为什么这个程序中sizeof的结果是4？请高手指教
#include<iostream>
#include<complex>

using namespace std;
class base
{
public:
    base(){cout<<"base-ctor"<<endl;}
    ~base(){cout<<"base-dtor"<<endl;}
    virtual void f(int){cout<<"base::f(int)"<<endl;}
    virtual void f(double){cout<<"base::f(double)"<<endl;}
    virtual void g(int i=10){cout<<"base::g()"<<i<<endl;}
    void g2(int i=10){cout<<"base::g2"<<i<<endl;}
};
class derived:public base
{
public:
    derived(){cout<<"derived-ctor"<<endl;}
    ~derived(){cout<<"derived-dtor"<<endl;}
    void f(complex<double>){cout<<"derived::f(complex)"<<endl;}
    virtual void g(int i=20){cout<<"derived::g()"<<i<<endl;}
};
void main()
{
    base b;
    derived d;
    base *pb=new derived;
    cout<<sizeof(base)<<"tt"<<endl;
    cout<<sizeof(derived)<<"bb"<<endl;
}

请看下面的定义(主要是定议的类"大"了点,我来个"小"点的)
   class A{
      virtul ~A(){}
   }
  sizeof(A)=4 ? 你问的实际就是这个问题.
不知道你了不了解C++多态的实现方式?看没有看过一本书<<Inside the C++ Object Model>>里面讲的很清楚.
 当一个类中有虚函数存在时,编译器为自动为我个类加上一个成员(对于程序员来说,是透明的)vptr,也就是虚表指针.它指向一个虚表,表中存放的时类的虚函数地址,用于实现C++的动态绑定.

我这里只是简单说了一下,如果想了解更加详细的内容还请看Inside the C++ Object Model这本书.

谢谢楼上的