C++ 友元函数 友元类

#include <stdio.h>#include <iostream>using namespacestd;//友元函数class Girl{public:    friendvoid changeAge(Girl *girl,int age);//友元函数    friendclass Boy;//友元类    int tell();private:    int age;};int Girl::tell(){    cout<<"age:"<<age<<endl;    return0;}void changeAge(Girl *girl,int age){    girl->age = age;}//友元类class Boy{public:    Boy(Girl girl){        this->girl = girl;    }    void introduce(){        cout<<"介绍girl年龄： "<<girl.age<<endl;    }    void changeGirl(){        girl.age =28;    }private:    Girl girl;};int main(){    /*      Girl * girl = new Girl();    girl->tell();    changeAge(girl, 16);    girl->tell();    delete girl;    return 0;*/    Girl girl;    Boy boy =Boy(girl);    boy.introduce();    boy.changeGirl();    boy.introduce();    return0;}