C++基础-友元函数(friend class)

当基类中的函数被protected的时候，只有继承的子类才能访问，为了使得非继承的类也可以使用，使用friend class (类名)来进行操作

#include <iostream>

using namespace std;

class Lover{
public:
    Lover(string theName);
    void kiss(Lover *lover);
    void ask(Lover *lover, string something);

protected:
    string name;
    friend class Others; //构造友元函数, 使得Others可以调用name属性 
};
Lover::Lover(string theName) {
    name = theName;
}

void Lover::kiss(Lover *lover) {
    cout << name << "kiss" << lover->name << endl;
}

void Lover::ask(Lover *lover, string something){
    cout << name << "ask" << lover->name << "do" << something << endl;
}

class Boyfriend:public Lover {
public:
    Boyfriend(string theName);
};

Boyfriend::Boyfriend(string theName) : Lover(theName){ //进行有参数的继承

}
class Girlfriend:public Lover {
public:
    Girlfriend(string theName);
};

Girlfriend::Girlfriend(string theName) : Lover(theName){}

class Others {
public:
    Others(string theName);
    void kiss(Lover *lover);
protected:
    string name;
};

Others::Others(string theName) {
    name = theName;
}
void Others::kiss(Lover *lover) {
    cout << name << "亲一下" << lover->name << endl; //因为name是protected, 如果没有友元就不能进行访问 
}


int main() {

    Boyfriend boyfriend("A君");
    Girlfriend girlfriend("B妞");

    Others others("路人甲");

    girlfriend.kiss(&boyfriend);
    girlfriend.ask(&boyfriend, "洗衣服啦");

    cout << "\n当当当:传说的路人甲登场...\n";
    others.kiss(&girlfriend);
}