类与对象_友元

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

//建筑物类 
class Building {
    //该全集函数是Building类的友元函数 可以访问私有成员 
    friend GoodFriend(Building &building);
    public:
        Building() {
            m_SittingRoom = "客厅";
            m_BedRoom = "卧室";
        }
        
        string m_SittingRoom; //客厅
        
    private:
         string m_BedRoom;//卧室 
        
};

//全局函数
GoodFriend(Building &building) {
    cout << "全局函数正在访问" << building.m_SittingRoom << endl;
    cout << "全局函数正在访问" << building.m_BedRoom << endl;
    
}

int main() { 
    Building building;
    GoodFriend(building);
}

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

//建筑物类 
class Building {
    public:
        friend class GoodFriend;//友元类 
        Building();
        string m_SittingRoom; //客厅
        
    private:
         string m_BedRoom;//卧室 
        
};

//友元类
class GoodFriend {
    public:
        GoodFriend();
        void visit(); //参观函数 访问Building中的属性
        Building * building; 
};

//类外写成员函数 
Building::Building() {
    m_SittingRoom = "客厅";
    m_BedRoom = "卧室";
} 

GoodFriend::GoodFriend() {
    //创建建筑物对象
    building = new Building;
}

void GoodFriend::visit() {
    cout << "友元类正在访问" << building->m_SittingRoom << endl;
    cout << "友元类正在访问" << building->m_BedRoom << endl;
}


int main() { 
    GoodFriend gf;
    gf.visit();
}

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

class Building;

class GoodFriend {
    public:
        GoodFriend();
        
        void visit(); //visit可以访问Building中的私有成员 
        void visit2(); //visit2不可以访问Building中的私有成员 
        
        Building * building; 
};

//建筑物类 
class Building {
    public:
        friend void GoodFriend::visit();//成员函数做友元
        
        Building();
        
        string m_SittingRoom; //客厅
        
    private:
         string m_BedRoom;//卧室 
        
};


//类外写成员函数 
Building::Building() {
    m_SittingRoom = "客厅";
    m_BedRoom = "卧室";
} 

GoodFriend::GoodFriend() {
    //创建建筑物对象
    building = new Building;
}

void GoodFriend::visit() {
    cout << "成员函数正在访问" << building->m_SittingRoom << endl;
    cout << "成员函数正在访问" << building->m_BedRoom << endl;
}

void GoodFriend::visit2() {
    cout << "成员函数正在访问" << building->m_SittingRoom << endl;
    //cout << "友元类正在访问" << building->m_BedRoom << endl;      // 无法访问 
}


int main() { 
    GoodFriend gf;
    gf.visit();
}