以下是引用gwcome在2013-3-17 15:02:54的发言：

//自己写着玩的，是关于友元函数
#include<iostream>
class Lovers
{
   
public:
    void kiss_action();
protected:
    void kiss();
private:
   
};

class Girlfriend :public Lovers
{
friend class Others;   
public:
    void kiss_action();
protected:
    void kiss();
   
private:
   
};

class Boyfriend :public Lovers
{
public:
    void kiss_action();
protected:
    void kiss();
private:
};

class Others
{
   
public:
    void kiss_other();
protected:
   
private:
};

void Lovers::kiss()
{
    std::cout<<"I want kiss";
}

void Lovers::kiss_action()
{
    Lovers::kiss();
}

void Girlfriend::kiss()
{
    Lovers::kiss_action();
    std::cout<<"my girlfriend  I am a normal boy";
}

void Girlfriend::kiss_action()
{
    Girlfriend::kiss();
}

void Boyfriend::kiss()
{
    Lovers::kiss_action();
    std::cout<<"my boyfriend  I am a gayboy";
}

void Boyfriend::kiss_action()
{
    Boyfriend::kiss();
}

void Others::kiss_other()
{
    Girlfriend::kiss();//“Girlfriend::kiss_action”: 非静态成员函数的非法调用
    std::cout<<"I am a third..hehe";
}
int main()
{
    Lovers lovers;//定义对象 ...TAT...
    lovers.kiss_action();
    Girlfriend girlfriend;
    girlfriend.kiss_action();
    Boyfriend boyfriend;
    boyfriend.kiss_action();
    Others others;
    others.kiss_other();
    return 0;
}
我定义了对象  还是有错

#include "stdafx.h"
//自己写着玩的，是关于友元函数
#include<iostream>
class Lovers
{

public:
    void kiss_action();
protected:
    void kiss();
private:

};

class Girlfriend :public Lovers
{
    friend class Others;    
public:
    void kiss_action();
protected:
    void kiss();

private:

};

class Boyfriend :public Lovers
{
public:
    void kiss_action();
protected:
    void kiss();
private:
};

class Others
{

public:
    void kiss_other();
protected:

private:
};

void Lovers::kiss()
{
    std::cout<<"I want kiss";
}

void Lovers::kiss_action()
{
    Lovers::kiss();
}

void Girlfriend::kiss()
{
    Lovers::kiss_action();
    std::cout<<"my girlfriend  I am a normal boy";
}

void Girlfriend::kiss_action()
{
    Girlfriend::kiss();
}

void Boyfriend::kiss()
{
    Lovers::kiss_action();
    std::cout<<"my boyfriend  I am a gayboy";
}

void Boyfriend::kiss_action()
{
    Boyfriend::kiss();
}

void Others::kiss_other()
{
    Girlfriend girl;
    girl.kiss();
    std::cout<<"I am a third..hehe";
}
int main()
{
    Lovers lovers;//定义对象 ...TAT...
    lovers.kiss_action();
    Girlfriend girlfriend;
    girlfriend.kiss_action();
    Boyfriend boyfriend;
    boyfriend.kiss_action();
    Others others;
    others.kiss_other();
    return 0;
}