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。那么直接上代码了：
// VitualFunction.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
#include <vector>
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<Animal*> 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;
}