c++之虚函数virtual , overriding , overwrite

先来看下普通的继承：

class Instrument{
public:
    void play() const{
        cout<<"Instrument::play"<<endl;
    }
};

class Wind : public Instrument{
public:
    void play() const{
        cout<<"Wind::play"<<endl;
    }
};

    Instrument* instrumentObj = new Instrument();
    instrumentObj->play();        //output: Instrument::play

    Wind* windObj = new Wind();
    windObj->play();            //output: Wind::play

    Instrument* windInsObj = new Wind();    //子类对象指向父类的指针
    windInsObj->play();            //output: Instrument::play

    //Wind* InsWindObj = new Instrument();// wrong !父类对象不能指向子类的指针    

以下是虚函数的继承：

class Instrument{
public:
    virtual void play() const{
        cout<<"Instrument::play"<<endl;
    }
};

class Wind : public Instrument{
public:
    void play() const{
        cout<<"Wind::play"<<endl;
    }
};
　　Instrument* instrumentObj = new Instrument();
    instrumentObj->play();        //output: Instrument::play

    Wind* windObj = new Wind();
    windObj->play();            //output: Wind::play

    Instrument* windInsObj = new Wind();    //子类对象指向父类的指针
    windInsObj->play();            //output: Wind::play

    //Wind* InsWindObj = new Instrument();// wrong !父类对象不能指向子类的指针

纯虚函数和抽象类

纯虚函数使用关键字virtual 并在函数最后加上=0.eg:virtual void fun()=0;