The following examples show the different ways you might want to link Compaq C only or Compaq C++ only programs with the Compaq C RTL on OpenVMS VAX systems:

1. Most of the time, you just want to link against the shareable image:

   $ CC/DECC/PREFIX_LIBRARY_ENTRIES=ALL_ENTRIES PROG1 $ LINK PROG1

   
   The linker automatically searches IMAGELIB.OLB to find DECC$SHR.EXE.

2. If you want to use just object libraries (to write privileged code or for ease of distribution, for example), use the /NOSYSSHR qualifier of the LINK command:

   $ CC/DECC/PREFIX_LIBRARY_ENTRIES=ALL_ENTRIES PROG1 $ LINK/NOSYSSHR PROG1, SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=CMA$TIS

   
   Prefixed Compaq C RTL symbol references in the user program are resolved in STARLET.OLB.

3. When compiling with prefixing disabled, in order to use object libraries that provide alternate implementations of C RTL functions, you need to use the DECC*.OLB object libraries. In this case, compile and link as follows:

   $ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ LINK PROG1, MYLIB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY

   
   Unprefixed Compaq C RTL symbol references in the user program are resolved in MYLIB and DECCRTL.OLB. The unprefixed names refrence prefixed names resolved in DECC$SHR.EXE.
   You can link with any valid combination of DECCRTL.OLB, DECCRTLG.OLB, and DECCCURSE.OLB. In this same example, to get G-floating double-precision, floating-point support, you might use the following compile and LINK commands:

   $ CC/DECC/NOPREFIX_LIBRARY_ENTRIES/FLOAT=G_FLOAT PROG1 $ LINK PROG1, MYLIB/LIBRARY, SYS$LIBRARY:DECCRTLG.OLB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY

4. Combining examples 2 and 3, you might want to use just the object libraries (for writing privileged code or for ease of distribution) and use an object library that provides C RTL functions. In this case, compile and link as follows:

   $ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ LINK/NOSYSSHR PROG1, MYLIB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY

You might have programs that combine VAX C and Compaq C (or Compaq C++) code. The following examples show different ways to link such programs with the Compaq C RTL on OpenVMS VAX systems. These examples correspond to the examples in Section 1.3.3.

1. To link against the shareable image, specify the VAXC2DECC.EXE shareable image:

   $ CC/DECC PROG1 $ CC/VAXC PROG2 $ LINK PROG1, PROG2, TT:/OPTIONS SYS$LIBRARY:VAXC2DECC.EXE/SHARE [Ctrl/Z]

   
   Prefixed C RTL calls from PROG1 are resolved in DECC$SHR. Unprefixed C RTL calls from PROG2 are resolved in VAXC2DECC.EXE, which transfers them to DECC$SHR.

2. If you want to use just object libraries (to write privileged code or for ease of distribution, for example), use the /NOSYSSHR qualifier of the LINK command:

   $ CC/DECC PROG1 $ CC/VAXC PROG2 $ LINK/NOSYSSHR PROG1, PROG2, SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=CMA$TIS

   
   All C RTL calls from both PROG1 and PROG2 are resolved in DECCRTL.OLB.

3. When compiling with prefixing disabled, in order to use object libraries that provide alternate implementations of C RTL functions, you need to use the DECC*.OLB object libraries. In this case, compile and link as follows:

   $ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ CC/VAXC PROG2 $ LINK PROG1, PROG2, MYLIB/LIBRARY, - _$SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=CMA$TIS

   
   Unprefixed Compaq C RTL symbol references in the user program are resolved in MYLIB and DECCRTL.OLB.

4. Combining examples 2 and 3, you might want to use just the object libraries (for writing privileged code or for ease of distribution) and use an object library that provides C RTL functions. In this case, compile and link as follows:

   $ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ CC/VAXC PROG2 $ LINK/NOSYSSHR PROG1, PROG2, MYLIB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY /INCL=CMA$TIS

This section applies to programs running on OpenVMS VAX Version 6.0 or higher.

For programs that currently link with the VAX C RTL object libraries using the /NOSYSSHR qualifier, you must specify /INCLUDE=CMA$TIS for the object library. Otherwise, several symbols will be undefined and the resulting image will not execute. In order to add this qualifier, you cannot use the LNK$LIBRARY logicals to link with the VAX C RTL object libraries. You must use a linker options file or list the VAX C RTL object libraries on the command line. For example:

$ LINK/NOSYSSHR PROG1, SYS$LIBRARY:VAXCRTL.OLB/LIBRARY/INCLUDE=CMA$TIS

1.4 Compaq C RTL Function Prototypes and Syntax

After learning how to link object modules and include header files, you must learn how to reference Compaq C functions in your program. The remaining chapters in this manual provide detailed descriptions of the Compaq C RTL functions.

