友元声明和友元定义的相互依赖

#include <iostream>
#include<cstdlib>
using namespace std;

class Screen;//前向声明
class Window_Mgr
{
public:
  void reloacate(Screen& s);
};

class Screen
{
  friend void Window_Mgr::reloacate(Screen& s);//必须先定义Window_Mgr,才能将Window_Mgr::relocate设为友元
public:
  Screen(int _x, int _y): x(_x), y(_y){};
  void print()
  {
      cout <<"x: " <<x <<",y: "<<y <<endl;
  }
private:
  int x;
  int y;
};

void Window_Mgr::reloacate(Screen& s)
{
  s.x++;
  s.y++;
}

int main(int argc, char* argv[])
{
  Screen s(0, 0);
  Window_Mgr mgr;
  mgr.reloacate(s);
  s.print();
  system("pause");
  return 0;
}