Friend function: friend class

全局函数做友元  :(1)类中写 friend void func（）{}；
	                       （2）为了好友可以访问我当前的私有属性

整个类做友元类 :（1）类中写 friend  class  Person；
	                        （2）友元类时单向的（A是B的友元类，但B不是A的友元类），不  可传递的（A是C，B是C友元类，A和B不是友元类）
某个成员函数做友元：（1）friend  void   goodGay :: visit()

Case a friend class -----

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

//第一个类
class Buildings
{
	friend class googGay;
public:
	Buildings()
	{
		this->m_BedRoom="卧室";
		this->m_SittingRoom="客厅";
	}
private:
	string m_SittingRoom;
	string m_BedRoom;
};

//第二个类
class googGay
{
public:
	googGay();
	void visit();
private:
	Buildings * building;
};
//类外实现
googGay::googGay()
{
	building = new Buildings;
}
void googGay::visit()
{
	cout<<"朋友正在访问"<<building->m_BedRoom<<endl;
	cout<<"朋友正在访问"<<building->m_SittingRoom<<endl;
}
void test01()
{
	googGay gg;
	gg.visit();
}
int main()
{
	test01();	
	return 0;
}

Case II - friend function

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

class Buildings
{
	friend void test01(); //声明友元函数
public:
	Buildings()
	{
		this->m_BedRoom="卧室";
		this->m_SittingRoom="客厅";
	}
private:
	string m_SittingRoom;
	string m_BedRoom;
};

void test01()
{
	Buildings *p= new Buildings;
	cout<<"朋友正在访问"<<p->m_BedRoom<<endl;
	cout<<"朋友正在访问"<<p->m_SittingRoom<<endl;
}
int main()
{
	test01();
	return 0;
}