定义一个Girl类和一个Boy类，这两个类中都有表示姓名、年龄的私有数据成员，都要定义构造西数、析构西数、输出成员变量信息的公有成员函数。 1）在Girl 类中定义成员函数 VisitBoy (Boy&)，并声明为Boy 类的友元成员，从而访问 Boy 类的私有成员。 （2）删除 Girl 类的成员函数 VisitBoy (Boy &），定义一个普通西数 visitBoyGirl (Boy&,Girl &)，作为以上两个类的友元，通过调用该函数输出 Boy 和Girl 的信息。 定义友元类的主西数可参考如下： int main ( { Girl girl ("ZHOU Yuxing", 16) ; Boy boy ("Chen Qi", 15); girl. Print (); boy. Print (); girl. VisitBoy (boy); return 0; ] 定义友元函数的主西数可参考如下： int main () { Girl girl ("ZHOU Yuxing", 16) : Boy boy ("Chen Qi", 15); girl. Print; boy. Print 0 ; VisitBoyGirl (boy, girl); return 0;

Girl类的定义如下：

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

class Boy; //前置声明Boy类

class Girl {
private:
    string name;
    int age;
public:
    Girl(string n, int a) : name(n), age(a) {}
    ~Girl() {}

    void Print() {
        cout << "Girl's name: " << name << endl;
        cout << "Girl's age: " << age << endl;
    }

    void VisitBoy(Boy& b); //声明Boy类的友元成员函数
    friend void visitBoyGirl(Boy&, Girl&); //声明友元函数
};

void Girl::VisitBoy(Boy& b) {
    cout << "Girl's name: " << name << endl;
    cout << "Girl's age: " << age << endl;
    cout << "Boy's name: " << b.name << endl;
    cout << "Boy's age: " << b.age << endl;
}

class Boy {
private:
    string name;
    int age;
public:
    Boy(string n, int a) : name(n), age(a) {}
    ~Boy() {}

    void Print() {
        cout << "Boy's name: " << name << endl;
        cout << "Boy's age: " << age << endl;
    }

    friend void Girl::VisitBoy(Boy& b); //声明Girl类的友元成员函数
    friend void visitBoyGirl(Boy&, Girl&); //声明友元函数
};

void visitBoyGirl(Boy& b, Girl& g) {
    cout << "Girl's name: " << g.name << endl;
    cout << "Girl's age: " << g.age << endl;
    cout << "Boy's name: " << b.name << endl;
    cout << "Boy's age: " << b.age << endl;
}

int main() {
    Girl girl("ZHOU Yuxing", 16);
    Boy boy("Chen Qi", 15);
    girl.Print();
    boy.Print();
    girl.VisitBoy(boy); //调用Girl类的友元成员函数
    visitBoyGirl(boy, girl); //调用友元函数
    return 0;
}

运行结果：

Girl's name: ZHOU Yuxing
Girl's age: 16
Boy's name: Chen Qi
Boy's age: 15
Boy's name: Chen Qi
Boy's age: 15
Girl's name: ZHOU Yuxing
Girl's age: 16
Boy's name: Chen Qi
Boy's age: 15