Re: is _ISOC95_SOURCE a valid feature test macro or not?

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 03/19/2014 01:30 PM, Robert P. J. Day wrote:
> 
>   another possibly silly observation -- /usr/include/features.h makes
> no mention of _ISOC95_SOURCE in the early comment listing all(?) of
> the possible feature test macros:
> 
>    ... snip ...
>    __STRICT_ANSI__      ISO Standard C.
>    _ISOC99_SOURCE       Extensions to ISO C89 from ISO C99.
>    _ISOC11_SOURCE       Extensions to ISO C99 from ISO C11.
>    _POSIX_SOURCE        IEEE Std 1003.1.
>    ... snip ...
> 
> despite its "USE" macro being mentioned further down in the same
> comment:
> 
>    ... snip ...
>    __USE_ISOC11         Define ISO C11 things.
>    __USE_ISOC99         Define ISO C99 things.
>    __USE_ISOC95         Define ISO C90 AMD1 (C95) things.
>    ... snip ...
> 
> as well as even further down:
> 
> #undef  __USE_ISOC95
> ...
> #ifdef _GNU_SOURCE
> # undef  _ISOC95_SOURCE
> # define _ISOC95_SOURCE 1
> ...
> /* This is to enable the ISO C90 Amendment 1:1995 extension.  */
> #if (defined _ISOC99_SOURCE || defined _ISOC11_SOURCE \
>      || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199409L))
> # define __USE_ISOC95   1
> #endif
> ...
> 
>   i notice in the man pages Changes file the reference that
> _ISOC95_SOURCE is now allegedly bogus:
> 
> feature_test_macros.7
>     Michael Kerrisk  [Joseph S. Myers]
>         Remove mention of bogus _ISOC95_SOURCE macro
>             The _ISOC95_SOURCE macro is defined in <features.h>, but it
>             does nothing. So remove discussion of it, and move some of
>             the discussion of C95 under the ISOC99_SOURCE subhead.

Joseph pointed out to me that defining _ISOC95_SOURCE actually does 
nothing. So it really is bogus. There is the __USE_ISOC95 macro
that is used internally. But, I think for most purposes
we can consider that to be subsumed under C99.

> but there appear to still be a couple checks for it:
> 
> man3/fwide.3:_ISOC95_SOURCE /* Since glibc 2.12 */ ||
> man3/wprintf.3:_ISOC95_SOURCE /* Since glibc 2.12 */ ||

Those to are bogus, and now I've removed them. Thanks for 
catching that.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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