调用没有括号的类似函数的宏吗？

Question

Suppose that we pass the following to the gcc 's preprocessor:

#define REM(...) __VA_ARGS__
#define PAIR(x) REM x

PAIR((a)b)

It expands PAIR((a)b) into ab . How does this happen? I am confused about REM being used without parentheses and x not being echoed as is...

Answer 1

When you write:

PAIR((a)b)

given the definition

PAIR(x) REM x

that means x = (a)b . So, we can write out the right hand side as

REM (a)b

right?

Now REM(a) is just a , so REM (a)b is just ab (tokens are separated by whitespace unless you explicitly use token pasting).