Re: unique identifiers for guard macros

[Angel Tsankov]

> > > Why do you need unique guards? The reason why header guards are used is
> > > to prevent multiple inclusion of a file so the macros are based on the
> > > file name.
> > >
> > > For example, foo.h would have:
> > >
> > > #ifndef FOO_H
> > > #define FOO_H
> > >
> > > #endif
> > >
> > > Sorry if this isn't very helpful, but I don't see why you would need
> > > unique guards.
> > >
> > > Regards,
> > >
> > > Ryan Mansfield
> >
> > FWIW, I think that MS agrees with you: in VC++, you can write
> > #pragma once
> > at the top of a file instead of guards.
> >
> > I guess that g++ is more hesitant to extend the language (for which MS 
> > is notorious). Since the preprocessor can do the trick (through unique 
> > guards), then that's that. Generating unique names sure is annoying, 
> > though. I try to include into the guard some information that includes 
> > both the file name, and the directory structure relative to the 
> > project's base directory.
>
> Come to think of it, it seems that g++ supports #pragma once as well:
> http://gcc.gnu.org/gcc-3.4/changes.html
>
> That should solve your problem, no?

Hmm, interesting...
I thought g++ did not support #pragma once. I tested it on g++ 3.4.4 and 4.0.0 
and it works!
I think this is a very efficient solution, even more - in my opinion, it should 
be adopted by the standard.