相关疑难解决方法(0)

我有两个宏,FOO2并且FOO3:

#define FOO2(x,y) ...
#define FOO3(x,y,z) ...

我想定义一个新的宏FOO如下:

#define FOO(x,y) FOO2(x,y)
#define FOO(x,y,z) FOO3(x,y,z)

但这不起作用,因为宏不会在参数数量上超载.

无需修改FOO2和FOO3,是有一些方法来定义一个宏FOO(使用__VA_ARGS__或以其他方式),以获得分派的相同的效果FOO(x,y)来FOO2,并FOO(x,y,z)到FOO3？

我正在根据递归宏和 C++20 的伟大手册构建代码__VA_OPT__： https://www.scs.stanford.edu/~dm/blog/va-opt.html

代码是

#include <iostream>

#define PARENS ()

// Rescan macro tokens 256 times
#define EXPAND(arg) EXPAND1(EXPAND1(EXPAND1(EXPAND1(arg))))
#define EXPAND1(arg) EXPAND2(EXPAND2(EXPAND2(EXPAND2(arg))))
#define EXPAND2(arg) EXPAND3(EXPAND3(EXPAND3(EXPAND3(arg))))
#define EXPAND3(arg) EXPAND4(EXPAND4(EXPAND4(EXPAND4(arg))))
#define EXPAND4(arg) arg

#define FOR_EACH(macro, ...)                                    \
  __VA_OPT__(EXPAND(FOR_EACH_HELPER(macro, __VA_ARGS__)))
#define FOR_EACH_HELPER(macro, a1, ...)                         \
  macro(a1)                                                     \
  __VA_OPT__(FOR_EACH_AGAIN PARENS (macro, __VA_ARGS__))
#define FOR_EACH_AGAIN() FOR_EACH_HELPER

#define ENUM_CASE(name) case name: return #name;

#define MAKE_ENUM(type, ...)                    \
enum type {                                     \
  __VA_ARGS__                                   \
};                                              \
constexpr const char *                          \
to_cstring(type _e)                             \
{ …