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; } }; 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：

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

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

在类A中增加了一个虚析构函数，并且将类B继承自类A，同时在类B的构造函数中增加了一个动态内存分配的操作，因为需要在析构函数中释放这个动态内存。在类B的析构函数中增加了一个输出语句，用来验证析构函数的调用。这样，主函数中的代码就能够正确运行并输出预期结果了。

相关问题

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

下面是完整的继承类定义：

#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 size) {
        buf = new char[size];
    }
    void Prin() {
        cout << "Prin come from class B" << endl;
    }
    ~B() {
        delete[] buf;
        cout << "B::~B() called" << endl;
    }
};

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;
}

输出结果：

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

abstract class MyPoint { public abstract void show(); } //打印正方形 class MyPrintSquare extend MyPoint { @Override public void show() { for(int i=0;i<=5;++i){ for(int j=1;j<=5;++j){ if(j==1 && j==4) Systemout.print('*'); if(i==0 && i==4) System.out.print('*'); else Sytem.out.print(' '); } } } } //打印圆形 class MyPrintCircle extends MyPoint{ @Override public void show() { for (int y = 0; y <2 * 5; y += 2) { int x = (int)Math.round(5 - Math.sqrt(2 * 5 * y - y * y)); int len = 2 * (5 - x); for (int i = 0; i <= x; i++) { System.out.print(' '); } System.out.print('*'); for (int j = 0; j < len; j++) { System.out.prin(' '); System.out.println('*'); } } } } public class MyPointTest { public static void Show(MyPoint a){ a.Show(); } public static void main(String[] args){ MyPoint mp1 = new MyPrintSquare(); MyPoint mp2 = new MyPrintCircle(); myShow(mp1); myShow(mp2); } }

这段代码存在几个错误，可能是因为笔误或者拼写错误。下面是我发现的错误和建议的修改：

1. 在类 MyPrintSquare 的 extends 后应该是 MyPoint，而不是 extend MyPoint。
2. 在 MyPrintSquare 的 show 方法中，System.out.print('*') 和 System.out.prin(' ') 中间的字母 t 应该是少打了一个。
3. 在 MyPrintCircle 的 show 方法中，System.out.prin(' ') 应该是 System.out.print(' ')。
4. 在 MyPointTest 的 main 方法中，myShow 应该是 Show。

下面是修改后的代码：

abstract class MyPoint {
    public abstract void show();
}

//打印正方形
class MyPrintSquare extends MyPoint {
    @Override
    public void show() {
        for(int i=0;i<=5;++i){
            for(int j=1;j<=5;++j){
                if(j==1 || j==4)
                    System.out.print('*');
                if(i==0 || i==4)
                    System.out.print('*');
                else System.out.print(' ');
            }
            System.out.println();
        }
    }
}

//打印圆形
class MyPrintCircle extends MyPoint{
    @Override
    public void show() {
        for (int y = 0; y <2 * 5; y += 2) {
            int x = (int)Math.round(5 - Math.sqrt(2 * 5 * y - y * y));
            int len = 2 * (5 - x);
            for (int i = 0; i <= x; i++) {
                System.out.print(' ');
            }
            System.out.print('*');
            for (int j = 0; j < len; j++) {
                System.out.print(' ');
                System.out.print('*');
            }
            System.out.println();
        }
    }
}

public class MyPointTest {
    public static void Show(MyPoint a){
        a.show();
    }
    public static void main(String[] args){
        MyPoint mp1 = new MyPrintSquare();
        MyPoint mp2 = new MyPrintCircle();
        Show(mp1);
        Show(mp2);
    }
}