多继承时，多个基类中存在型别相同的虚函数，该怎么做？

#include "stdafx.h"
#include<iostream>

using namespace std;

class A{
public:
    virtual void show(){
        cout<<"in classA"<<endl;
    }
    virtual ~A(){}
};

class B{
public:
    virtual void show(){
        cout<<"in classB"<<endl;
    }
    virtual ~B(){}
};

class MidA:public A{
public:
    virtual void realshowA() = 0;
    virtual void show(){
        realshowA();
    }
//    virtual ~MidA(){}
};
class MidB:public B{
public:
    virtual void realshowB() = 0;
    virtual void show(){
        realshowB();
    }
//    virtual ~MidB(){}
};

class Derive :public MidA,public MidB{
public:
    void realshowA(){
        cout<<"realshow in classA"<<endl;
    }
    void realshowB(){
        cout<<"realshow in classB"<<endl;
    }
//    virtual ~Derive(){}
};

int main(int argc,char * argv){
    A *pa= new Derive;
    B *pb= new Derive;
    pa->show();
    pb->show();

    delete pa;
    delete pb;

    return 0;
}

只要基类声明为析构函数，派生类的所有析构函数自然也为虚函数。参考effective C++ 条款07