C++学习 --- 类和对象之友元

四、友元

1、全局函数做友元

#include <iostream>
#include <string>
using namespace std;
​
//建筑物
class Building {
​
//告诉编译器，GoodGay 全局函数是Building的好朋友，可以访问Building中的私有成员
friend void GoodGay(Building * building);
​
public:
    Building() {
        m_SittingRoom = "客厅";
        m_BedRoom = "卧室";
    }
public:
    string m_SittingRoom; //客厅
private:
    string m_BedRoom;     //卧室
};
​
//全局函数
void GoodGay(Building * building) {
    cout << "好基友全局函数正在访问: " << building->m_SittingRoom << endl;
    cout << "好基友全局函数正在访问: " << building->m_BedRoom << endl;
}
​
void test01() {
    Building building;
    GoodGay(&building);
}
​
int main() {
    test01();
    
    system("pause");
    return 0;
}

 

2、类做友元

#include <iostream>
#include <string>
using namespace std;
​
class Building;
​
//类做友元
class GoodGay {
public:
    GoodGay();
    ~GoodGay();
​
public:
    void visit();//参观函数，访问Building中的属性
    Building * building;
};
​
class Building {
    //GoodGay是本类的好朋友，可以访问本类中的私有
    friend class GoodGay;
​
public:
    Building();
​
public:
    string m_SittingRoom;   //客厅
private:
    string m_BedRoom;       //卧室
};
​
//类外实现成员函数
Building::Building() {
    m_SittingRoom = "客厅";
    m_BedRoom = "卧室";
}
​
GoodGay::GoodGay() {
    //创建建筑物对象
    building = new Building;
}
GoodGay::~GoodGay() {
    delete building;
}
​
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、成员函数做友元

#include <iostream>
#include <string>
using namespace std;
​
//成员函数做友元
​
class Building;
class GoodGay {
public:
    GoodGay();
    ~GoodGay();
    
    void visit();   //让visit 函数  可以访问Building中的私有成员
    void visit2();  //让visit2函数不可以访问Building中的私有成员
    
    Building * building;
};
​
class Building {
    //告诉编译器 GoodGay 类下的visit成员函数作为本类的好友，可以访问私有成员
    friend void GoodGay::visit();
public:
    Building();
​
public:
    string m_SittingRoom; //客厅
private:
    string m_BedRoom;     //卧室
};
​
//类外实现成员函数
GoodGay::GoodGay() {
    building = new Building;
}
​
GoodGay::~GoodGay() {
    delete building;
}
​
void GoodGay::visit() {
    cout << "visit 函数正在访问: " << building->m_SittingRoom << endl;
    cout << "visit 函数正在访问: " << building->m_BedRoom << endl;
}
void GoodGay::visit2() {
    cout << "visit2 函数正在访问: " << building->m_SittingRoom << endl;
    //cout << "visit2 函数正在访问: " << building->m_BedRoom << endl;
​
}
​
Building::Building() {
    m_SittingRoom = "客厅";
    m_BedRoom = "卧室";
}
​
void test01() {
    GoodGay gg;
    gg.visit();
    gg.visit2();
}
​
int main() {
    test01();
    
    system("pause");
    return 0;
}