Variadic macros with zero arguments

Question

I am working on a call macro,

#define CALL(f,...) FN(f)->call((ref(new LinkedList()), __VA_ARGS__)) 

which when called,

CALL(print,2,3,4,5); 

adds 2 3 4 5 to the linked list (, is overloaded to do so) and calls print which expects a linked list which works as expected how ever there are some calls which do not require arguments,

CALL(HeapSize); 

It still takes a linked list but an empty one, above does not work, I am trying to come up with a macro that woud work with either style?

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

Answer 1

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__))) 

Answer 2

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.