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From: gordon@sneaky.UUCP (Gordon Burditt)
Newsgroups: comp.lang.c
Subject: Re: Behavior of #error preprocessor directive
Keywords: preprocessor directives ANSI standard
Message-ID: <46106@sneaky.UUCP>
Date: 11 Jan 91 22:58:55 GMT
References: <1192@van-bc.wimsey.bc.ca> <14792@smoke.brl.mil>
Organization: Gordon Burditt
Lines: 21

>Note that code intended to be compiled (with appropriate conditionalizing)
>by both ANSI and pre-ANSI compilers should not use #error, because many
>pre-ANSI C preprocessors would terminate fatally upon seeing #error, even
>in #ifed-out source code.  Thus I tend to still use the kludge
>	#if SOME_EXPR
>	#include "*** ERROR -- SOME_EXPR ***"
>	#endif
>which has a more drastic effect than #error anyway.

This is one place where trigraphs can be useful:

#if SOME_EXPR
??=error "*** ERROR -- SOME_EXPR ***"
#endif /* SOME_EXPR */

If it's an ANSI compiler, it recognizes the second line as #error.
If it's not an ANSI compiler, it probably doesn't recognize ??= as a
trigraph, and will call it an error instead.

						Gordon L. Burditt
						sneaky.lonestar.org!gordon