Compaq C

Order Number: AA--PUNZK--TK

This guide describes using the Compaq C compiler on OpenVMS systems. It contains information on Compaq C program development in the OpenVMS environment, Compaq C features specific to OpenVMS systems, and cross-system portability concerns.

Revision/Update Information: This revised guide supersedes the
DEC C User's Guide for OpenVMS Systems (Order No. AA--PUNZJ--TK)

Software Version: Compaq C Version 6.4 for OpenVMS Systems

Compaq Computer Corporation
Houston, Texas

© 2001 Compaq Computer Corporation.

COMPAQ, the Compaq logo, VAX, Alpha, VMS, and OpenVMS are registered in the U.S. Patent and Trademark Office. Tru64 is a trademark of Compaq Information Technologies Group, L.P. in the United States and other countries. Microsoft and Visual C++ are trademarks of Microsoft Corporation. UNIX is a trademark of The Open Group in the United States and other countries. All other product names mentioned herein may be 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 document is provided as is without warranty of any kind and is subject to change without notice. The warranties for Compaq products are set forth in the express limited warranty statements accompanying such products. Nothing herein should be construed as constituting an additional warranty.

This document is available on CD-ROM.

This document was prepared using DECdocument, Version V3.3-1e.

Contents

Index

This guide contains the information necessary for developing and debugging Compaq C (formerly DEC C) programs on the OpenVMS operating system. Compaq C is compliant with the International Standards Organization (ISO) C Standard (ISO 9899:1990[1992]), formerly the American National Standard for Information (ANSI) Systems-Programming Language C (document number: X3.159-1989), called the ANSI C Standard in this guide. Compaq C is an ANSI compliant C compiler for the OpenVMS operating system on VAX and Alpha processors and for the Tru64 UNIX® operating system on Alpha processors. Through use of command-line options, Compaq C is compatible with older dialects of C, including common usage C and VAX C.

This guide also includes Compaq C language features specific to OpenVMS systems, as well as information about porting C programs to and from OpenVMS and other operating systems. For more information about porting programs to and from other operating systems, see the Compaq C Run-Time Library Reference Manual for OpenVMS Systems.

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

c_docs@compaq.com

Intended Audience

This guide is intended for experienced programmers who need to develop Compaq C programs on OpenVMS systems, for users who need to know the difference between Compaq C and other implementations, and for experienced C users who need to reference language information specific to OpenVMS systems. You should be familiar with one high-level language and should have some familiarity with the DIGITAL Command Language (DCL). If you are not familiar with or need to reference information about the DCL, see Chapter 1.

Document Structure

This guide has the following chapters and appendixes:

• Chapter 1 shows how to create, compile, link, and run a Compaq C program.
• Chapter 2 describes VAX Record Management Services (RMS).
• Chapter 3 describes interlanguage calling, and OpenVMS System Services, Run-Time Library (RTL) routines, and calling standard conventions.
• Chapter 4 describes data storage and representation on OpenVMS systems.
• Chapter 5 describes the preprocessor directives.
• Chapter 6 describes the predefined macros and the built-in functions.
• Appendix A documents the features that distinguish Compaq C for OpenVMS Systems from VAX C Version 3.2.
• Appendix B describes common pitfalls when using Compaq C.
• Appendix C provides an overview of the OpenVMS Debugger, the DIGITAL Text Processing Utility (TPU), the DIGITAL Language-Sensitive Editor (LSE), the DIGITAL Source Code Analyzer (SCA), and CDD/Repository.
• Appendix D lists Compaq C compiler messages.
• Appendix E describes implementation-specific limits and parameters for Compaq C on OpenVMS systems.
• The glossary provides an alphabetical listing of key terms.

Associated Documents

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

• DEC C Migration Guide for OpenVMS VAX Systems---To help OpenVMS VAX application programmers migrate from VAX C to Compaq C. (VAX ONLY)
• Compaq C Installation Guide for OpenVMS VAX Systems---For OpenVMS system programmers who install the Compaq C software on VAX systems. (VAX ONLY)
• Compaq C Installation Guide for OpenVMS Alpha Systems---For OpenVMS system programmers who install the Compaq C software on Alpha systems. (ALPHA ONLY)
• Compaq C Language Reference Manual---Provides language reference information for Compaq C on DIGITAL systems.
• Compaq C Run-Time Library Reference Manual for OpenVMS Systems---Provides information on using the Compaq C Run-Time Library (RTL) functions and macros, and information about porting programs to and from other operating systems.
• The C Programming Language¹---Provides an excellent tutorial of the C language. Because Compaq C contains features and enhancements to the ANSI C language, use the Compaq C User's Guide for OpenVMS Systems and the Compaq C Language Reference Manual as the reference books for the full description of Compaq C.
• OpenVMS Calling Standard---Describes the concepts used by all OpenVMS languages to invoke routines and pass data between them. It also describes the differences between the VAX and Alpha parameter-passing mechanisms.

Conventions Used in this Document

Table 1 lists the conventions used in this guide.

