Re: [Qemu-devel] Re: [PATCH 1/5] HACKING: add preprocessor rules

[Anthony Liguori]

On 08/16/2010 01:05 PM, Blue Swirl wrote:
> On Sun, Aug 15, 2010 at 9:27 PM, Andreas Schwab<address@hidden>  wrote:
>    
> > Blue Swirl<address@hidden>  writes:
> >
> >      
> > > +For variadic macros, stick with C99 syntax:
> > > +
> > > +#define DPRINTF(fmt, ...)                                       \
> > > +    do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
> > >        
> > That's not C99 syntax, the combination with ## is a gcc extension.  In
> > C99 you cannot have an empty __VA_ARGS__.
> >      
> That's too bad, I picked the example from one of our current macros.
> Maybe just s/C99/this/ or perhaps we shouldn't specify any
> non-standard syntax.
>    

We definitely should discourage the GCC syntax [#define fn(arg...)] as 
it's deprecated by the new C99 syntax.  Very specifically, only the '##' 
is an extension and it's a widely adopted one.

Regards,

Anthony Liguori