c++ 引用类型以及函数指针

#include "stdafx.h"
#include <iostream>
#include <string>
#include <fstream>
#include <cmath>
using namespace std;
typedef int& ex(int &, int &);
int& exchange(int &, int &);
void acb(ex,int &,int &);

int main() {
    int a = 123,b = 999;
    acb(exchange, a, b);
    cout << a << "   " << b << endl;
    system("pause");
}

void acb(ex e,int &a,int &b) {
    cout << e << endl;
    ex *exx = e;
    exx(a, b) = 998;
    //cout << exx(a, b) << endl;
}

int& exchange(int &a, int &b) {
    int temp;
    temp = a;
    a = b;
    b = temp;
    double c = 1.3;
    return b;
}