C++类的大小

这是打印不同类别大小的代码

#include <iostream>
using namespace std;
class EmptyClass
{    
};
class AbstractClass
{
  public: 
          virtual void funcOne() = 0;
          virtual void funcTwo() = 0;
};
class NotAbstrClass
{
  public: int virtFunc( int );
};
class MixClass
{
  public:
          virtual void clFunc( int );
          static int i;
          int j;
};
int main()
{
    // Print size of class or class objects
    cout<<"Size of empty class: "<< sizeof(EmptyClass)<<endl;          
    cout<<"Size of Abstract class :"<< sizeof(AbstractClass)<<endl;
    cout<<"Size of Non Abstract class: "<< sizeof(NotAbstrClass)<<endl;
    cout<<"Size of Mix class: "<< sizeof(MixClass)<<endl;
    return 0;
}

C++11编译器上程序的输出是

Size of empty class: 1
Size of Abstract class :4
Size of Non Abstract class: 1
Size of Mix class: 8

我理解为什么Empty类的大小为1空类对象的大小。对于抽象类，对象存储用于实现虚拟函数调用机制的指针。但是其他类对象（NotAbstratrClass和MixClass）的大小呢？