虚函数，纯虚函数 -- 动物吃什么

#include "stdafx.h"
#include
using namespace std;

class animal
{
public:
 virtual void eat() = 0;
};

class bird : public animal
{
public:
 virtual void eat();
};

class beast: public animal
{
public:
 virtual void eat();
};

class cock:public bird
{
public:
 virtual void eat();
};

class duck:public bird
{
public:
 virtual void eat();
};

class horse:public beast
{
public:
 virtual void eat();
};

class cat:public beast
{
public:
 virtual void eat();
};

void animalEatWhat(animal* a_animal)
{
 a_animal->eat();
}

void bird::eat()
{
 cout<<"bird is eating some small thing"<}

void beast::eat()
{
 cout<<"beast is eating some big thing"<}

void cock::eat()
{
 cout<<"cock is eating bread"<}

void duck::eat()
{
 cout<<"duck is eating fish"<}

void horse::eat()
{
 cout<<"horse is eating grass"<}

void cat::eat()
{
 cout<<"cat is eating moss"<}

 

int _tmain(int argc, _TCHAR* argv[])
{
 bird a_bird;
 beast a_beast;
 cock a_cock;
 duck a_duck;
 horse a_horse;
 cat  a_cat;

 animalEatWhat(&a_bird);
 animalEatWhat(&a_beast);
 animalEatWhat(&a_cock);
 animalEatWhat(&a_duck);
 animalEatWhat(&a_horse);
 animalEatWhat(&a_cat);

 return 0;
}

 

1、这里用到了虚函数，和纯虚函数。虚函数、多态、动态联编是一个概念。

2、为什么要用多态呢？ 多态是C++典型的特性，最大的好处的接口的通用化。我们这里的一个接口animalEatWhat(animal* a_animal)，就可以给6个不同的类来使用。 而不需要去写六个类似的函数。

3、虚函数纯粹作为接口，只声明不定义。虚函数可以声明可以定义。

4、程序的运行结果如下：

bird is eating some small thing
beast is eating some big thing
cock is eating bread
duck is eating fish
horse is eating grass
cat is eating moss
请按任意键继续. . .