32. 友元

• 友元

• 全局函数作为友元函数

• 利用friend关键字让全局函数 goodGay作为本类好朋友，可以访问私有成员
• friend void goodGay(Building * buliding);

• 类作为友元类

• 让goodGay类作为 Building的好朋友，可以访问私有成员
• friend class GoodGay;

• 类中的成员函数作为友元函数

• //让GoodGay类中的 visit成员函数作为友元
• friend void GoodGay::visit();

例如卧室是私有的，通常只能自己访问，但对于闺蜜，可能可以单独让他访问，这个闺蜜就是类似友元。

全局函数作为友元函数

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

class Building
{
	//利用friend关键字让全局函数  goodGay作为本类好朋友，可以访问私有成员
	friend void goodGay(Building * buliding);

public:
	Building()
	{
		this->m_SittingRoom = "客厅";
		this->m_BedRoom = "卧室";
	}

public:
	string m_SittingRoom; //客厅
private:
	string m_BedRoom; //卧室
};

//好基友全局函数  可以访问Building的私有属性
void goodGay( Building * buliding)
{
	cout << "好基友正在访问：" << buliding->m_SittingRoom << endl;

	cout << "好基友正在访问：" << buliding->m_BedRoom << endl;
}

void test01()
{
	Building buliding;
	goodGay(&buliding);
}

int main(){
	test01();
	

	system("pause");
	return EXIT_SUCCESS;
}

类作为友元类

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include <string>
class Building;
class GoodGay
{
public:

	GoodGay();

	void visit();

	Building * m_building;
};

class Building
{
	//让goodGay类作为 Building的好朋友，可以访问私有成员
	friend class GoodGay;

public:
	Building();

	string m_SittingRoom;

private:
	string m_BedRoom;
};

Building::Building()
{
	this->m_SittingRoom = "客厅";
	this->m_BedRoom = "卧室";
}

GoodGay::GoodGay()
{
	this->m_building =  new Building;
}

void GoodGay::visit()
{
	cout << "好基友正在访问： " << this->m_building->m_SittingRoom << endl;
	cout << "好基友正在访问： " << this->m_building->m_BedRoom << endl;
}

void test01()
{
	GoodGay gg;
	gg.visit();
}

int main(){

	test01();

	system("pause");
	return EXIT_SUCCESS;
}

类中的成员函数作为友元函数

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include <string>
class Building;
class GoodGay
{
public:

	GoodGay();

	void visit(); //可以访问building的私有

	void visit2(); // 不可以访问building的私有

	Building * m_building;
};

class Building
{
	//让GoodGay类中的 visit成员函数作为友元
   friend void GoodGay::visit();
public:
	Building();

	string m_SittingRoom;

private:
	string m_BedRoom;
};

Building::Building()
{
	this->m_SittingRoom = "客厅";
	this->m_BedRoom = "卧室";
}

GoodGay::GoodGay()
{
	this->m_building = new Building;
}

void GoodGay::visit()
{
	cout << "好基友正在访问： " << this->m_building->m_SittingRoom << endl;
	cout << "好基友正在访问： " << this->m_building->m_BedRoom << endl;
}

void GoodGay::visit2()
{
	cout << "好基友正在访问： " << this->m_building->m_SittingRoom << endl;
	//cout << "好基友正在访问： " << this->m_building->m_BedRoom << endl;
}


void test01()
{
	GoodGay gg;
	gg.visit();
	gg.visit2();
}

int main(){

	test01();

	system("pause");
	return EXIT_SUCCESS;
}