只有基类的析构函数需要为虚函数

//
//  main.cpp
//  TescDtor
//
//  Created by Jiacan Li on 6/16/17.
//  Copyright © 2017 Jiacan Li. All rights reserved.
//

#include <iostream>
using namespace std;

class ClxBase1
{
public:
    ClxBase1()
    {
    }
    
    virtual ~ClxBase1()
    {
        cout<<"~ClxBase1"<<endl;
    }
};

class ClxBase2 : public ClxBase1
{
public:
    ClxBase2()
    {
    }
    
    ~ClxBase2()
    {
        cout<<"~ClxBase2"<<endl;
    }
};

class ClxDerived : public ClxBase2
{
public:
    ClxDerived()
    {
        
    }
    
    ~ClxDerived()
    {
        cout << "~ClxDerived" << endl;
    }
};

int main(int argc, const char * argv[])
{
    ClxBase1* cp = new ClxDerived();
    delete cp;
    int i = 0;
}