Re: should "man feature_test_macros" mention _LARGEFILE_SOURCE?

[Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>]

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On Wed 19 Mar 2014 14:37:51 Michael Kerrisk wrote:
> 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.htm
> > l
> > 
> > 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.

would be nice to document it ... i tend to get more confused when something is 
left out entirely even if it was done on purpose.  especially since it'd give 
us the opportunity to discourage people from using it and drive people towards 
the One True Way when it comes to LFS flags.
-mike

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