生活中你的家有客厅(Public),有你的卧室(Private)
客厅所有来的客人都可以进去，但是你的卧室是私有的，也就是说只有你能进去
但是呢，你也可以允许你的好闺蜜好基友进去。
在程序里，有些私有属性也想让类外特殊的一些函数或者类进行访问， 就需要用到友元的技术
友元的目的就是让一个函数或者类访问另-个类中私有成员
友元的关键字为friend I
友元的三种实现
●全局函数做友元
●类做友元
●成员函数做友元
我们先用第一种实现友元函数全局函数做友元：
#include<iostream>
#include<string>
using namespace std;class Building{//告诉编译器goodGay全局函数是Building类的好朋友，可以访问类中的私有内容friend void goodGay(Building * building);
public:Building() {this->m_SittingRoom = "客厅";this->m_BedRoom = "卧室";}
public:string m_SittingRoom; //客厅
private:string m_BedRoom; //卧室
};
void goodGay(Building * building) {cout << "好基友正在访问:" << building->m_SittingRoom << endl;cout << "好基友正在访问: "<< building->m_BedRoom << endl;
}void test01(){Building b;goodGay(&b);
}
int main() {test01();system("pause");
}类做友元：
#include<iostream>
#include<string>
using namespace std;class Building;
class goodGay{public:goodGay();void visit();private:Building * building;
};
class Building{//告诉编译器goodGay类是Building美的好朋友，可以访问到Building类中私有内容friend class goodGay;public:Building();public:string m_SittingRoom; //客厅private:string m_BedRoom;//卧室};Building::Building() {this->m_SittingRoom = "客厅";this->m_BedRoom = "卧室";
}
goodGay::goodGay() {building = new Building;}
void goodGay :: visit(){cout << "好基友正在访问"<< building->m_SittingRoom << endl;cout << "好基友正在访问"<< building->m_BedRoom << endl;
}void test01() {goodGay gg;gg.visit();
}int main() {test01();system("pause");
}成员函数做友元：
#include<iostream>
#include<string>
using namespace std;class Building {//告诉编译器goodGay全 局函数是Building类的好朋友，可以访问类中的私有内容friend void goodGay(Building * building);public:Building(){this->m_SittingRoom = "客厅";this->m_BedRoom = "卧室";}public:string m_SittingRoom; //客厅private:string m_BedRoom; //卧室};void goodGay(Building * building) {cout << "好基友正在访问:" << building-> m_SittingRoom << endl;cout << "好基友正在访问:" << building->m_BedRoom << endl;
}void test01() {Building b;goodGay(&b);
}
int main() {test01();system("pause");return 0;
}
)
)
