[C++] Virtual Destructor(虚析构函数)

class A{

public:
    int a = 3;
    A()
    {
        cout <<"A()..."<< endl;
    }
     ~A()
    {
        cout << "~A()..." << endl;
    }
};
class B : public A{
public:
    int b;
    B(){
        cout << "B()..." << endl;
    }
    ~B(){
        cout << "~B()..." << endl;
    }
};
void main()
{
    A *a = new B;
    delete a;
    system("pause");
}
result:

A()...
B()...
~A()...
Press any key to continue . . . 
没有~B（），内存泄漏！！

class A{

public:
    int a = 3;
    A()
    {
        cout <<"A()..."<< endl;
    }
    virtual ~A()
    {
        cout << "~A()..." << endl;
    }
};
class B : public A{
public:
    int b;
    B(){
        cout << "B()..." << endl;
    }
    ~B(){
        cout << "~B()..." << endl;
    }
};
void main()
{
    A *a = new B;
    delete a;
    system("pause");
}

result:

　A()...
　B()...
　~B()...
　~A()...
　Press any key to continue . . .

防止内存泄漏！！