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:

巴特西

C++ 中的对象布局

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