Counting the number of arguments in __VA_ARGS__

[Florian Weimer]

On 12/12/2013 02:21 PM, vijay nag wrote:
> On Thu, Dec 12, 2013 at 6:38 PM, Florian Weimer <fweimer@redhat.com> wrote:
>> 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.
>>
>> --
>> Florian Weimer / Red Hat Product Security Team
>
> #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

Hmm.  I think 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.

-- 
Florian Weimer / Red Hat Product Security Team