c++マルチステートマルチインスタンス

#include 
using namespace std;
class A
{
public:
    A()
    {
        cout << "  A" << endl;
        s = new char[20];
        memset(s, 0, 20);
        strcpy(s, "hahaha");
    }
    virtual ~A()
    {
        cout << "  A" << endl;
        delete []s;
    }
    virtual void print()
    {
        cout << s << endl;
    }
private:
    char *s;
};
class B :  public A
{
public:
    B()
    {
        cout << "  B" << endl;
        s = new char[20];
        memset(s, 0, 20);
        strcpy(s, "BBBBB");
    }
    virtual ~B()
    {
        cout << "  B" << endl;
        delete []s;
    }
    virtual void print()
    {
        cout << s << endl;
    }
private:
    char *s;
};

void ok(A *obj)
{
    obj->print();
}
void okk(A obj)
{
    obj.print();

}

1.

int main()
{
    B *b = new B;
    A *obj = b;
    obj->print();
    delete b;
    
    /*  A
      B
    BBBBB
      B
      A*/
}

2.

int main()
{
    B *b = new B;
    A *obj = b;
    obj->print();
    delete obj;

    /*  A
      B
    BBBBB
      A*/
}

3.

int main()
{
    B b;
    A a = b;
    A *pa = &b;
    a.print();//   a    A     ，               B   A ，         ，       A     。
    pa->print();//      ，      A，             B       ，          A  ，        Test  B   

    /*  A
      B
    hahaha
    BBBBB
      A
      B
      A*/
}

4.

int main()
{
    B *b = new B;
    ok(b);

    /*  A
      B
    BBBBB*/
}

5.

int main()
{
    B *b = new B;
    ok(b);
    delete b;
    
    /*  A
      B
    BBBBB
      B
      A*/
}

6.

int main()
{
    B b;
    okk(b);

    /*  A
      B
    hahaha
      A
      B
      A*/
}

7.

int main()
{
    B *b = new B;
    A a;
    b = &a; //  ，            
    ok(b);
}

転載先:https://www.cnblogs.com/lesroad/p/10778121.html