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Date: Sat, 22 Apr 1995 13:27:45 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199504220327.NAA06522@godzilla.zeta.org.au>
To: hackers@FreeBSD.org, rpt@miles.sso.loral.com
Subject: Re: _ANSI_SOURCE... who defines this puppy
Sender: hackers-owner@FreeBSD.org
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>I am trying to get pthreads to build on 2.0R. I have had a number of 
>problems, but this last one led me down a rat hole that seems to go 
>beyond pthreads. In one source file was :
>    #if !defined(_ANSI_SOURCE)
>    #define CLK_TCK     100  
>    #endif /* not ANSI */

This is bogus.  CLK_TCK is an (obsolescent) POSIX feature.  It has nothing
to do with ANSI C, and of course applications and libraries shouldn't
declare it directly, because it may be (and is in FreeBSD) different
from what the application might expect.

>This resulted in  redefinition of the value in <machine/limits.h>.
>So I started to try to hunt down who defines _ANSI_SOURCE. I found it 
>referenced numerous times in places in the standard includes. But I 
>can't find anywhere that it is defined. The best gcc does is:

><~/code>> cc -E -dM  -ansi foo.c
>#define __STRICT_ANSI__ 1 
>...

>So is this the programmers responsibility to define? 

Yes.  You normally wouldn't want to define it.  In FreeBSD, it is
supposed to restrict what the ANSI headers declare to only those
things that are specified in the standard.  Very few things can
be compiled using only features that are specified in the standard!

__STRICT_ANSI__ is what gcc declares to indicate that the compiler
is enforcing strict ANSI C syntax.  It is not related to restricting
or extending the declarations in the headers.

Bruce