使用指向成员和宏的指针

Question

I'm having problems with the following code:

#include<iostream>
#include<utility>

#define Row *prow
#define Col *pcol

typedef unsigned int uint;
typedef std::pair<uint, uint> Node;

uint Node::Row = &Node::first;
uint Node::Col = &Node::second;

int main()
{
    Node node(1,2);
    std::cout << node.*prow << node.*pcol << '\n';    // OK
    std::cout << node.Row << node.Col << '\n';        // doesn't compile
}

The idea was to use std::pair but replace first and second with other names, in that case Row and Col . However, the last line doesn't compile even though it should be exactly the same as the line before it. I'd really appreciate if someone could explain me why it happens. I'm using VS2015.

Edit: compiler error C2059 syntax error:'*'

Answer 1

.* is a single token. Your macro is generating two adjacent tokens, . and * , which is not the same thing. (Or at least it might do. Almost certainly you're invoking undefined behaviour.)

There's probably a solution involving token pasting, but you'd do yourself a big favour (and make Bjarne happy) by just not using macros in C++.