Defining predefined macros for whole translation unit, revisited

[Ryan S. Arnold]

On Wed, Feb 1, 2012 at 3:25 PM, Joseph S. Myers <joseph@codesourcery.com> wrote:
> On Wed, 1 Feb 2012, Roland McGrath wrote:
>
>> It sounds like for libc the only change is moving the __STDC_* definitions
>> from features.h into another file that features.h #include's.  IMHO that is
>> a nice cleanup in its own right, since those definitions are quite unlike
>> the rest of features.h and the purpose for which I first invented it.
>
> Yes, exactly.  For libc it's a simple change that allows getting this bit
> of the standard right (with the larger GCC change, that now would go in
> GCC 4.8), allows getting similar things right for libdfp and other
> libraries implementing various C extensions, and could be used in future
> for better communication of other libc features to the compiler.
>
> Anyone else have views on making this change to libc?

This is useful to me as the libdfp maintainer.

Per ISO/IEC TR 24732, libdfp is one of the components that makes up
the definition of __STDC_DEC_FP__, along with the compiler.  As it
stands this is currently undefined since the compiler can't guarantee
that the library portion is available.

Currently I have customers who can't check for __STDC_DEC_FP__ support
in the toolchain and must use kludges to determine availability of the
TR conforming implementation, and when lacking, fallback to a
non-conforming DFP implementation.

So, being able to complete this piece of the puzzle would be great.

Ryan