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5.12 Posix Variants

The following macros check for certain operating systems that need special treatment for some programs, due to exceptional oddities in their header files or libraries. These macros are warts; they will be replaced by a more systematic approach, based on the functions they make available or the environments they provide.

— Macro: AC_AIX

If on AIX, define _ALL_SOURCE. Allows the use of some BSD functions. Should be called before any macros that run the C compiler.

— Macro: AC_GNU_SOURCE

If using the GNU C library, define _GNU_SOURCE. Allows the use of some GNU functions. Should be called before any macros that run the C compiler.

— Macro: AC_ISC_POSIX

For interactive Systems Corporation Unix, add -lcposix to output variable LIBS if necessary for Posix facilities. Call this after AC_PROG_CC and before any other macros that use Posix interfaces. interactive Unix is no longer sold, and Sun says that they will drop support for it on 2006-07-23, so this macro is becoming obsolescent.

— Macro: AC_MINIX

If on Minix, define _MINIX and _POSIX_SOURCE and define _POSIX_1_SOURCE to be 2. This allows the use of Posix facilities. Should be called before any macros that run the C compiler.

— Macro: AC_USE_SYSTEM_EXTENSIONS

If possible, enable extensions to Posix on hosts that normally disable the extensions, typically due to standards-conformance namespace issues. This may involve defining __EXTENSIONS__ and _POSIX_PTHREAD_SEMANTICS, which are macros used by Solaris. This macro also has the combined effects of AC_GNU_SOURCE, AC_AIX, and AC_MINIX.