platform-specific material in this manual; for that type of information, see your platform-specific Compaq C documentation (user's guide and online help for OpenVMS systems, programmer's guide and manpages for Tru64 UNIX systems.)

Purpose of the ANSI Standard

The ANSI C standard was developed by a committee of program developers and knowledgeable C users to address the problems caused by inexact specification of the C language. These problems were primarily related to portability of programs between different types of machines. The committee analyzed the language for areas where its syntax and semantics were vague or indeterminate, and then chose precise definitions for those C constructs. The result is an unambiguous, machine-independent definition.

The ANSI C standard states that it:

" specifies the form and establishes the interpretation of programs expressed in the programming language C. [The standard's] purpose is to promote portability, reliability, maintainability, and efficient execution of C language programs on a variety of computing systems. "

The standard specifies:

Representation, syntax, and constraints of the C language
Semantic rules for interpreting C programs
Representation of input and output in C programs

The ANSI C standard does not specify:

How C programs are compiled
How C programs are linked
How C programs are executed
All minimum or maximum limits on the size of machines running ANSI C programs

New and Changed Features

This manual was revised for Compaq C Version 6.2 to reflect the following new features. Note that Tru64 UNIX Version 5.0A is shipped with Version 6.1 of the C compiler and, therefore, does not include the listed features, except for the compiler name change.

The name of the product has been changed from DEC C to Compaq C. This change reflects only the acquisiton of the corporation, and meeting the new requirements for product branding. The technical content of the compiler has not changed, and in particular the use of the string DEC or DECC in the software itself (for example, names of predefined macros, command-line qualifiers, filenames, symbol prefixes, and so on) has not changed.
Compound literal expressions are supported ( Section 6.10).
Within a compound statement, declarations and statements can now be freely interspersed in any order ( Section 7.2).
The first clause of a for can be a declaration whose scope includes the remaining clauses of the for header and the entire loop body ( Section 7.6.3).
Support for the __typeof__ operator is added ( Section 6.4.8).
The __align keyword is added Section 2.11.4.
The inline keyword is added as as a declaration specifier in the declaration of a function. ( Section 2.11.2).
The __func__ predeclared identifier is added ( Section 8.9).
Documentation enhancement (OPENVMS ONLY): The Compaq C manuals, help, and release notes are now installed in HTML form in a subdirectory of SYS$HELP. They can be accessed from a locally-running browser through:
file:/sys$common/syshlp/cc$vax_help_062/index.htm
To access these documents from a browser running on a different system, you can copy the entire directory contents to a directory or server system that is accessible to your browser.

Manual Structure

This manual has the following chapters and appendixes:

Chapter 1 describes the elements of the C language.

Chapter 2 discusses some of the basic concepts underlying the C language.

Chapter 3 explains Compaq C data types and type qualifiers.

Chapter 4 describes the declaration of identifiers in Compaq C. The declaration of constants, variables, structures, unions, pointers, and arrays is covered.

Chapter 5 describes function calls, function declarations, function definitions, function parameters, and function arguments.

Chapter 6 discusses the types of expressions you can build in C. It also explains the effects of operators available in C, including unary, binary, conditional, primary, and postfix operators.

Chapter 7 describes the C statements that provide flow control, conditional executions, looping, and interruption.

Chapter 8 explains the purpose of the C preprocessor directives and predefined macros.

Chapter 9 lists and describes the functions, macros, and types in the ANSI C standard library, arranged by header file.

Appendix A provides a syntax summary of all C language constructs.

Appendix B describes the extent of the ANSI conformance of Compaq C, including exceptions and extensions to the standard.

Appendix C provides the ASCII octal, decimal, and hexadecimal equivalents for each character in the ASCII character set.

Appendix D lists the common C extensions supported by Compaq C using the common C compatibility option.

Appendix E lists the VAX C extensions supported by Compaq C using the VAX C compatibility option.

Associated Documents

You may find the following documents useful when programming in Compaq C:

Compaq C User's Guide for OpenVMS Systems---This guide contains the information necessary for developing and debugging Compaq C programs on the OpenVMS operating system. This guide also includes Compaq C features specific to OpenVMS systems, as well as information about porting C programs to and from OpenVMS and other operating systems.
Compaq C Run-Time Library Reference Manual for OpenVMS Systems---Provides complete reference information on the Compaq C library functions included with the OpenVMS operating system.
cc(1) manpage---This manpage describes the cc command line options for Compaq C on Tru64 UNIX systems.

Tru64 UNIX documentation set---This documentation set provides information about the Tru64 UNIX operating system and its utilities. The following volumes are especially useful:

Tru64 UNIX Programmer's Guide---This guide describes the Tru64 UNIX programming environment, including information necessary for developing and debugging C programs on the Tru64 UNIX operating system. This guide, together with the cc(1) manpage, includes Compaq C features specific to Tru64 UNIX systems.
Tru64 UNIX Reference Pages, Sections 2 and 3---Provides complete reference information on the C library functions included with the Tru64 UNIX operating system.

