#include <stdio.h>
#define PP_ARG_N( \
_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, \
_11, _12, _13, _14, _15, _16, _17, _18, _19, _20, \
_21, _22, _23, _24, _25, _26, _27, _28, _29, _30, \
_31, _32, _33, _34, _35, _36, _37, _38, _39, _40, \
_41, _42, _43, _44, _45, _46, _47, _48, _49, _50, \
_51, _52, _53, _54, _55, _56, _57, _58, _59, _60, \
_61, _62, _63, N, ...) N
#define PP_RSEQ_N() \
63, 62, 61, 60, \
59, 58, 57, 56, 55, 54, 53, 52, 51, 50, \
49, 48, 47, 46, 45, 44, 43, 42, 41, 40, \
39, 38, 37, 36, 35, 34, 33, 32, 31, 30, \
29, 28, 27, 26, 25, 24, 23, 22, 21, 20, \
19, 18, 17, 16, 15, 14, 13, 12, 11, 10, \
9, 8, 7, 6, 5, 4, 3, 2, 1, 0
#define PP_COMMASEQ_N() \
1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 0, 0
#define PP_COMMA() ,
#define PP_HASCOMMA(...) \
PP_NARG_(__VA_ARGS__, PP_COMMASEQ_N())
#define PP_NARG_HELPER1(a, b, N) \
PP_NARG_HELPER2(a, b, N)
#define PP_NARG_HELPER2(a, b, N) \
PP_NARG_HELPER3_ ## a ## b(N)
#define PP_NARG_HELPER3_01(N) 0
#define PP_NARG_HELPER3_00(N) 1
#define PP_NARG_HELPER3_11(N) N
#define PP_NARG_(...) PP_ARG_N(__VA_ARGS__)
#define PP_NARG(...) \
PP_NARG_HELPER1( \
PP_HASCOMMA(__VA_ARGS__), \
PP_HASCOMMA(PP_COMMA __VA_ARGS__ ()), \
PP_NARG_(__VA_ARGS__, PP_RSEQ_N()))
#define PP_ISZERO(x) \
PP_HASCOMMA(PP_ISZERO_HELPER_ ## x)
#define PP_ISZERO_HELPER_0 ,
#define PP_PREPEND_NARG(...) \
PP_PREPEND_NARG_HELPER1(PP_NARG(__VA_ARGS__), __VA_ARGS__)
#define PP_PREPEND_NARG_HELPER1(N, ...) \
PP_PREPEND_NARG_HELPER2(PP_ISZERO(N), N, __VA_ARGS__)
#define PP_PREPEND_NARG_HELPER2(z, N, ...) \
PP_PREPEND_NARG_HELPER3(z, N, __VA_ARGS__)
#define PP_PREPEND_NARG_HELPER3(z, N, ...) \
PP_PREPEND_NARG_HELPER4_ ## z (N, __VA_ARGS__)
#define PP_PREPEND_NARG_HELPER4_1(N, ...) 0
#define PP_PREPEND_NARG_HELPER4_0(N, ...) N, __VA_ARGS__
#define my_func(...) func(PP_PREPEND_NARG(__VA_ARGS__))
int func(int argc, ...)
{
printf("func() invoked with %d optional arguments\n", argc);
return argc;
}
int main()
{
my_func(1, 2);
my_func(1);
my_func();
return 0;
}
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