C++：C++的两种多态形式

//
//  main.cpp
//  Test.cpp
//
//  Created by mac on 15/8/11.
//  Copyright (c) 2015年. All rights reserved.
//
#include<iostream>
#include<cstring>
using namespace std;
class Person    //基类Person
{
private:
    string  name;
    int age;
public:
    Person();
    virtual ~Person();//虚析构函数
    Person(string name,int age);
    void setname(string name);
    void setage(int age);
    virtual void show();//虚成员函数,子类继承后必须要重写该函数
    //virtual void show()=0;//纯虚函数,此时该类就不能创建对象了。
};
Person::Person(){};
Person::Person(string name,int age)
{
    this->name = name;
    this->age = age;
}
void Person::setname(string name)
{
    this->name = name;
}
void Person::setage(int age)
{
    this->age = age;
}
void Person::show()
{
    cout<<"name:"<<name<<","<<"age:"<<age<<endl;
}
Person::~Person(){};
class Student:public Person//基类Person的公有派生类Studnet
{
private:
    float score;
    string subject;
public:
    Student();
    virtual ~Student();//virtual可加可不加
    virtual void show();//virtual可加可不加
    Student(string name,int age,float score,string subject);
};
Student::Student(){};
Student::Student(string name,int age,float score,string subject):Person(name,age)
{
    this->score = score;
    this->subject = subject;
}
void Student::show()
{
    Person::show();
    cout<<"score:"<<score<<","<<"subject:"<<subject<<endl;
}
Student::~Student(){};
int main(int argc, const char * argv[])
{
    Person p;
    p.setname("xiayuanquan");
    p.setage(23);
    p.show();
    
    Student stu("lisi",23,98.5,"English");
    stu.show();
    
    //多态的特性(例1)父类的引用指向子类对象
    Person person;
    Student st("chenglong",60,99,"chinese");
    person = st;
    st.show();
    
    //多态的特性(例2)父类的指针指向子类对象
    Person *p2 = new Student("zhangsan",20,100,"math");
    p2->show();
    
    return 0;
}

   程序运行结果：

name:xiayuanquan,age:23
name:lisi,age:23
score:98.5,subject:English
name:chenglong,age:60
score:99,subject:chinese
name:zhangsan,age:20
score:100,subject:math
Program ended with exit code: 0

总结：实现多态的三个条件：

1.存在继承关系

2.多态的第一种,父类的引用指向子类对象 或者 多态的第二种,父类的指针指向子类对象。

3.子类必须要重写父类的同名方法