Table 1 Conventions Used in this Guide

Convention	Meaning
[Return]	The symbol [Return] represents a single stroke of the Return key on a terminal.
Ctrl/X	The symbol Ctrl/X, where the letter X represents a terminal control character, is generated by holding down the Ctrl key while pressing the key of the specified terminal character.
switch statement fprintf function auto storage class	In syntax definitions, items appearing in monospaced type identify language keywords and the names of OpenVMS and Compaq C Run-Time Library functions.
arg1	Italic type indicates a placeholder, such as an argument or parameter name, and the introduction of new terms.
$ RUN CPROG [Return]	Interactive examples show user input in boldface type.
float x; . . . x = 5;	A vertical ellipsis indicates that not all of the text of a program or program output is illustrated. Only relevant material is shown in the example.
option,...	A horizontal ellipsis indicates that additional parameters, options, or values can be entered. A comma that precedes the ellipsis indicates that successive items must be separated by commas.
[output-source,...]	Square brackets, in function synopses and a few other contexts, indicate that a syntactic element is optional. Square brackets are not optional, however, when used to delimit a directory name in an OpenVMS file specification or when used to delimit the dimensions of an array in Compaq C source code.
sc-specifier ::= auto static [extern] register	In syntax definitions, items appearing on separate lines are mutually exclusive alternatives.
{a|b}	Braces surrounding two or more items separated by a vertical bar (|) indicate a choice; you must choose one of the two syntactic elements.
<ucDelta symbol>	A delta symbol is used in some contexts to indicate a single ASCII space character.

Platform Labels

A platform is a combination of operating system and hardware that provides a distinct environment. This guide contains information applicable to the OpenVMS operating system on both the VAX and Alpha architectures.

The information in this guide applies to both of these platforms, except when specifically labeled, as follows:

Label	Explanation
(ALPHA ONLY)	Specific to an Alpha processor running the OpenVMS operating system.
(VAX ONLY)	Specific to a VAX processor running the OpenVMS operating system.

New and Changed Features

Compaq C Version 6.4 provides most of the language-feature support for the new C99 standard (ISO/IEC 9899:1999 published by ISO in December, 1999 and adopted as an ANSI standard in April, 2000). See the Compaq C Language Reference Manual for more information on these language features.

This version also adds new command-line options and pragmas, and a new version of the GEM optimizing back end for Alpha systems.

Specific new features of this release include:

• The /STANDARD=C99 qualifier is added for strict ISO C99 standard conformance. This compiler mode accepts just the C99 language without extensions, and diagnoses violations of the C99 standard ( Section 1.3.2).
  The compiler's default language mode remains /STANDARD=RELAXED_ANSI89, which accepts nearly all language extensions as well as standard C89 and C99 features. It excludes only K&R ("common" mode), VAX C, and Microsoft features that conflict with standard C.
  Note: /STANDARD=C99 is not fully supported on OpenVMS VAX systems. Specifying /STANDARD=C99 on OpenVMS VAX systems produces a warning and puts the compiler into /STANDARD=RELAXED_ANSI89 mode.
• C99_ENTRIES to the /PREFIX_LIBRARY_ENTRIES qualifier is added ( Section 1.3.4). (ALPHA ONLY)
  This enables DECC$ prefixing of all those external names that are specified in C99 (a superset of the external names prefixed under /PREFIX=ANSI_C89_ENTRIES and a subset of those prefixed under /PREFIX=ALL_ENTRIES).
  But note that, as previously stated, new C99 run-time library functions will not be available until OpenVMS Alpha releases after Version 7.3.
• The command-line qualifier /FIRST_INCLUDE is added ( Section 1.3.4). (ALPHA ONLY)
• Three new message groups are added ( Section 5.4.12.1):

  NOC89 - features not in C89
  NOC99 - features not in C99
  NEWC99 - features that are new in C99

  
  The existing group, NOANSI is retained as a synonym for NOC89.
• The #pragma names preprocessor directive is added ( Section 5.4.14).
• New #pragma unroll added to control the amount of loop unrolling performed on a subsequent for loop ( Section 5.4.20). (ALPHA ONLY)
• Change is made to the #pragma optimize preprocessor directive. It is no longer controlled by #pragma environment . But it has a new keyword, command_line , which causes the optimization settings to revert to what was in effect at the start of the compilation, as specified by the CC command-line qualifiers ( Section 5.4.15).
• New " _m " suffixed pragma names added to force pragmas to expand macros ( Section 5.4).
• New non_zero keyword for #pragma assert added ( Section 5.4.1.4).
• The long long int type, implemented as an extension on Compaq C several releases ago, is now standardized by C99. This has an effect on how the compiler assigns type to integer constants (ALPHA ONLY). (See the Compaq C Language Reference Manual.)
• The _Pragma operator is added. (See the Compaq C Language Reference Manual.)
• New predefined macros are added:

  __STDC_HOSTED__ (defined with the value 1)
  __STDC_VERSION__ (defined with the value 199901L)
  __STDC_ISO_10646 (defined with the value 199712L)

