On Wed, Mar 19, 2014 at 2:48 PM, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote: > > 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. Yes, they are. Translate the above parlance as follows XPG == POSIX Base specification XSI == POSIX base specification + XSI extension (Since I know you have it, see also TLPI pages 14, 15, and 61ff) > 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 But note that there is also: #if (_POSIX_C_SOURCE - 0) >= 200112L # define __USE_XOPEN2K 1 ... #endif So, __USE_XOPEN2K might be set when __USE_XOPEN2KXSI is not. > in other words, using only official feature test macros, you can't, > for example, select XPG6 *without* selecting XPG6 XSI. is that about > right? See above. > 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 See my comments above. Cheers, Michael > 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 > ======================================================================== > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
