再問有關(guān)友元和繼承的一些問題

cir2633

以前的帖子沒搞明白:http://topic.csdn.net/u/20091204/16/440ccc4a-9a49-401a-984f-06f787a8aa3b.html?seed=1506412902&r=61706661#r_61706661

//--問題如下----------------------------------

class Base{
        friend class Frnd;
public:
        int pub_val;
protected:
        int pro_val;
private:
        int pri_val;
};

class public_derived : public Base {
};

class protected_derived : protected Base {
};

class private_derived : private Base {
};

class Frnd{
public:
        int i;
        int mem1(protected_derived d) {return d.pub_val;}  //-1
        int mem2(protected_derived d) {return d.pro_val;}  //-2
//      int mem3(protected_derived d) {return d.pri_val;}
//      int mem1(private_derived d) {return d.pub_val;}
//      int mem2(private_derived d) {return d.pro_val;}
//      int mem3(private_derived d) {return d.pri_val;}

};
被注釋掉的是錯誤的地方, 但是標(biāo)注1和2可以編譯過,
Frnd是Base的友元,友元關(guān)系不得繼承;
所以Frnd不是public_derived類的友元,但是Frnd卻訪問了public_derived類的protected和private成員,
我有點不理解