c – 通过对基类的引用来调用虚函数

当我运行它时,此代码拒绝将适当的消息打印到控制台.使用指针而不是引用似乎可行( – >而不是.).我是OOP的新手,请原谅我,如果你觉得这太荒谬了.

#include <iostream>

using namespace std;

class instrument {
public:
    virtual void play(){}
};

class drum : public instrument {
public:
    void play(){
        cout << "dum,dum" << endl;
    }
};

class piano : public instrument {
public:
    void play(){
        cout << "pling" << endl;
    }
};

int main (){
    instrument i;
    piano p;
    drum d;

    instrument &pi = i;
    pi.play();  // -

    pi = p;
    pi.play();  // pling

    pi = d;
    pi.play();  // dum,dum
}

instrument &pi = i;

pi = p;

instrument &pi = i;
pi.play();  // -

instrument &pp = p;
pp.play();  // pling

instrument &pd = d;
pd.play();  // dum,dum