[Bug libc/10110] Separate __STDC_* predefines from features.h

["jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=10110

--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2010-06-04 14:41:34 UTC ---
Subject: Re:  Separate __STDC_* predefines from features.h

On Tue, 1 Jun 2010, pasky at suse dot cz wrote:

> So this should be now marked as SUSPENDED, waiting for the gcc changes, right?

No, the GCC changes are waiting on glibc maintainer feedback - feedback on 
whether, given what I said, a libc change using a separate header only for 
__STDC_ISO_10646__ would be acceptable, or whether it will be required for 
GCC to extract the __STDC_ISO_10646__ value using fixincludes.  The basic 
GCC mechanism is needed in any case, but glibc maintainer feedback is 
awaited to determine what the next pair of patches should look like.



--- Comment #6 from Joseph Myers <jsm28 at gcc dot gnu.org> 2011-01-08 17:05:10 UTC ---
Similar use cases for the glibc change and compiler feature also apply for some
optional C1X predefines (these are quite like the use case for DFP
implementation).

* Supposing glibc does not initially when supporting C1X implement the optional
<threads.h> (which duplicates facilities already in POSIX, but with different
interfaces), __STDC_NO_THREADS__ should be predefined (for the whole
translation unit), but users should still be able to use an add-on or
third-party implementation of these functions which should be able to cause
this macro to be undefined (for the whole translation unit) when the -I option
pointing to its headers is passed.  And hardcoding knowledge in GCC that a
particular library feature is unsupported seems like a bad idea since it may
not always be unsupported.

* The optional Annex K (formerly TR 24731-1) will presumably also not be
implemented in glibc (in general those functions are of very dubious design and
utility), but again it should be possible for an add-on or separate
implementation to provide implementation of the functions and wrapper headers,
and to cause __STDC_LIB_EXT1__ to be defined when the appropriate -I option is
passed.

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