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#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;
}
Success #stdin #stdout 0.01s 2680KB
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stdin
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Standard input is empty
stdout
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func() invoked with 2 optional arguments
func() invoked with 1 optional arguments
func() invoked with 0 optional arguments
https://ideone.com/m15OG
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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