[Bug libc/15720] stdc-predef.h wrongly defines __STDC_IEC_559_COMPLEX__

["joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15720

--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Sun, 7 Jul 2013, bugdal at aerifal dot cx wrote:

> > Not much good.  You can't use __STDC_VERSION__ in practice to tell what 
> > level of C11 features is supported,
> 
> Combined with the other new __STDC_NO_*__ macros introduced in C11,
> you should be able to determine which features are available.

No, because the set of macros for optional features doesn't correspond at 
all to the various subsets of C11 features that may or may not be 
implemented in compilers' C11 modes.  Wait five or ten years and C11 modes 
may be more reliably more complete.  Your "should" is only for 
applications known to be compiled only with compilers and libraries 
documented to conform in the relevant ways, not for real-world partial C11 
support.

> > can't use __STDC__ to tell if trigraphs are supported,
> 
> This is a bug in GCC, but anybody using trigraphs intentionally or
> otherwise should just be taken out back anyway...

It's a deliberate choice dating back (and documented) to GCC 2.0 at least 
that __STDC__ does not reflect whether a strict conformance mode is 
selected.

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