OJ：析构函数实现多态

Description

下面程序的输出结果是：

destructor B

destructor A

请完整写出 class A。 限制条件：不得为 class A 编写构造函数。

#include <iostream>
using namespace std;

class A {
// Your Code Here
};

class B:public A {
    public:
        ~B() { cout << "destructor B" << endl; }
};

int main() {
    A * pa;
    pa = new B;
    delete pa;
    return 0;
}

实现代码

#include <iostream>
using namespace std;

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

class B:public A {
    public:
        ~B() { cout << "destructor B" << endl; }
};

int main() {
    A * pa;
    pa = new B;
    delete pa;

    return 0;
}