20240417，友元 FRIEND

··················本来要学习的吃瓜吃了一下午

目录

3.1 全局函数做友元

3.2 友元类

3.3 成员函数做友元

三，友元

3.1 全局函数做友元

#include<iostream>
using namespace std;
class Building
{
	friend void goodGay(Building* building);
	//好朋友，可以访问buiding的全部成员
public:
	Building()
	{
		m_SittingRoom = "客厅";
		m_BedRoom = "卧室";
	}
	string m_SittingRoom;
private:
	string m_BedRoom;
};
void goodGay(Building *building)
{
	cout << "好基友的全局函数  正在访问：" << building->m_SittingRoom << endl;
	cout << "好基友的全局函数  正在访问：" << building->m_BedRoom << endl;
}
void test01()
{
	Building bding;
	goodGay(&bding);
}
int main()
{
	test01();
	system("pause");
	return 0;
}

3.2 友元类

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

class Goodgay
{
public:
	Goodgay();
	void visit();//参观函数，访问BUIDING中的属性
	Building * building;
};

class Building
{
	friend Goodgay;//GoodGAY类是BUILDING类的好朋友，可以访问BUILDING的私有成员
public:
	Building();
	string m_SittingRoom;
private:
	string m_BedRoom;
};

Building::Building()//类外写成员函数
{
	m_SittingRoom = "客厅";
	m_BedRoom = "卧室";
}
Goodgay::Goodgay()
{
	//创建一个建筑物的对象
	building = new Building;//堆区创建一个BUILDING的对象
	//构造函数解决初始化问题，所以？这是初始化？*building指向这个堆区对象
}
void Goodgay::visit()
{
	cout << "好基友类正在访问：" << building->m_SittingRoom << endl;
	cout << "好基友类正在访问：" << building->m_BedRoom << endl;
}
void test01()
{
	Goodgay gg;
	gg.visit();
}
int main()
{
	test01();
	system("pause");
	return 0;
}

3.3 成员函数做友元

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

class Goodgay
{
public:
	Goodgay();
	void visit();//可以访问Buiding私有
	void visit01();//不可以访问Buiding私有
	Building * building;
};

class Building
{
	//friend void visit();这种写法会将VISIT识别为一个全局函数，而不是Goodgay中的成员函数
	friend void Goodgay::visit();
public:
	Building();
	string m_SittingRoom;
private:
	string m_BedRoom;
};

Building::Building()//类外写成员函数
{
	m_SittingRoom = "客厅";
	m_BedRoom = "卧室";
}
Goodgay::Goodgay()
{
	//创建一个建筑物的对象
	building = new Building;//堆区创建一个BUILDING的对象，返回指针
	//构造函数解决初始化问题，所以？这是初始化？building指向这个堆区对象
}
void Goodgay::visit()
{
	cout << "好基友类visit 正在访问：" << building->m_SittingRoom << endl;
	cout << "好基友类visit 正在访问：" << building->m_BedRoom << endl;
}
void Goodgay::visit01()
{
	cout << "好基友类visit01  正在访问：" << building->m_SittingRoom << endl;
	//cout << "好基友类visit01 正在访问：" << building->m_BedRoom << endl;
}
void test01()
{
	Goodgay gg;
	gg.visit();
	gg.visit01();
}
int main()
{
	test01();
	system("pause");
	return 0;
}

想让谁访问，就让谁FRIEND