Variadic macros with zero arguments?

As for the updated question, by the use of auxiliary macro VA_ARGS like the following, the arguments will be expanded as expected.

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EDIT: Digging throug gcc docs I found that adding ## before VA_ARGS removes the , when there are no arguments but with that I can not nest macros, CALL(print,CALL(HeadSize)); this causes CALL not defined error how ever if I separate the the calls it works c++ c preprocessor link|improve this question edited May 5 '11 at 0:29 asked May 5 '11 at 0:01Hamza Yerlikaya10.6k84288 68% accept rate.

1 You can have CALL delegate to different macros depending on the number of arguments it is passed. I demonstrated how to do this in an answer to another question. This does not require any implementation-specific hacks.

– James McNellis May 5 '11 at 0:30 also see stackoverflow.com/questions/5588855/… – Richard Hansen Feb 9 at 3:26.

As for the updated question, by the use of auxiliary macro VA_ARGS like the following, the arguments will be expanded as expected. #define VA_ARGS(...) , ##__VA_ARGS__ #define CALL(f,...) FN(f)->call((ref(new LinkedList()) VA_ARGS(__VA_ARGS__))) Hope this helps.

If you are using GCC, it has an extension to swallow up the comma preceding the __VA_ARGS__. See: gcc.gnu.org/onlinedocs/cpp/Variadic-Macr....

Beat me by 11 seconds :) – mu is too short May 5 '11 at 0:27 Only because yours is more thorough. :) – Scott Moonen May 5 '11 at 0:28 And MSVC, even though not mentioned on their MSDN page, supports the same extension, making everybody's lives a little bit easier. – vanza May 5 '11 at 0:28.

If you're using gcc/g++ there is a way: #define CALL(f,...) FN(f)->call((ref(new LinkedList()), ## __VA_ARGS__)) From the fine manual: ... if the variable arguments are omitted or empty, the `##' operator causes the preprocessor to remove the comma before it. So gcc has an extension/hack specifically for the problem you are facing.

I have edited the question, I have found the same thing in the docs but with it I can not nest macros – Hamza Yerlikaya May 5 '11 at 0:30.

Unfortunately this cannot be done. You will need to define a separate macro to do this call. As you end up with invalid arguments when VA_ARGS is substituted with nothing you end up with a floating , #define CALL0(f) FN(f)->call((ref(new LinkedList()))).

Simply make f part of the ..., and use a separate macro to extract the first argument where you need f.

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