OJ：析構函數實現多態

Description

下麵程式的輸出結果是：

destructor B

destructor A

請完整寫出 class A。 限制條件：不得為 class A 編寫構造函數。

#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;
}

實現代碼

#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;
}