先上代碼吧，不相干的省略

#include?<iostream>
#include?<typeinfo>
using?namespace?std;

class?Fly{
public:
	//virtual?void?fly()=0;
};

class?Bird:public?Fly{
public:
	/*virtual?void?fly(){
		cout<<"i?am?a?bird,i?can?fly"<<endl;
	}*/
};

class?Plane:public?Fly{
public:
	/*virtual?void?fly(){
		cout<<"i?am?a?plane,i?can?fly!"<<endl;
	}*/
};


void?doSomething(Fly?*f){
	cout<<"i?am?"<<typeid(*f).name()<<endl;
}

int?main(){
	Fly?*f=new?Plane();
	doSomething(f);
	delete?f;
	f=NULL;

	Bird?b;
	doSomething(&b);
	return?0;
}

打印結(jié)果是

i am 3Fly

i am 3Fly

而把類底下的注釋取消，打印結(jié)果是

i am 5Plane

i am 4Bird

這里的3 4 5是什么 ?怎么來的？