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inconsistentcy in features.h
- To: libc-alpha at sources dot redhat dot com
- Subject: inconsistentcy in features.h
- From: Markus Kuhn <Markus dot Kuhn at cl dot cam dot ac dot uk>
- Date: Wed, 20 Sep 2000 12:58:37 +0100
/usr/include/features.h in the current snapshot says:
/* These are defined by the user (or the compiler)
to specify the desired environment:
__STRICT_ANSI__ ISO Standard C.
_ISOC99_SOURCE Extensions to ISO C89 from ISO C99.
_POSIX_SOURCE IEEE Std 1003.1.
_POSIX_C_SOURCE If ==1, like _POSIX_SOURCE; if >=2 add IEEE Std 1003.2;
if >=199309L, add IEEE Std 1003.1b-1993;
if >=199506L, add IEEE Std 1003.1c-1995
_XOPEN_SOURCE Includes POSIX and XPG things. Set to 500 if
Single Unix conformance is wanted, to 600 for the
upcoming sixth revision.
_XOPEN_SOURCE_EXTENDED XPG things and X/Open Unix extensions.
_LARGEFILE_SOURCE Some more functions for correct standard I/O.
_LARGEFILE64_SOURCE Additional functionality from LFS for large files.
_FILE_OFFSET_BITS=N Select default filesystem interface.
_BSD_SOURCE ISO C, POSIX, and 4.3BSD things.
_SVID_SOURCE ISO C, POSIX, and SVID things.
_GNU_SOURCE All of the above, plus GNU extensions.
_REENTRANT Select additionally reentrant object.
_THREAD_SAFE Same as _REENTRANT, often used by other systems.
The `-ansi' switch to the GNU C compiler defines __STRICT_ANSI__.
If none of these are defined, the default is all but _GNU_SOURCE.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ... */
The last sentence seems to be wrong. What actually happens when none of
these are defined is merely:
/* Always use ISO C things. */
#define __USE_ANSI 1
/* If nothing (other than _GNU_SOURCE) is defined,
define _BSD_SOURCE and _SVID_SOURCE. */
#if (!defined __STRICT_ANSI__ && !defined _ISOC99_SOURCE && \
!defined _POSIX_SOURCE && !defined _POSIX_C_SOURCE && \
!defined _XOPEN_SOURCE && !defined _XOPEN_SOURCE_EXTENDED && \
!defined _BSD_SOURCE && !defined _SVID_SOURCE)
# define _BSD_SOURCE 1
# define _SVID_SOURCE 1
#endif
/* If none of the ANSI/POSIX macros are defined, use POSIX.1 and POSIX.2
(and IEEE Std 1003.1b-1993 unless _XOPEN_SOURCE is defined). */
#if (!defined __STRICT_ANSI__ && !defined _POSIX_SOURCE && \
!defined _POSIX_C_SOURCE)
# define _POSIX_SOURCE 1
# if defined _XOPEN_SOURCE && (_XOPEN_SOURCE - 0) < 500
# define _POSIX_C_SOURCE 2
# else
# define _POSIX_C_SOURCE 199506L
# endif
#endif
In particular I found that, unless I explicitly add
#define _XOPEN_SOURCE
I will not get wcwidth() from <wchar.h> (which is probably not what we
want based on the comment).
Markus
--
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org, WWW: <http://www.cl.cam.ac.uk/~mgk25/>