Re: [PATCH] Handle gcc -std=c99 -D_XOPEN_SOURCE=600 [BZ #284]

[Roland McGrath <roland at redhat dot com>]

> On Fri, Jul 23, 2004 at 01:19:46PM -0700, Ulrich Drepper wrote:
> > Joseph S. Myers wrote:
> > 
> > > c99 is the name of the compiler to "accept source code conforming to the
> > > ISO C standard".  For example,
> > 
> > And once -D_POSIX_C_SOURCE=200112L is defined all this ISO C nonsense
> > must be completely out of the way.  No __STRICT_ANSI__, since non-ISO C
> > stuff is used.  The same applies to a few other defines.  Only if none
> > is defined can this silly strict ISO C business take place.
> 
> I guess it all depends what exact meaning __STRICT_ANSI__ is supposed to have.
> Either its definition chooses only ISO C90 (resp. C99) features in the
> headers, or it can be combined with other feature set macros with the result
> of a union between ISO C90 (resp. C99) features and features selected by
> the other feature macros.
> The __STRICT_ANSI__ documentation in info gcc doesn't seem to favor either
> of these definitions, at least in my reading.

I think this bit here:

     The `-ansi' option does not cause non-ISO programs to be rejected
     gratuitously.  For that, `-pedantic' is required in addition to
     `-ansi'.  *Note Warning Options::.

leans in the direction of allow combination of -ansi with feature macros.
However, I think it is also reasonable to say that -ansi is a bit archaic.
The important useful case is when someone wants to compile their program
and ensure it is strictly conformant to POSIX, i.e. using non-ISO-C
interfaces specified by POSIX, but not using C language extensions.  As I
understand it, this is supported just fine with -std=c99
-D_POSIX_C_SOURCE=something.  So I don't off hand see the need for people
to use -ansi.