On 03/19/2014 03:48 AM, Mike Frysinger wrote: > On Tue 18 Mar 2014 15:46:43 Robert P. J. Day wrote: >> just noticed under /usr/include on my fedora rawhide system the >> following: >> >> /usr/include/bits/environments.h:# define __ILP32_OFFBIG_CFLAGS "-m32 >> -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64" >> /usr/include/python3.3m/pyconfig-64.h:#define _LARGEFILE_SOURCE 1 >> /usr/include/features.h: _LARGEFILE_SOURCE Some more functions for > correct >> standard I/O. /usr/include/features.h:# undef _LARGEFILE_SOURCE >> /usr/include/features.h:# define _LARGEFILE_SOURCE 1 >> /usr/include/features.h:#ifdef _LARGEFILE_SOURCE >> /usr/include/python2.7/pyconfig-64.h:#define _LARGEFILE_SOURCE 1 >> >> but there's no mention of "_LARGEFILE_SOURCE" in "man >> feature_test_macros". is that assumed to be implied by >> _LARGEFILE64_SOURCE? it's not clear. > > nope, none of the three LFS flags imply each other, nor should they. they're > related, but orthogonal by design. > > i could have sworn i saw a description of them in POSIX, but i can't find it > now. the GNU C library manual covers it though: > https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html > > here's a terse summary off the top of my head: > > _LARGEFILE_SOURCE: expose prototypes for new funcs which POSIX got wrong > originally. e.g. fseek & ftell utilize "long", so fseeko & ftello were added > which use "off_t". Thanks, Mike. I'd forgotten those details. So, as far as I can see, _LARGEFILE_SOURCE is largely of (ancient) historical interest, so I don't think I'll bother adding it to the FTM(7) page. Cheers, Michael > _LARGEFILE64_SOURCE: expose prototypes for 64-bit variant funcs w/out > affecting any existing funcs. e.g. you now have fseeko64 & ftello64 which > take explicit off64_t types while fseeko and ftello are unchanged. makes > sense when sizeof(off_t) == 4 && sizeof(off64_t) == 8. > > _FILE_OFFSET_BITS: explicitly set the off_t size. set it to 32 if you want > sizeof(off_t) == 4, or set it to 64 if you want sizeof(off_t) == 8. > > in the ideal world, _FILE_OFFSET_BITS should default to 64 and > _LARGEFILE_SOURCE should default to defined. in our crap world, apps should > be always building with these in their CPPFLAGS. > -mike > -- 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
