在构造函数与析构函数中调用虚函数（P260）

#include <iostream>
using namespace std;

class A{
public:
virtual void hello()
{
cout<<"A::hello"<<endl;
}
virtual void bye()
{
cout<<"A::bye"<<endl;
}
};

class B:public A
{
public:
virtual void hello()
{
cout<<"B::hello"<<endl;
}
B()
{
hello();
}
~B()
{
bye();
}
};

class C:public B
{
public:
virtual void hello()
{
cout<<"C::hello"<<endl;
}
};

int main()
{
C obj;
return 0;
}