C++ 中的对象布局

C++中的涉及到虚表时，类对象的布局分为：虚表与数据成员，子类包含派生类布局，假设下面一个程序:

 #include <iostream>

 using namespace std;

 class B {
 private:
     int a;
 public:
     B() {
         a = ;
     }

     virtual void fun() {
         cout << "B::fun" << endl;
     }
 };

 class A:public B {
 public:
     A() {
         cout << "class A constructor" << endl;
         m = ;
         n = ;
     }

     ~A() {
         cout << "~A()" << endl;
     }
     virtual void fun() {
         cout << "A::fun" << endl;
     }

 private:
     int m,n;
 };

 int main(int argc, char *argv[])
 {
     A a;
     int *p;
     int **pvtr = (int **)&a;

     typedef void (*pf_t)();

     pf_t pf;
     p = static_cast<int *>((int *)&a);

     pf = (pf_t)(pvtr[][]);
     pf();
     //cout << "*pf:" << *pf << ",pf:" << pf << endl;

     //(*(*pf+sizeof(void*) * 2))();

     cout << "p:" << *p << endl;
     p ++ ;
     cout << "p:" << *p << endl;
     p++;
     cout << "p:" << *p << endl;
     p++;
     cout << "p:" << *p << endl;

     p++;
     cout << "p:" << *p << endl;

     return ;
 }

通过VS 2010显示对象布局图(cl -d1reportAllClassLayout)，其中meta为对应对象的类型信息:

类B:

 class B    size():
     +---
      | {vfptr}
      | a
     +---

 B::$vftable@:
     | &B_meta
     |
      | &B::fun

类A:

class A    size():
    +---
    | +--- (base class B)
     | | {vfptr}
     | | a
    | +---
     | m
    | n
    +---

A::$vftable@:
    | &A_meta
    |
     | &A::fun

A::fun this adjustor: