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();
     p.show();

     Student stu("lisi",,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",,,"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",,,"math");
     p2->show();

     return ;
 }

程序运行结果：

name:xiayuanquan,age:
name:lisi,age:
score:98.5,subject:English
name:chenglong,age:
score:,subject:chinese
name:zhangsan,age:
score:,subject:math
Program ended with exit code: 

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