C++析构函数需要加virtual

#include<iostream>  
using namespace std;  

class Base  
{  
public:  
    Base() 
    {
        cout << "base" << endl;
    } //Base的构造函数  
    virtual ~Base() //Base的析构函数  
    {  
        cout << "~Base!" << endl;  
    } 
};  

class Derived : public Base  
{  
public:  
    Derived() 
    {
        cout << "drived" << endl;
    } //Derived的构造函数  
    ~Derived() //Derived的析构函数  
    {  
        cout << "~Derived!" << endl;  
    }   
};  
/*基类要用virtual的原因*/
int main()  
{  
    Derived *pTest1 = new Derived(); //Derived类的指针  
    delete pTest1;  

    cout << endl;  

    Base *pTest2 = new Derived(); //Base类的指针  
    delete pTest2;  

    return 0;  
}