1.4.1 Function Prototypes

In all chapters, the syntax describing each function follows the standard convention for defining a function. This syntax is called a function prototype (or just prototype). The prototype is a compact representation of the order of a function's arguments (if any), the types of the arguments, and the type of the value returned by a function. The use of prototypes is recommended.

If the return value of the function cannot be easily represented by a C data-type keyword, look for a description of the return values in the explanatory text. The prototype descriptions provide insight into the functionality of the function. These descriptions may not describe how to call the function in your source code.

For example, consider the prototype for the feof function:

#include <stdio.h> int feof(FILE *file_ptr);

This syntax shows the following information:

• The feof prototype resides in the <stdio.h> header file. To use feof , you must include this header file. (Declaring Compaq C RTL functions yourself is not recommended.)
• The feof function returns a value of data type int . This prototype indicates the arguments and the return value of feof .
• There is one argument, file_ptr, that is of type "pointer to FILE". FILE is defined in the <stdio.h> header file.

To use feof in a program, include <stdio.h> anywhere before the function call to feof , as in the following example:

#include <stdio.h> /* Include Standard I/O */ main() { FILE *infile; /* Define a file pointer */ . . . /* Call the function feof */ while ( ! feof(infile) ) /* Until EOF reached */ { /* Perform file operations */ . . . } }

1.4.2 Syntax Conventions for Function Prototypes

Since some library functions take a varying number of parameters, syntax descriptions for function prototypes adhere to the following conventions:

• Ellipses (...) are used to indicate a varying number of parameters.
• In cases where the type of a parameter may vary, its type is not shown in the syntax.

Consider the printf syntax description:

#include <stdio.h> int printf(const char *format_specification, ...);

The syntax description for printf shows that you can specify one or more optional parameters. The remaining information about printf parameters is in the description of the function.

1.4.3 UNIX Style File Specifications

The Compaq C RTL functions and macros often manipulate files. One of the major portability problems is the different file specifications used on various systems. Since many C applications are ported to and from UNIX systems, it is convenient for all compilers to be able to read and understand UNIX system file specifications.

The following file specification conversion functions are included in the Compaq C RTL to assist in porting C programs from UNIX systems to OpenVMS systems:

• decc$match_wild
• decc$translate_vms
• decc$fix_time
• decc$to_vms
• decc$from_vms

For more information about the DEC/Shell, see the Guide to VAX DEC/Shell.

The advantage of including these file specification conversion functions in the Compaq C RTL is that you do not have to rewrite C programs containing UNIX system file specifications. Compaq C can translate most valid UNIX system file specifications to OpenVMS file specifications.

Please note the differences between the UNIX system and OpenVMS file specifications, as well as the method used by the RTL to access files. For example, the RTL accepts a valid OpenVMS specification and most valid UNIX file specifications, but the RTL cannot accept a combination of both. Table 1-2 shows the differences between UNIX system and OpenVMS system file specification delimiters.

Table 1-2 UNIX and OpenVMS File Specification Delimiters

Description	OpenVMS System	UNIX System
Node delimiter	::	!/
Device delimiter	:	/
Directory path delimiter	[ ]	/
Subdirectory delimiter	[ . ]	/
File extension delimiter	.	.
File version delimiter	;	Not applicable

For example, Table 1-3 shows the formats of two valid specifications and one invalid specification.

Table 1-3 Valid and Invalid UNIX and OpenVMS File Specifications

System	File Specification	Valid/Invalid
OpenVMS	BEATLE::DBA0:[MCCARTNEY]SONGS.LIS	Valid
UNIX	beatle!/usr1/mccartney/songs.lis	Valid
---	BEATLE::DBA0:[MCCARTNEY.C]/songs.lis	Invalid

When Compaq C translates file specifications, it looks for both OpenVMS and UNIX system file specifications. Consequently, there may be differences between how Compaq C translates UNIX system file specifications and how UNIX systems translate the same UNIX file specification.

For example, if the two methods of file specification are combined, as in Table 1-3, Compaq C RTL can interpret [MCCARTNEY.C]/songs.lis as either [MCCARTNEY]songs.lis or [C]songs.lis. Therefore, when Compaq C encounters a mixed file specification, an error occurs.

UNIX systems use the same delimiter for the device name, the directory names, and the file name. Due to the ambiguity of UNIX file specifications, Compaq C may not translate a valid UNIX system file specification according to your expectations.

