析构函数是虚函数时

#include <iostream>
#include <cstring>
using namespace std;
class A{
public:
	A(){ p(); }
	virtual void p(){ cout << "a" << endl; }
	 ~A(){ p(); }
};
class B :public A{
public:
	B(){ p(); }
	void p(){ cout << "B" << endl; }
	~B(){ p(); }
};
int main(int, char**){
	A* a = new B();
	
	delete a;// a  B  a  此时派生类没有被释放
	cout << "********" << endl;
	B *b = new B();
	delete b;// a  B B a   当释放派生类时，先释放基类，后释放派生类。
	return 0;
}

给A类中析构函数是虚函数时

#include <iostream>
#include <cstring>
using namespace std;
class A{
public:
	A(){ p(); }
	virtual void p(){ cout << "a" << endl; }
	virtual ~A(){ p(); }
};
class B :public A{
public:
	B(){ p(); }
	void p(){ cout << "B" << endl; }
	~B(){ p(); }
};
int main(int, char**){
	A* a = new B();	
	delete a;            // a  B B a 
	cout << "********" << endl;
	B *b = new B();
	delete b;
	return 0;
}

#include <iostream>
#include <cstring>
using namespace std;
class A{
public:
	A(){ p(); }
	virtual void p(){ cout << "a" << endl; }
	virtual ~A(){ p(); }
};
class B :public A{
public:
	B(){ p(); }
	void p(){ cout << "B" << endl; }
	~B(){ p(); }
};
int main(int, char**){
	cout << "********" << endl;
	A c;                    //a
	cout << "********" << endl;
	B d;                   // a B
	cout << "********" << endl;
	A* a = new B();        //a B
	delete a;              //B a
	cout << "********" << endl;
	B *b = new B();        //a B
	delete b;              //B a
	return 0;              // B a(先释放d对象的析构)  a（再释放c对象的析构）
}

// 其中 对象c、d是在return 0时释放的。