This is the complete rework of the feature tests macros for better
compatibility with GNU libc, primarily based on the Linux man pages
documentation:
http://man7.org/linux/man-pages/man7/feature_test_macros.7.html
The previous implementation was flawed in its approach that macros were
often used to hide symbols if defined (e.g. !defined __STRICT_ANSI__ or
!defined _POSIX_SOURCE), whereas the approach of glibc is that these macros
make symbols available when defined (e.g. defined _BSD_SOURCE, or as used
internally, #if __BSD_VISIBLE). As much open-source software is written
with glibc in mind, this necessitated patching numerous packages just to
compile.
In particular, __STRICT_ANSI__ (which is defined by gcc -ansi or -std=c*)
was given too much importance. This implementation limits the influence
of __STRICT_ANSI__ to controlling the default when no other feature test
macros are defined, and to the inclusion of <alloca.h> in <stdlib.h> as
documented. These are the only places where __STRICT_ANSI__ should be
tested.
The following macros are now accepted: _ATFILE_SOURCE, _BSD_SOURCE,
_DEFAULT_SOURCE, _ISOC99_SOURCE, _ISOC11_SOURCE, _LARGEFILE_SOURCE,
_SVID_SOURCE, _XOPEN_SOURCE_EXTENDED.
The existing __*_VISIBLE internal macros have been kept mostly
compatible with the original BSD implementation, with some changes to
the criteria which controls them. Several more macros in this style
have been added where needed for concision or accuracy.
Enabling C++11 or newer in the compiler also enables C99 and C11
functions. Doing so should help move away from the need to define
_GNU_SOURCE in g++ for _GLIBCXX_USE_C99 support as on Linux:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51749
Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>
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