is there any effective distinction between XPG and XPG XSI?

["Robert P. J. Day" <rpjday-L09J2beyid0N/H6P543EQg@public.gmane.org>]

  last quibble for the day ... perusing the feature test macros
related to XPG and XPG XSI in features.h, starting with the comment:

   _XOPEN_SOURCE        Includes POSIX and XPG things.  Set to 500 if
                        Single Unix conformance is wanted, to 600 for the
                        sixth revision, to 700 for the seventh revision.

ok, fair enough, and if we read further, we see the explanation of the
associated __USE macros:

   __USE_XOPEN2K        Define XPG6 things.
   __USE_XOPEN2KXSI     Define XPG6 XSI things.
   __USE_XOPEN2K8       Define XPG7 things.
   __USE_XOPEN2K8XSI    Define XPG7 XSI things.

which *suggests* that those represent distinct use definitions. but
reading further:

#ifdef  _XOPEN_SOURCE
# define __USE_XOPEN    1
# if (_XOPEN_SOURCE - 0) >= 500
#  define __USE_XOPEN_EXTENDED  1
#  define __USE_UNIX98  1
#  undef _LARGEFILE_SOURCE
#  define _LARGEFILE_SOURCE     1
#  if (_XOPEN_SOURCE - 0) >= 600
#   if (_XOPEN_SOURCE - 0) >= 700
#    define __USE_XOPEN2K8      1
#    define __USE_XOPEN2K8XSI   1
#   endif
#   define __USE_XOPEN2K        1
#   define __USE_XOPEN2KXSI     1

it seems clear that, based on the value of _XOPEN_SOURCE, you get
either both of the related __USE macros, or neither of them. as in,
based on _XOPEN_SOURCE, you'll get both of these defined:

#   define __USE_XOPEN2K        1
#   define __USE_XOPEN2KXSI     1

in other words, using only official feature test macros, you can't,
for example, select XPG6 *without* selecting XPG6 XSI. is that about
right?

  i ask only because if you check the man page for posix_openpt(),
you see the FTM requirement:

  posix_openpt(): _XOPEN_SOURCE >= 600

which covers all of XPG6, but if you look in <stdlib.h>, you see the
more specific XSI-related conditional:

#ifdef __USE_XOPEN2KXSI
/* Return a master pseudo-terminal handle.  */
extern int posix_openpt (int __oflag) __wur;
#endif

  it just seems like there's a bit of fuzziness between what the
developer can specify, and the test being made in the header file.
does that make sense?

  it also makes tests like this in <strings.h> a bit confusing at
first glance:

#if defined __USE_MISC || !defined __USE_XOPEN2K8 || defined __USE_XOPEN2K8XSI

those last two tests seem weird since, if i understand the earlier
stuff correctly, you either get both of those, or neither, so it seems
strange to test whether the first macro is undefined or the *second*
is defined. again, am i making any sense?

  thoughts?

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

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