The printed version of the Tru64 UNIX documentation uses letter icons on the spines of the books to help specific audiences quickly find the books that meet their needs. (You can order the printed documentation from Compaq.) The following list describes this convention:

G	Books for general users
S	Books for system and network administrators
P	Books for programmers
D	Books for device driver writers
R	Books for reference page users

Some books in the documentation help meet the needs of several audiences. For example, the information in some system books is also used by programmers. Keep this in mind when searching for information on specific topics.
The Documentation Overview provides information on all of the books in the Tru64 UNIX documentation set.

American National Standard for Information Systems--Programming Language C---This document is the result of the X3J11 standards committee analysis of the C language. This document is a very technical description of the ANSI C language, written for knowledgeable C programmers.
The C Programming Language, 2nd Edition²---This volume was produced before the final ANSI standard was accepted, but it still serves as a valuable reference to the C language.
Because ANSI C contains more features and enhancements to the C language than are defined in The C Programming Language, use this Compaq C Language Reference Manual as the reference for a full description of Compaq C.

Note

² Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language (Englewood Cliffs, New Jersey: Prentice Hall, 1988).

Conventions Used in This Document

Convention Meaning

OpenVMS systems Refers to OpenVMS VAX and OpenVMS Alpha systems unless otherwise specified.

[Return] The symbol [Return] represents a single stroke of the Return key on a terminal.

[Ctrl/X] The symbol [Ctrl/X], where X represents a terminal control character, represents holding down the Ctrl key while pressing the specified terminal character key.

Compaq C also allows ... Compaq C extensions to the ANSI C standard are shown in teal blue in the HTML version of the manual.

float x;
.
.
.
x = 5; A vertical ellipsis indicates that not all of the text of a program or program output is shown. Only relevant material is shown in the example.

option,... A horizontal ellipsis indicates that additional parameters, options, or values can be entered. A comma preceding the ellipsis indicates that successive items must be separated by commas.

syntax _opt Optional syntax elements are indicated with the subscripted abbreviation opt. Isolated syntax diagrams in individual sections of this manual may require reference to Appendix A to determine the complete syntax for a construct. For instance, the ANSI C standard syntax includes a constant as a potential assignment-expression.

storage-class-specifier :
auto
static
register
In syntax definitions, items appearing on separate lines are mutually exclusive alternatives.

The auto storage class...
The fprintf function... Monospaced type identifies language keywords, the names of independently compiled external functions and files, syntax summaries, and references to variables or identifiers introduced in an example.

Convention	Meaning
OpenVMS systems	Refers to OpenVMS VAX and OpenVMS Alpha systems unless otherwise specified.
`[Return]`	The symbol `[Return]` represents a single stroke of the Return key on a terminal.
`[Ctrl/X]`	The symbol `[Ctrl/X]`, where X represents a terminal control character, represents holding down the Ctrl key while pressing the specified terminal character key.
Compaq C also allows ...	Compaq C extensions to the ANSI C standard are shown in teal blue in the HTML version of the manual.
`float x;` . . . `x = 5;`	A vertical ellipsis indicates that not all of the text of a program or program output is shown. Only relevant material is shown in the example.
`option,...`	A horizontal ellipsis indicates that additional parameters, options, or values can be entered. A comma preceding the ellipsis indicates that successive items must be separated by commas.
`syntax _opt`	Optional syntax elements are indicated with the subscripted abbreviation opt. Isolated syntax diagrams in individual sections of this manual may require reference to Appendix A to determine the complete syntax for a construct. For instance, the ANSI C standard syntax includes a constant as a potential assignment-expression.
`storage-class-specifier :` `auto` `static` `register`	In syntax definitions, items appearing on separate lines are mutually exclusive alternatives.
The `auto` storage class... The `fprintf` function...	Monospaced type identifies language keywords, the names of independently compiled external functions and files, syntax summaries, and references to variables or identifiers introduced in an example.

Reader's Comments

Compaq welcomes any comments and suggestions you have on this and other Tru64 UNIX manuals. You can send your comments in the following ways:

Fax: 603-881-0120 Attn: UEG Publications, ZK03-3/Y32
Internet electronic mail: readers_comment@zk3.dec.com
A Reader's Comment form is located online in the following location:
/usr/doc/readers_comment.txt
Mail:
Compaq Computer Corporation
UEG Publications Manager
ZK03-3/Y32
110 Spit Brook Road
Nashua, NH 03062-9987
A Reader's Comments form is located in the back of each printed manual. The form is postage paid, if mailed in the United States.

Please include the following information along with your comments:

The full title of the book and the order number. (The order number is printed on the title page of this book and on its back cover.)
The section numbers and page numbers of the information on which you are commenting.
The version of Tru64 UNIX that you are using. For example, Tru64 UNIX Version 5.0.
If known, the type of processor that is running the Tru64 UNIX software. For example, AlphaServer 2000.

The Tru64 UNIX Publications group cannot respond to system problems or technical support inquiries. Please address technical questions to your local system vendor or to the appropriate Compaq technical support office. Information provided with the software media explains how to send problem reports to Compaq.

Contents

Index