1.C++ Virtual 用法

这里只讲语法，因为讲原理比较难。还没有涉及到构造函数。那么就直接上代码了：

// VitualFunction.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include
#include

using namespace std;
//base class
class Animal{
public:
virtual void eat(){
cout << "animal eat" << endl;
}
virtual void die(){
cout << "animal die" << endl;
}
};

class Dog : public Animal{
public:
void eat(){
cout << "dog eat" << endl;
 Animal::die();//use base class's function
}
};

class Cat : public Animal{
public:
void eat(){
cout << "cat eat" << endl;
}
};

class Lion : public Animal{

};

int _tmain(int argc, _TCHAR* argv[])
{
vector someAnimals;
someAnimals.push_back(new Animal());
someAnimals.push_back(new Dog());
someAnimals.push_back(new Cat());
someAnimals.push_back(new Lion());

for(int i = 0; i < someAnimals.size(); ++i){
someAnimals[i]->eat();
}

system("pause");
return 0;
}

我总是觉得C++的这块语法有点不对，因为我是先搞过C#和Java的。当子类重写父类方法时，连个关键词都没有，就重写了。还有调用父类的方法，连个关键词都没有，直接名字加::就调用了，也太不尊重父类了。这可能是C++支持多重继承的语法决定。

2.C#中的virtual用法

using System;
using System.Collections.Generic;

using System.Text;

namespace VirutalFunctionCShape
{
//base class
 public class Animal{
public virtual void eat(){
Console.WriteLine("Animal eat");
}
public virtual void die(){
Console.WriteLine("Animal die");
}
}

public class Dog : Animal{
public override void eat()
{
Console.WriteLine("Dog eat");
base.die();
}
}

public class Cat : Animal{
public override void eat()
{
Console.WriteLine("Cat eat");
}
}

public class Lion : Animal{

}

class Program
{
static void Main(string[] args)
{
IList someAnimals = new List();
someAnimals.Add(new Animal());
someAnimals.Add(new Dog());
someAnimals.Add(new Cat());
someAnimals.Add(new Lion());

foreach (Animal animal in someAnimals)
{
animal.eat();
}

Console.ReadLine();
}
}
}

C#中比C++好多了，重写的时候加上了override关键词，调用父类的方法时候加上了base关键词。