variadic macros

[Christof Warlich]

Hi,

is there any way to access individual elements in the body
of a variadic macro? I only found __VA_ARGS__, which always
expands to the complete list.

Thanks for any help,

Christof

 

[Christof Warlich]

It would already help if there would be a way to have something
that expands to the number of arguments being passed to the variadic macro.

 

[Antoninus Twink]

is there any way to access individual elements in the body
of a variadic macro? I only found __VA_ARGS__, which always
expands to the complete list.

Twelve hours, and not a single language lawyer has come along to explain
that you can't. That's because your question is about C99, and the
luddite regulars in this group won't tolerate any discussion of C
standards more recent than the fall of the Berlin Wall.

Anyway, to answer your question, no there's no way in standard C...
there's not even any way using gcc extensions. I don't know about MS or
lcc extensions - maybe you can with them.

To understand why the answer is no, think about how you'd go about
finding out how many arguments were passed to your variadic function...
now ponder doing that in a macro.

The only purpose of variadic macros is to facilitate providing default
arguments for calls to variadic functions, like the usual
fprintf(stderr, __VA_ARGS__) example.

 

[Peter Nilsson]

Not in standard C99.

It would already help if there would be a way to
have something that expands to the number of
arguments being passed to the variadic macro.

There's no shortage on the wish list for standard C.
However that doesn't mean that your actual problem
doesn't have a simple solution.

Perhaps you might like to mention the real problem.
It may be solvable quite easily in standard C.

 

[vippstar]

Not in standard C99. 6.10.3 p 5
The identiï¬er _ _VA_ARGS_ _ shall occur only in the replacement-list
of a function-like macro that uses the ellipsis notation in the parameters..

 

[vippstar]

Whoops; I just realized you meant that accessing individual elements
in the body of a variadic macro is not possible in C99, which is true.
My apologies.