Which way AC_USE_SYSTEM_EXTENSIONS works ?

[Konstantin Andreev]

Hello.

I am new to autoconf, and I am sorry if dumb question.

Could you explain, how the AC_USE_SYSTEM_EXTENSIONS macro works ? It
looks like the macro blindly defines all known 'extensions' symbols,
regardless of target system.

Say, on my OpenSolaris 10 this macro defines STDC_HEADERS, _ALL_SOURCE,
_GNU_SOURCE and _TANDEM_SOURCE, which aren't used in system headers.

However, many applications, say, libnet, python, ImageMagick uses these
symbols in their development headers.

I could suppose, that if someone uses 'libnet' for development and
AC_USE_SYSTEM_EXTENSIONS as part of configuration, he gets incorrect
'libnet' headers.

So, which idea is behind the AC_USE_SYSTEM_EXTENSIONS macro, and how to
use it ?

Best regards,
--
Konstantin Andreev.