#include <iostream>
using namespace std;
class Second;  //前向引用聲明
class First
{	Second *x;
public:
	void callSecond()
   {x->funFirst();}    //錯誤：在Second類定義之前使用了該類的函數(shù)
};
class Second
{	First *y;
public:
	void funFirst()		
   {cout<<"This is calling Second"<<endl;}
};
int main()		
{	First a;	a.callSecond();	return 0;}