> One way to avoid this is to #define a feature-test macro like
> _POSIX_SOURCE.  That will prevent the include files defining anything
> that the relevant standard doesn't permit.  This might be a little
> too restrictive for you, though.

Yes; things like POSIX, because they are (as they must be) rather
least-common-demoninator, are usually too weak to do much that's very
useful in.  (It's probably possible to write some useful tools in pure
POSIX, but they will be a very restricted subset of the set of all
useful tools; for example, I think that as soon as you want to do
networking, you have to include headers not specified by POSIX.  Sure,
you can play "find the standard", looking for the standard that
includes enough to do what you want, if it exists.  I note that
_XOPEN_SOURCE has already adopted a versioning scheme that
philosophically matches the _NETBSD_SOURCE notion Ben Harris already
mentioned....)

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