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feature_test_macros.7: Add an example program 

This example program makes it possible to explore what
feature test macros are set depending on the glibc version
and the macros that are explicitly set.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2009-04-03 10:48:24 +13:00
parent 6e047f1692
commit 79a2258619
1 changed files with 106 additions and 0 deletions
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man7/feature_test_macros.7
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@ -464,6 +464,112 @@ These macros have names prefixed by two underscores (e.g.,
Programs should \fInever\fP define these macros directly:
instead, the appropriate feature test macro(s) from the
list above should be employed.
.SH EXAMPLE
The program below can be used to explore how the various
feature test macros are set depending on the glibc version
and what feature test macros are explicitly set.
The following shell session, on a system with glibc 2.10,
shows some examples of what we would see:
.in +4n
.nf
$ \fBcc ftm.c\fP
$ \fB./a.out\fP
_POSIX_SOURCE defined
_POSIX_C_SOURCE defined: 200809L
_BSD_SOURCE defined
_SVID_SOURCE defined
_ATFILE_SOURCE defined
$ \fBcc -D_XOPEN_SOURCE=500 ftm.c\fP
$ \fB./a.out\fP
_POSIX_SOURCE defined
_POSIX_C_SOURCE defined: 199506L
_XOPEN_SOURCE defined: 500
$ \fBcc -D_GNU_SOURCE ftm.c\fP
$ \fB./a.out\fP
_POSIX_SOURCE defined
_POSIX_C_SOURCE defined: 200809L
_ISOC99_SOURCE defined
_XOPEN_SOURCE defined: 700
_XOPEN_SOURCE_EXTENDED defined
_LARGEFILE64_SOURCE defined
_BSD_SOURCE defined
_SVID_SOURCE defined
_ATFILE_SOURCE defined
_GNU_SOURCE defined
.fi
.in
.SS Program source
\&
.nf
/* ftm.c */
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
#ifdef _POSIX_SOURCE
printf("_POSIX_SOURCE defined\\n");
#endif
#ifdef _POSIX_C_SOURCE
printf("_POSIX_C_SOURCE defined: %ldL\\n", (long) _POSIX_C_SOURCE);
#endif
#ifdef _ISOC99_SOURCE
printf("_ISOC99_SOURCE defined\\n");
#endif
#ifdef _XOPEN_SOURCE
printf("_XOPEN_SOURCE defined: %d\\n", _XOPEN_SOURCE);
#endif
#ifdef _XOPEN_SOURCE_EXTENDED
printf("_XOPEN_SOURCE_EXTENDED defined\\n");
#endif
#ifdef _LARGEFILE64_SOURCE
printf("_LARGEFILE64_SOURCE defined\\n");
#endif
#ifdef _FILE_OFFSET_BITS
printf("_FILE_OFFSET_BITS defined: %d\\n", _FILE_OFFSET_BITS);
#endif
#ifdef _BSD_SOURCE
printf("_BSD_SOURCE defined\\n");
#endif
#ifdef _SVID_SOURCE
printf("_SVID_SOURCE defined\\n");
#endif
#ifdef _ATFILE_SOURCE
printf("_ATFILE_SOURCE defined\\n");
#endif
#ifdef _GNU_SOURCE
printf("_GNU_SOURCE defined\\n");
#endif
#ifdef _REENTRANT
printf("_REENTRANT defined\\n");
#endif
#ifdef _THREAD_SAFE
printf("_THREAD_SAFE defined\\n");
#endif
#ifdef _FORTIFY_SOURCE
printf("_FORTIFY_SOURCE defined\\n");
#endif
exit(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.BR libc (7),
.BR standards (7)