Re: glthread_cond_timedwait errors on C99 code

[Tim Rühsen]

On Samstag, 30. September 2017 16:31:22 CEST Bruno Haible wrote:
> Tim Rühsen wrote:
> > The line
> > 
> >     return glthread_cond_timedwait(&cond->cond, &mutex->mutex, &(struct
> > 
> > timespec){ .tv_sec = ms / 1000, .tv_nsec = (ms % 1000) * 1000000 });
> > 
> > errors with
> > 
> > thread.c:155:136: error: macro "glthread_cond_timedwait" passed 4
> > arguments, but takes just 3
> > 
> >   return glthread_cond_timedwait(&cond->cond, &mutex->mutex, &(struct
> > 
> > timespec){ .tv_sec = ms / 1000, .tv_nsec = (ms % 1000) * 1000000 });
> 
> That's because glthread_cond_timedwait is a macro, and you are passing it
> the arguments
>         &cond->cond
>         &mutex->mutex
>         &(struct timespec){ .tv_sec = ms / 1000
>         .tv_nsec = (ms % 1000) * 1000000 }
> 
> > This is with gcc 7.2.0 in C99 (default) mode. Is it the preprocessor, my
> > code or the macro broken ? Or a general C99 flaw ?
> > BTW, putting brackets () around the last argument makes it compile.
> 
> It's a general C flaw: The C preprocessor considers only opening
> parentheses, closing parentheses, and commas as syntactically relevant.
> Everything else are "other tokens". A consequence of this is that you need
> to use extra parentheses when passing comma-expressions or struct
> initializers to macros.

Thanks for your explanation, Bruno :-)

Regards, Tim

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