Re: _GNU_SOURCE, _BSD_SOURCE, and __FAVOR_BSD

[Jonathan Nieder <jrnieder at gmail dot com>]

Hi,

Mikel Ward wrote:

> If you want to get the full effect of _GNU_SOURCE but make the BSD
> definitions take precedence over the POSIX definitions, use this
> sequence of definitions:
>
>           #define _GNU_SOURCE
>           #define _BSD_SOURCE
>           #define _SVID_SOURCE
>
> But AFAICT, the order is unimportant.

Yes, the order is unimportant.  I think "sequence" is being used as a
rough synonym for "set".

> I was not relying on any difference, but was wondering what the best
> include order was for portability, and whether the documentation is
> correct.

For maximal portability to current platforms, one should use the POSIX
definitions and define _XOPEN_SOURCE. ;-)  Defining _GNU_SOURCE,
_ALL_SOURCE, _BSD_SOURCE, _SGI_SOURCE, _XOPEN_SOURCE_EXTENDED, etc
tends to also be a good idea, since sometimes (out of date or broken)
C libraries will leave out a definition or two when certain feature
test macros are missing.

Hope that helps,
Jonathan