Behavior of #error preprocessor directive

[Gordon Burditt]

>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