Re: Possible variadic macro bug

[Neil Booth <neil at daikokuya dot demon dot co dot uk>]

Peter Seebach wrote:-

> >They do in 3.0.  But have you read the 2.95.3 manual?  You would see
> >there that, in that version, this use of ## is whitespace-sensitive
> >(daft for what is supposed to be a tokenized preprocessor, I know).
> 
> Oops.  :)  I read about the usage elsewhere, and didn't check the older
> manual (since I was looking at the newer one for comparisons with the
> ISO C stuff).

GCC < 2.96 doesn't understand __VA_ARGS__ anyway.

> >> While I'm at it, the documentation for ISO's __VA_ARGS__ in extend.texi
> >> is misleading.  While it's true that, given
> >> 	#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)
> >> you can't omit the comma, you *could* write
> >> 	#define debug(format ...) fprintf(stderr, format __VA_ARGS__)
> >> in C99, and then the comma is optional.  (See 6.10.3, paragraph 10, for
> >> the description.)
> 
> >Have you tried it?
> 
> I'm just saying it's correct ISO C99.  I haven't tried it, because I don't
> have an ISO C99 compiler.  :)  It would be good for the docs to show how
> to do this using the C99 varargs macro stuff, though; as is, it sounds like
> they're saying you *can't* do that in the ISO C stuff.

It's not correct C99 - C99 requires that arguments be comma separated,
including the "...".  What you wrote above is GCC's named varargs
extension, with what then becomes an illegal use of __VA_ARGS__ on the
right hand side.

Neil.