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Re: AC_LANG_BOOL_COMPILE_TRY(C) fails with OS vendor compilers

From: Olaf Weber
Subject: Re: AC_LANG_BOOL_COMPILE_TRY(C) fails with OS vendor compilers
Date: Fri, 02 Jul 2004 16:59:55 +0200
User-agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Security Through Obscurity, linux)

Paul Eggert writes:
> Noah Misch <address@hidden> writes:

>> That said, I'd like to fix it.  Would one of the following be
>> appropriate?
>> 1) Change the test such that it creates truly invalid C in the
>>    false case.  I don't know how to do this, but perhaps a reader
>>    does.  Ideas?

> Unfortunately there's no such thing as "truly invalid C", in the sense
> that every possible C compiler, whether conforming or not, will exit
> with nonzero status when asked to compile it.  This is because people
> are free to add extensions.  The best we can do is to write code that
> fails on all practical implementations.

Perhaps I'm missing the obvious, but why wouldn't something like this

        int array[!!(x)*2-1];

The !! forces (constant) expression 'x' into the range 0-1, and then
we get either 'int array[-1];' or 'int array[1];' as the final result.

Olaf Weber

               (This space left blank for technical reasons.)

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