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  1. #include <stdio.h>
  2.  
  3. #define PP_ARG_N(                                        \
  4.      _1,  _2,  _3,  _4,  _5,  _6,  _7,  _8,  _9, _10,    \
  5.     _11, _12, _13, _14, _15, _16, _17, _18, _19, _20,    \
  6.     _21, _22, _23, _24, _25, _26, _27, _28, _29, _30,    \
  7.     _31, _32, _33, _34, _35, _36, _37, _38, _39, _40,    \
  8.     _41, _42, _43, _44, _45, _46, _47, _48, _49, _50,    \
  9.     _51, _52, _53, _54, _55, _56, _57, _58, _59, _60,    \
  10.     _61, _62, _63, N, ...) N
  11.  
  12. #define PP_RSEQ_N()                                      \
  13.     63, 62, 61, 60,                                      \
  14.     59, 58, 57, 56, 55, 54, 53, 52, 51, 50,              \
  15.     49, 48, 47, 46, 45, 44, 43, 42, 41, 40,              \
  16.     39, 38, 37, 36, 35, 34, 33, 32, 31, 30,              \
  17.     29, 28, 27, 26, 25, 24, 23, 22, 21, 20,              \
  18.     19, 18, 17, 16, 15, 14, 13, 12, 11, 10,              \
  19.      9,  8,  7,  6,  5,  4,  3,  2,  1,  0
  20.  
  21. #define PP_COMMASEQ_N()                                  \
  22.     1,  1,  1,  1,                                       \
  23.     1,  1,  1,  1,  1,  1,  1,  1,  1,  1,               \
  24.     1,  1,  1,  1,  1,  1,  1,  1,  1,  1,               \
  25.     1,  1,  1,  1,  1,  1,  1,  1,  1,  1,               \
  26.     1,  1,  1,  1,  1,  1,  1,  1,  1,  1,               \
  27.     1,  1,  1,  1,  1,  1,  1,  1,  1,  1,               \
  28.     1,  1,  1,  1,  1,  1,  1,  1,  0,  0
  29.  
  30. #define PP_COMMA()				,
  31.  
  32. #define PP_HASCOMMA(...)                                 \
  33.     PP_NARG_(__VA_ARGS__, PP_COMMASEQ_N())
  34.  
  35. #define PP_NARG_HELPER1(a, b, N)    	                 \
  36.     PP_NARG_HELPER2(a, b, N)
  37. #define PP_NARG_HELPER2(a, b, N)    			 \
  38.     PP_NARG_HELPER3_ ## a ## b(N)
  39. #define PP_NARG_HELPER3_01(N)			0
  40. #define PP_NARG_HELPER3_00(N)   		1
  41. #define PP_NARG_HELPER3_11(N)   		N
  42.  
  43. #define PP_NARG_(...)    		PP_ARG_N(__VA_ARGS__) 
  44.  
  45. #define PP_NARG(...)					 \
  46.     PP_NARG_HELPER1(					 \
  47.         PP_HASCOMMA(__VA_ARGS__),            		 \
  48.         PP_HASCOMMA(PP_COMMA __VA_ARGS__ ()),        	 \
  49.         PP_NARG_(__VA_ARGS__, PP_RSEQ_N()))
  50.  
  51. #define PP_ISZERO(x)					 \
  52.     PP_HASCOMMA(PP_ISZERO_HELPER_ ## x)
  53. #define PP_ISZERO_HELPER_0    			,
  54.  
  55. #define PP_PREPEND_NARG(...)                             \
  56.     PP_PREPEND_NARG_HELPER1(PP_NARG(__VA_ARGS__), __VA_ARGS__)
  57. #define PP_PREPEND_NARG_HELPER1(N, ...)                  \
  58.     PP_PREPEND_NARG_HELPER2(PP_ISZERO(N), N, __VA_ARGS__)
  59. #define PP_PREPEND_NARG_HELPER2(z, N, ...)               \
  60.     PP_PREPEND_NARG_HELPER3(z, N, __VA_ARGS__)
  61. #define PP_PREPEND_NARG_HELPER3(z, N, ...)               \
  62.     PP_PREPEND_NARG_HELPER4_ ## z (N, __VA_ARGS__)
  63. #define PP_PREPEND_NARG_HELPER4_1(N, ...)	0
  64. #define PP_PREPEND_NARG_HELPER4_0(N, ...)  	N, __VA_ARGS__
  65.  
  66. #define my_func(...)  func(PP_PREPEND_NARG(__VA_ARGS__))
  67.  
  68. int func(int argc, ...)
  69. {
  70.     printf("func() invoked with %d optional arguments\n", argc);
  71.     return argc;
  72. }
  73.  
  74. int main()
  75. {
  76.     my_func(1, 2);
  77.     my_func(1);
  78.     my_func();
  79.     return 0;
  80. }
Success #stdin #stdout 0.01s 2680KB
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Standard input is empty
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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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