Determining system type

[Doug Gwyn]

In article <15406 at cup.portal.com> gregh at cup.portal.com (Greg S Hinton) writes:
>Is there a "standard" -- or optimal -- way to determine at compile time
>whether one is on a BSD or AT&T (Ver7, SysIII, SysV) system?
>This is the best I've been able to come up with so far:
>#include <stat.h>
>#if defined(S_ISOCK)

You could also test what <sgtty.h> defines.

The real problem is that you're assuming that there are well-defined,
"pure" BSD vs. AT&T environments.  In practice, vendors have grafted
some bits of other systems into their implementations.  This will
reach its zenith with UNIX System V Release 4.  Instead of trying to
conditionalize on "system type", consider tailoring for the exact
features you're interested in; this often requires adding -Ds to
CFLAGS in the Makefile to set the appropriate "feature test macros".
Another viable solution is to isolate all system dependencies in
separate modules, compiling whichever module is appropriate.