26.虚函数示例理解

Eg1.都没虚函数

#include<iostream>

usingnamespace std;

 

class Father{

public:

    Father(){

        cout <<"this is the Father constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Father is watching tv!"<< endl;

    }

    void say(){

        cout <<"Father is saying!"<< endl;

    }

};

 

class Son :public Father{

public:

    Son(){

        cout <<"this is the Son constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Son is watching tv!"<< endl;

    }

    void say(){

        cout <<"Son is saying!"<< endl;

    }

   

};

 

int main(){

    Father* fa = new Son();

    fa->watchTv();

    fa->say();

    system("pause");

    return 0;

 

}

 

运行结果

 

 

 

解析：因为是Father类型的指针直接调用Father类函数

 

Eg2.子类有虚函数

 

#include<iostream>

usingnamespace std;

 

class Father{

public:

    Father(){

        cout <<"this is the Father constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Father is watching tv!"<< endl;

    }

    void say(){

        cout <<"Father is saying!"<< endl;

    }

};

 

class Son :public Father{

public:

    Son(){

        cout <<"this is the Son constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Son is watching tv!"<< endl;

    }

    virtualvoid say(){

        cout <<"Son is saying!"<< endl;

    }

   

};

 

int main(){

    Father* fa = new Son();

    fa->watchTv();

    fa->say();

    system("pause");

    return 0;

 

}

运行结果：

 

 

 

解析：也是直接调用父类函数

 

Eg3.子类有虚函数

#include<iostream>

usingnamespace std;

 

class Father{

public:

    Father(){

        cout <<"this is the Father constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Father is watching tv!"<< endl;

    }

    virtualvoid say(){

        cout <<"Father is saying!"<< endl;

    }

};

 

class Son :public Father{

public:

    Son(){

        cout <<"this is the Son constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Son is watching tv!"<< endl;

    }

    void say(){

        cout <<"Son is saying!"<< endl;

    }

   

};

 

int main(){

    Father* fa = new Son();

    fa->watchTv();

    fa->say();

    system("pause");

    return 0;

 

}

 

运行结果

 

 

 

解析：Father* fa = new Son()表示在son上Father类型指针，父类有虚函数，就会产生一个虚表，指向该函数，子数也会产生同样一个虚表，不过是指向父类，当主函数执行到fa->say();同于子类重写，父类也跟着重写了，所以是

 

 

。

 

Eg4.子类有虚函数

 

#include<iostream>

usingnamespace std;

 

class Father{

public:

    Father(){

        cout <<"this is the Father constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Father is watching tv!"<< endl;

    }

    virtualvoid say(){

        cout <<"Father is saying!"<< endl;

    }

};

 

class Son :public Father{

public:

    Son(){

        cout <<"this is the Son constructor!"<< endl;

    }

    void watchTv(){

        cout <<"Son is watching tv!"<< endl;

    }

    virtualvoid say(){

        cout <<"Son is saying!"<< endl;

    }

   

};

 

int main(){

    Father* fa = new Son();

    fa->watchTv();

    fa->say();

    system("pause");

    return 0;

 

}

 

运行结果：

 

 

 

解析：

同eg3一样

 

全总结：父类和了类，一般都是先运行父类再运行子数，虚函数只改写子类。