C99 usage in gcc

[Joe Buck]

On Sat, Jan 31, 2004 at 10:16:59AM -0800, Zack Weinberg wrote:
> Bruce Stephens <bruce@cenderis.demon.co.uk> writes:
> 
> >> It is a pedwarn, hence you need -pedantic also.
> >
> > Which is useful, except that it also complains about:
> >
> > #ifdef __cplusplus
> > // foo
> > #endif
> 
> As it should.  This will be misinterpreted by a plain-C89 compiler;
> comment stripping happens before #ifdef processing.

I disagree.  There should be no warning, because the plain-C89 compiler
will *not* misinterpret this file.  True, the // will not be interpreted
as a comment; since there is no token "//" in C89 it will be interpreted
as two / tokens.  Nevertheless, the token stream with the two / tokens is
ifdef'ed out, so it's a don't care.

Try giving the compiler

#ifdef __cplusplus
/ / foo
#endif

Notice that gcc -pedantic no longer gives a warning.