Object Layout in C + +

When a virtual table is involved in C + +, the layout of the class object is divided into: virtual table and data member, subclass contains derived class layout, assume the following program:

1#include <iostream>2 3 using namespacestd;4 5 classB {6 Private:7     intA;8  Public:9 B () {TenA = One; One     } A  -     Virtual voidFun () { -cout <<"B::fun"<<Endl; the     } - }; -  - classA: PublicB { +  Public: - A () { +cout <<"class A Constructor"<<Endl;  Am =3; atn =2; -     } -  -~A () { -cout <<"~a ()"<<Endl; -     } in     Virtual voidFun () { -cout <<"A::fun"<<Endl; to     } +  - Private: the     intM,n; * }; $ Panax Notoginseng intMainintargcChar*argv[]) - { the A; +     int*p; Atypedefvoid(*pf_t) (void); the      + pf_t PF; -p = static_cast<int*> ((int*) &a); $PF =(pf_t) p; $      -     int*vptr = * (int* *) &A; -     int*vtable = (int*)*vptr; thePF = (pf_t) vtable[2]; - Wuyiprintf"address A::fun%p\n", pf); the  -cout <<"P:"<< *p <<Endl; WuP + + ; -cout <<"P:"<< *p <<Endl; Aboutp++; $cout <<"P:"<< *p <<Endl; -p++; -cout <<"P:"<< *p <<Endl; -          Ap++; +cout <<"P:"<< *p <<Endl; the  -  $     return 0; the}

With the VS 2010 Display Object Layout diagram (cl-d1reportallclasslayout), where meta is the type information for the corresponding object:

Class B:

1 class B    Size (8):  2     +--- 3  0    |  {VFPTR} 4  4    | a 5     +--- 6  7b::[email protected]:  8     | &B_meta  9      |  0 Ten  0    | &b::fun

Class A:

 class  A size (16  ):    +---    | +---(base  class   B)  0  | |  {vfptr}  4  | |  a  | +---8  |  M  12  |  n  +---a::[email protected]:  |  &a_meta  | 0  0  | &a::funa::fun  0  

Object Layout in C + +