宏可变参数量

网上有很多示例代码，但是总有各种各样的问题，这里总结一下个人测试可用的代码（vs2019）

#define VA_ARGS_PASS(...) ( __VA_ARGS__ )

#define VA_ARGS_COUNT(...) VA_ARGS_COUNT_ VA_ARGS_PASS(__VA_ARGS__, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
#define VA_ARGS_COUNT_(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10, _a11, _a12, _a13, _a14, _a15, _a16, _last, ...) _last

gcc可用方式如下（原文链接）

#define FL_ARG_COUNT(...) FL_INTERNAL_ARG_COUNT_PRIVATE(0, ##__VA_ARGS__,\
    64, 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 FL_INTERNAL_ARG_COUNT_PRIVATE(\
     _0,  _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, _64, N, ...) N
    
// 测试代码 
FL_ARG_COUNT()                  ->0
FL_ARG_COUNT(1)                 ->1
FL_ARG_COUNT(1,2)               ->2
FL_ARG_COUNT(1,2,3)             ->3
FL_ARG_COUNT(1,2,3,4)           ->4
FL_ARG_COUNT(1,2,3,4,5)         ->5
FL_ARG_COUNT(1,2,3,4,5,6)       ->6
FL_ARG_COUNT(1,2,3,4,5,6,7)     ->7
FL_ARG_COUNT(1,2,3,4,5,6,7,8)   ->8
FL_ARG_COUNT(1,2,3,4,5,6,7,8,9) ->9
FL_ARG_COUNT(1,2,3,4,5,6,7,8,9,10)  ->10
FL_ARG_COUNT(\
        1,2,3,4,5,6,7,8,9,10,\
        1,2,3,4,5,6,7,8,9,10,\
        1,2,3,4,5,6,7,8,9,10,\
        1,2,3,4,5,6,7,8,9,10,\
        1,2,3,4,5,6,7,8,9,10,\
        1,2,3,4,5,6,7,8,9,10,\
        1,2,3,4\
        )                      ->64