#include<iostream.h>

class In;
class Out
{
public:
    Out();
    void fun(Out::In &);

    class In
    {
    public:
        In();
        void fun(Out &);
        friend Out;
    private:
        int i;
    };
    friend In;

private:
    int i;
};

Out::Out()
{
    i=10;
}
void Out::fun(Out::In &a)
{
    cout<<"Out's i="<<i<<endl;
    cout<<"In's i="<<a.i<<endl;
}

Out::In::In()
{
    i=100;
}

void Out::In::fun(Out &a)
{
    cout<<"In's i="<<i<<endl;
    cout<<"Out's i="<<a.i<<endl;
}

int main()
{
    Out a;
    Out::In b;

    a.fun(b);
    b.fun(a);

    return 0;
}

看见就晕了

???????

#include "stdafx.h"
#include<iostream>
using namespace std;
class Out
{
public:
    Out();
    class In
    {
    public:
        In();
        void fun(Out &a);
        friend Out;
    private:
        int i;
    };
    friend In;
    void fun(Out::In &a);

private:
    int i;
};

Out::Out()
{
    i=10;
};
void Out::fun(Out::In &a)
{
    cout<<"Out's i="<<i<<endl;
    cout<<"In's i="<<a.i<<endl;
}

Out::In::In()
{
    i=100;
}

void Out::In::fun(Out &a)
{
    cout<<"In's i="<<i<<endl;
    cout<<"Out's i="<<a.i<<endl;
}

int main()
{
    Out a;
    Out::In b;

    a.fun(b);
    b.fun(a);

    return 0;
}

友元对私有成员访问；类中类；涉及的概念不错。。呵呵

谢谢啊 ,呵呵