C 宏 ## 不适用于函数定义

Question

#define FUNCXY(x,y) void FUNC_##x_##y(int){}
#define FUNCXYGOOD(x,y) void FUNCGOOD_##x##_##y(int){}
FUNCXY(2, 1) //get expanded to void FUNC_x_1(int){}
FUNCXYGOOD(2, 1) //get expanded to void FUNCGOOD_2_1(int){}

Why doesn't FUNCXY work but FUNCXYGOOD work, that is the C rule behind this?

Answer 1

The answer is very simple. there is no x_ macro parameter. Underscores are part of the macro token. Underscore is same as any other valid token character

Othersise it would be inposibe to have macro like this:

#define FOO(x, xa, xb)