pragma GCC diagnostic

[Bruno Haible]

"#pragma GCC diagnostic" has a few limitations, which make it unusable to
resolve warnings like this one:

Jim Meyering wrote in [1]:
>     $ cat in.c
>     int f (void) __attribute__ ((__warn_unused_result__));
>     void g (void) { (void) f (); }
>     $ gcc -Werror -c in.c
>     cc1: warnings being treated as errors
>     in.c: In function 'g':
>     in.c:2: error: ignoring return value of 'f', declared with attribute 
> warn_unused_result

It is a pity that "#pragma GCC diagnostic" [2] cannot be used to get rid of
this warning, for three reasons:

  - gcc's warning is not triggered by a particular option. It's on by
    default. It's not clear what should by the second argument of
    "#pragma GCC diagnostic". An empty string does not work.

  - It would be needed to restore the previous setting after the line.
    But there's no #pragma GCC push-diagnostic/pop-diagnostic.

  - The restriction that the "#pragma GCC diagnostic" should not occur
    inside functions does not lead to maintainable code. We want to have
    the annotation to inhibit the warning to be just one line away from the
    code that triggers the warning.

Bruno

[1] http://lists.gnu.org/archive/html/bug-gnulib/2008-10/msg00278.html
[2] http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html