C++中级-friend关键字访问类中private

全局函数做友元

#if 0
#include <iostream>
#include <string>
using namespace std;

//用friend关键字访问类中private的函数方法。

class Building {

    //2.在此用friend关键字声明!
    friend void SeePrivate(Building* b);

public:
    Building() {
        Mainroom = "客厅";
        Bedroom = "卧室";
    }

public:
    string Mainroom;

private:
    string Bedroom;

};

//1.通过全局函数做友元访问Private数据
void SeePrivate(Building* b) {
    cout << b->Bedroom << endl;
};



int main() {
    Building b;
    //3.只能访问public中的Mainroom。不能访问private中的Bedroom。
    cout << b.Mainroom << endl;
    //cout << b.Bedroom << endl;

    SeePrivate(&b);
    return 0;
}
#endif // 0

类做友元

#if 0
#include <iostream>
#include <string>
using namespace std;

//用friend关键字访问类中private的函数方法。

class Building {

    //2.在此用friend关键字声明!
    friend void SeePrivate(Building* b);

public:
    Building() {
        Mainroom = "客厅";
        Bedroom = "卧室";
    }

public:
    string Mainroom;

private:
    string Bedroom;

};

//1.通过全局函数做友元访问Private数据
void SeePrivate(Building* b) {
    cout << b->Bedroom << endl;
};



int main() {
    Building b;
    //3.只能访问public中的Mainroom。不能访问private中的Bedroom。
    cout << b.Mainroom << endl;
    //cout << b.Bedroom << endl;

    SeePrivate(&b);
    return 0;
}
#endif // 0

成员函数做友元

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



class Building {
　　//3.声明此函数；
    friend void Friends::SeeBuilding();
public:
    Building()
    {
    Mainroom = "客厅";
    Bedroom = "卧室";
    };

public:
    string Mainroom;

private:
    string Bedroom;

};


class Friends {
public:
    
    //1.创建一个要访问的类的指针对象
    Building* bud;

    //2.在堆区创建一个Building对象
    Friends(){bud = new Building;};

    void SeeBuilding(){
    cout << bud->Mainroom << endl;
    //4.虽然编译器报错，但是能访问Building类中的pravite数据了、
    cout << bud->Bedroom << endl;
    };

    

};


int main() {
    Friends f;
    f.SeeBuilding();
    return 0;
}