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C: Counting the number of arguments in __VA_ARGS__

+2 votes
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Is there a way to count the number of variadic macro arguments in C?

I found a way to check if the list is empty: examine sizeof(STR((__VA_ARGS__))) where STR is a macro that stringifies its argument. If it is 3, __VA_ARGS__ is empty. I wonder if there is a less hackish approach.

The macro arguments are expressions, but not of a uniform type, so an array-based approach does not work.

posted Dec 12, 2013 by Seema Siddique

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1 Answer

+1 vote
#define PP_NARG( ...) PP_NARG_(__VA_ARGS__,PP_RSEQ_N())
#define PP_NARG_(...) PP_ARG_N(__VA_ARGS__)
#define PP_ARG_N(_1,_2,_3,_4,_5,_6,_7,_8,_9,[..],_61,_62,_63,N,...) N
#define PP_RSEQ_N() 63,62,61,60,[..],9,8,7,6,5,4,3,2,1,0

PP_NARG(A) 1
PP_NARG(A, B) 2
answer Dec 12, 2013 by anonymous
Looks that this returns the 64th argument if the argument list is longer than 63. I don't want to silently produce wrong results if some arbitrary limit is exceeded.
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