C++中虚拟函数的内存分配机制是什么

//#include<stdio.h>

#include<iostream>
using namespace std;

class CMem	
{
	
public:
 CMem(){}
public:
 int m_first;
private:
 unsigned char m_second;
 
public :
 void fun1();
 virtual int funOver(){return 1;}
 
};



class CMemSub : public CMem
{

public:
 CMemSub(){}

public:
 int m_three;

private:
 int m_four;
 
public:
 void fun3();
 virtual int funOver(){return 2;}

virtual int fun4(){return 3;}


};


int main()
{ 
 CMem a,*pMem;
 CMemSub b;
  pMem = &a;
 printf("%d/n",pMem->funOver());
 
  pMem = &b;
  printf("%d/n",pMem->funOver());

 
	
	return 0;
}