Re: AC_LANG_BOOL_COMPILE_TRY(C) fails with OS vendor compilers

[Paul Eggert]

Noah Misch <address@hidden> writes:

> How about this?
>
> 2.1.  Test { int c[(x) ? 1 : -1];  }
> 2.2.  Test { int c[!(x) ? 1 : -1]; }
> 2.3.  If exactly one of 2.1 and 2.2 fails, use result of 2.1.  Else:
> 2.4.  Test { int c = 1/!!(x); }
> 2.5.  Test { int c = 1/!(x);  }
> 2.6.  If exactly one of 2.4 and 2.5 fails, use result of 2.4.  Otherwise,
> AC_MSG_ERROR with suggested switched to place in CFLAGS.
>
> This should cover all the cases we have observed, prevent a (minute) 
> regression
> in the next release, and report the cases it does not handle.

Yes, that sounds like a good strategy for cross-compiles.  For native
compiles, we could bypass all this and simply run a program.


> Another option, should this issue arise again, is to abuse the bit field size
> expression:
>
> struct foo { int bar : (x ? 8 : -8); };
>
> This will probably have the exact same success and failure modes as the array
> size trick, but I'd be interested to see if Sun CC is kinder to it.

It behaves the same as the array size trick, which shouldn't be too
surprising.