Preface

This manual provides reference information for using the DEC C language on Digital systems. DEC C is an ISO/ANSI-compliant C compiler for OpenVMS VAX and Alpha systems and Digital UNIX[R] systems. Digital UNIX runs on Alpha processors.

Digital has changed the name of its UNIX operating system from DEC OSF/1 to Digital UNIX. The new name reflects Digital's commitment to UNIX and its conformance to UNIX standards.

DEC 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, DEC 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 DEC C document by filling out one of the Reader's Comments forms at the back of this manual or by sending electronic mail to the following Internet address:

decc_docs@bookie.enet.dec.com

[1] Digital 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 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 DEC C documentation (user's guide and online help for OpenVMS systems, programmer's guide and manpages for Digital 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

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 DEC C data types and type qualifiers.

Chapter 4 describes the declaration of identifiers in DEC 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 Digital's ANSI conformance, 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 DEC C using the common C compatibility option.

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

Associated Documents

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

• DEC C User's Guide for OpenVMS Systems-This guide contains the information necessary for developing and debugging DEC C programs on the OpenVMS operating system. This guide also includes DEC C features specific to OpenVMS systems, as well as information about porting C programs to and from OpenVMS and other operating systems.

• DEC C Run-Time Library Reference Manual for OpenVMS Systems-Provides complete reference information on the DEC C library functions included with the OpenVMS operating system.

• cc(1) manpage-This manpage describes the cc command line options for DEC C on Digital UNIX systems.

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

  • Digital UNIX Programmer's Guide-This guide describes the Digital UNIX programming environment, including information necessary for developing and debugging C programs on the Digital UNIX operating system. This guide, together with the cc(1) manpage, includes DEC C features specific to Digital UNIX systems.

  • Digital UNIX Reference Pages, Sections 2 and 3-Provides complete reference information on the C library functions included with the Digital UNIX operating system.

• 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 Edition[2]-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 DEC C Language Reference Manual as the reference for a full description of DEC C.

The printed version of the Digital UNIX documentation set is color coded to help specific audiences quickly find the books that meet their needs. (You can order the printed documentation from Digital.) This color coding is reinforced with the use of an icon on the spines of books. The following list describes this convention:

Audience	Icon	Color Code
General users	G	Blue
System and network administrators	S	Red
Programmers	P	Purple
Device driver writers	D	Orange
Reference page users	R	Green

Some books in the Digital UNIX documentation set 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, Glossary, and Master Index provides information on all of the books in the Digital UNIX documentation set.

[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.
DEC C also allows ...	DEC C extensions to the ANSI C standard are shown in teal blue.
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.

New and Changed Features

This manual was revised for DEC C Version 5.6 to reflect DEC C support for the __restrict data type qualifier on pointer declarations. See Section 3.7.4 for more information on restricted pointers.