For instance, the OpenVMS system equivalent of /bin/today can be either [BIN]TODAY or [BIN.TODAY]. Compaq C can make the correct interpretation only from the files present. If a file specification conforms to UNIX system file name syntax for a single file or directory, it is converted to the equivalent OpenVMS file name if one of the following conditions is true:

• If the specification corresponds to an existing OpenVMS directory, it is converted to that directory name. For example, /dev/dir/sub is converted to DEV:[DIR.SUB] if DEV:[DIR.SUB] exists.
• If the specification corresponds to an existing OpenVMS file name, it is converted to that file name. For example, /dev/dir/file is converted to DEV:[DIR]FILE if DEV:[DIR]FILE exists.
• If the specification corresponds to a nonexistent OpenVMS file name, but the given device and directory exist, it is converted to a file name. For example, /dev/dir/file is converted to DEV:[DIR]FILE if DEV:[DIR] exists.

In the UNIX system environment, you reference files with a numeric file descriptor. Some file descriptors reference Standard I/O devices; some descriptors reference actual files. If the file descriptor belongs to an unopened file, the Compaq C RTL opens the file. Compaq C equates file descriptors with the following OpenVMS logical names:

File Descriptor	OpenVMS Logical	Meaning
0	SYS$INPUT	Standard input
1	SYS$OUTPUT	Standard output
2	SYS$ERROR	Standard error

1.5 Feature-Test Macros for Header-File Control

Feature-test macros provide a means for writing portable programs. They ensure that the Compaq C RTL symbolic names used by a program do not clash with the symbolic names supplied by the implementation.

The Compaq C Run-time Library header files are coded to support the use of a number of feature-test macros. When an application defines a feature-test macro, the Compaq C RTL header files supply the symbols and prototypes defined by that feature-test macro and nothing else. If a program does not define such a macro, the Compaq C RTL header files define symbols without restriction.

The feature-test macros supported by the Compaq C Run-time Library fall into three broad categories for controlling the visibility of symbols in header files according to the following:

• Standards
• Multiple-version support
• Compatibility

The Compaq C Run-time Library implements parts of the following standards:

• X/Open CAE Specification, System Interfaces and Headers, Issue 4, Version 2, also known as XPG4 V2.
• X/Open CAE Specification, System Interfaces and Headers, Issue 4, also known as XPG4.
• Standard for Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Program Interface (API)---Amendment 2: Threads Extension [C Language], also known as POSIX 1003.1c-1995 or IEEE 1003.1c-1995.
• ISO/IEC 9945-2:1993 - Information Technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities, also known as ISO POSIX-2.
• ISO/IEC 9945-1:1990 - Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Programming Interface (API) (C Language), also known as ISO POSIX-1.
• ISO/IEC 9899:1990-1994 - Programming Languages - C, Amendment 1: Integrity, also known as ISO C, Amendment 1.
• ISO/IEC 9899:1990 - Programming Languages - C, also known as ISO C. The normative part is the same as X3.159-1989, American National Standard for Information Systems - Programming Language C, also known as ANSI C.

You can define a feature-test macro to select each standard. You can do this either with a #define preprocessor directive in your C source before the inclusion of any header file, or with the /DEFINE qualifier on the CC command line.

Table 1-4 lists and describes the Compaq C RTL feature-test macros that control standards support.

macro)

Table 1-4 Feature Test Macros - Standards

Macro Name	Standard Selected	Other Standards Implied	Description
_xopen_source_extended	XPG4 V2	XPG4, ISO POSIX-2, ISO POSIX-1, ANSI C	Makes visible XPG4-extended features, including traditional UNIX-based interfaces not previously adopted by X/Open.
_xopen_source	XPG4	ISO POSIX-2, ISO POSIX-1, ANSI C	Makes visible XPG4 standard symbols and causes _posix_c_source to be set to 2 if it is not already defined with a value greater than 2. 1, 2
_posix_c_source ==199506	IEEE 1003.1c-1995	ISO POSIX-2, ISO POSIX-1, ANSI C	Header files defined by ANSI C make visible those symbols required by IEEE 1003.1c-1995.
_posix_c_source == 2	ISO POSIX-2	ISO POSIX-1, ANSI C	Header files defined by ANSI C make visible those symbols required by ISO POSIX-2 plus those required by ISO POSIX-1.
_posix_c_source == 1	ISO POSIX-1	ANSI C	Header files defined by ANSI C make visible those symbols required by ISO POSIX-1.
__stdc_version__ ==199409	ISO C amdt 1	ANSI C	Makes ISO C amendment 1 symbols visible.
_ansi_c_source	ANSI C	---	Makes ANSI C standard symbols visible.

Features not defined by one of the previously named standards are considered Compaq C extensions and are selected by not defining any standards-related, feature-test macros.

If you do not explicitly define feature test macros to control header file definitions, you implicitly include all defined symbols as well as Compaq C extensions.

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