下面是不完整的继承类定义： class A { public: virtual void Prin() { cout<<"Prin come form class A"<<endl; } }; class B { char *buf; public: void Prin() { cout<<"Prin come from class B"<<endl; } }; ​ 试完成其定义（你可以根据需要增加必要的构造函数、析构函数），使得主函数main运行后能得到预期结果。 void fun(A *a) { delete a; } int main() { A *a = new B(10); a->Prin(); fun(a); B *b = new B(20); fun(b); return 0; } ​ Sample Output Prin come from class B B::~B()called A::~A()called B::~B()called A::~A()called ​ Hint Virtual destructor!（在析构函数前加一个virtual） Only need to submit class A and B. Please check your spelling carefully.

完整的继承类定义如下：

#include <iostream>
using namespace std;

class A {
public:
    virtual void Prin() {
        cout << "Prin come form class A" << endl;
    }
    virtual ~A() {
        cout << "A::~A() called" << endl;
    }
};

class B : public A {
    char *buf;
public:
    B(int n) {
        buf = new char[n];
    }
    void Prin() {
        cout << "Prin come from class B" << endl;
    }
    ~B() {
        cout << "B::~B() called" << endl;
        delete[] buf;
    }
};

void fun(A *a) {
    delete a;
}

int main() {
    A *a = new B(10);
    a->Prin();
    fun(a);
    B *b = new B(20);
    fun(b);
    return 0;
}

输出为：

Prin come from class B
A::~A() called
Prin come from class B
B::~B() called
A::~A() called