  
  See the Compaq C Language Reference Manual.
• The static keyword can now be used in array bounds. (See the Compaq C Language Reference Manual.)
• New C99 header file <stdbool.h> and type _Bool is added. This is the C99-specified boolean type. It is not recognized in VAXC, COMMON, or the strict ANSI89 mode. (See the Compaq C Language Reference Manual.)
• New C99 header <complex.h> and type _Complex is added (ALPHA ONLY). (See the Compaq C Language Reference Manual.)
  Note: The run-time support for complex arithmetic will not be available until an OpenVMS release following Version 7.3.
• C99 specifies a new _Imaginary type. (See the Compaq C Language Reference Manual.)
  In Compaq C, use of the _Imaginary keyword produces a warning, which is resolved by treating it as an ordinary identifier.
• New C99 header file <tgmath.h> is added. (See the Compaq C Language Reference Manual.)
• enum declarations now permit a trailing comma at the end of the enumerator-list. (See the Compaq C Language Reference Manual.)
• Support is added for macros with variable-length lists ( __VA_ARGS__ ) and syntax forms with .... (See the Compaq C Language Reference Manual.)

This chapter describes the following information about developing Compaq C programs on an OpenVMS system:

• Overview of the DIGITAL Command Language (DCL) commands used for program development ( Section 1.1)
• Creating Compaq C programs ( Section 1.2)
• Compiling Compaq C programs ( Section 1.3)
• Linking Compaq C programs ( Section 1.4)
• Running Compaq C programs ( Section 1.5)
• Passing arguments to the main function ( Section 1.6)
• Using 64-bit addressing ( Section 1.7)

This section provides a brief overview of the DCL commands used for program development. The following sections provide more detailed information about these topics.

Figure 1-1 shows the basic steps in Compaq C program development.

Figure 1-1 DCL Commands for Developing Programs

To create a Compaq C source program at DCL level, you must invoke a text editor. In Figure 1-1, the EDIT command invokes the default editor EDT to create the source program AVERAGE.C. You can use another editor, such as the OpenVMS Text Processing Utility (TPU) or the Compaq Language-Sensitive Editor (LSE). (LSE is a product that must be purchased separately; see Appendix C for more information.) A file type of C is used to indicate that you are creating a Compaq C source program. C is the conventional file type for all Compaq C source programs.

When you compile your program with the CC command, you do not have to specify the file type; by default, Compaq C searches for files with a file type of C.

If your source program compiles successfully, the Compaq C compiler creates an object file with the file type OBJ.

However, if the Compaq C compiler detects errors in your source program, the system displays each error on your screen and then displays the DCL prompt. You can then reinvoke your text editor to correct each error.

You can specify command qualifiers on the CC command. Command qualifiers cause the Compaq C compiler to perform additional actions. In the following example, the /LIST qualifier causes the Compaq C compiler to produce the listing file AVERAGE.LIS:

$ CC/LIST AVERAGE

For a complete description of all CC command qualifiers, see Section 1.3.4.

After your program has compiled successfully, invoke the OpenVMS Linker to create an executable image file. For example:

$ LINK AVERAGE

The linker uses the object file produced by Compaq C as input to produce an executable image file as output. (The executable image is a file containing program code that can be run on the system.)

You can specify command qualifiers with the DCL command LINK. For a complete list and explanation of all the command qualifiers available with the LINK command, see Section 1.4.2.

After producing the executable image file, use the RUN command to execute your program.

1.2 Creating a Compaq C Program

To create and modify a Compaq C program, you must invoke a text editor. The OpenVMS system provides you with two text editors: EDT and the OpenVMS Text Processing Utility (TPU). The following section discusses TPU. See the OpenVMS EDT Reference Manual for more information on EDT.

1.2.1 Using TPU

TPU is a high-performance, programmable utility. It provides two editing interfaces: the Extensible VAX Editor (EVE), described in the following section, and the TPU EDT Keypad Emulator. You can also create your own interfaces.

Like EDT, TPU provides you with an online help facility that you can access during your editing session. When you invoke TPU to create a file, a journal file is automatically created. You can use this journal file to recover your edits if the system fails during an editing session. To recover your edits, enter the EVE/RECOVER command.

Unlike EDT, TPU provides multiple windows. This feature allows you to view two files on your screen at the same time.

1.2.2 The EVE Interface to TPU

EVE is an interactive text editor that allows you to execute common editing functions using the EVE keypad or to execute more advanced functions by entering commands on the EVE command line. The following command line invokes the EVE editor and creates the file PROG_1.C:

$ EDIT/TPU PROG_1.C

You can define a global symbol for the EDIT/TPU command by placing a symbol definition in your LOGIN.COM file. For example:

$ EVE == "EDIT/TPU"

After this command line is executed, you can type EVE at the DCL prompt followed by the name of the file you want to modify or create.

For more information on using EVE, see the Guide to VMS Text Processing.

1.3 Compiling a Compaq C Program

The Compaq C compiler performs the following functions:

• Detects errors in your source program
• Displays each error on your screen or writes the errors to a file
• Generates machine-language instructions from the source
  statements
• Groups these machine-language instructions into an object module for the linker

The following sections discuss the CC command and its qualifiers.

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