Developing Applications for Use with UNIX System Services OS/390

Compiling POSIX Programs

The posix compiler option modifies compiler behavior in order to establish certain defaults required by the POSIX.1 standard. A program compiled without the posix option may not behave completely according to the standard even if the program's code is completely conforming.

Some of the effects of the posix option are:

The feature test macro _SASC_POSIX_SOURCE is automatically defined.
The refdef option is assumed.
The special POSIX variable names environ and tzname are made automatically __rent unless explicitly declared __norent .
A run-time flag is set defining the object module as POSIX-compiled.

When a load module containing a main function is link-edited, the resulting load module is considered to be POSIX compiled if any constituent object module was compiled with the posix option. (For this reason, if you are writing routines that may be used in both POSIX and non-POSIX programs, you should not compile them with the posix option, because this would force any load modules that use them to be considered POSIX.)

If the main load module of a program is defined as POSIX compiled, certain library defaults are changed in order to bring them into conformance with the POSIX standard. For instance, in a program that is not POSIX compiled, the function call fopen("sysin", "r") opens the file associated with the DDname SYSIN. In a POSIX compiled program, this call opens the USS HFS file "sysin" in the current directory.

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