C + + Join me in a thorough understanding of virtual function tables

///First let's understand the order in which class objects are constructed. #include <iostream>using namespace STD;classa{ Public: A () {cout<<"A"<< Endl; }Virtual voidPRINTFA () =0;};classD = Public: B () {cout<<"B"<< Endl; }};classE |Virtual  PublicA Publicb{//About constructing the object order:    The first step is to construct the virtual base class, such as the virtual inheritance here.
 //The second step constructs a generic inheritance class. This runs from left to right.  //The third part constructs member variables, remember that the construction of member variables here is run sequentially.  
 The IV constructs its own constructor.
public: C() { cout << "C" << endl; } void PrintfA() { cout << "hello word!!" << endl; }private:};int main(){ C c; return 0;}

#include <iostream>using namespace STD;typedef void(*pfun) ();classbase{ Public:Virtual voidPrintf () {cout<<"Base::P rintf ()"<< Endl; }voidPrintfbae () {cout<<"Base::P rintfbase"<< Endl; }};classSon1: Publicbase{ Public:Virtual voidPrintf () {cout<<"Son1::P rintf ()"<< Endl; }voidPrintfSon1 () {cout<<"Son1::P rintfSon1 ()"<< Endl; }};classSon2: Publicson1{ Public:voidPrintf () {cout<<"Son2::P rintf ()"<< Endl; }Virtual voidHello () {cout<<"Hello"<< Endl; }voidPrintfSon2 () {cout<<"Son2::P rintf ()"<< Endl; }};intMain () {Son2 s2; Base &b = s2;//b.printf ();    ///Here we can conclude that these three classes maintain a common virtual table, but we have no way of knowing their    Detailed location and the storage relationships of non-virtual functions within each class. So we're going to verify next.
 //pfun fun = (pfun) * ((int *) (& (int*) &b) +1);Pfun fun = (pfun) * ((int*)*(int*)(int*) (&AMP;B) +0);//Such a practice is basically no one to explain, so I explained in the back with the figure. Fun (); Fun = (pfun) * ((int*)*(int*)(int*) (&AMP;B) +1); Fun ();//--------------------------------------------------------Fun = (pfun) * ((int*)*(int*)(int*) (&AMP;S2) +0); Fun (); Fun = (pfun) * ((int*)*(int*)(int*) (&AMP;B) +1); Fun ();//Printing results as above, it is possible to conclude that this virtual table is shared by all of the member classes that have virtual table base classes.  //The generation of each object must have two data. A vptr pointer to a virtual table, and its own members //variable. 
 return 0;} //Summary 1: The premise is that the base class is a virtual table, single inheritance, all the member classes and the base class together maintain the same virtual table, each has //A vptr points to this virtual table, the subclass assumes that the virtual table will be replaced, in detail depending on whether the subclass has overloaded the base class //virtual function to determine that we become covered. 
多继承以下讨论，事实上本质是一样的，关键问题是，多继承中//子类中究竟有几份虚vptr指针。

#include <iostream>using namespace STD;classa{ Public:Virtual voidPrintf () {cout<<"A::P rintf ()"<< Endl; }Virtual voidPRINTFA () {cout<<"A::P RINTFA ()"<< Endl; }};classb{ Public:Virtual voidPRINTFB () {cout<<"B::P rintf ()"<< Endl; }Virtual voidPrintf () {cout<<"B::P rintf ()"<< Endl; }};classE | PublicA Publicb{ Public:voidPrintf () {cout<<"C::P rintf ()"<< Endl; }};intMain () {typedef void(*pfun)    ();    c C; Pfun fun = (pfun) * ((int*)*(int*)((int*) (&AMP;C) +0) +0);The first virtual table pointer vptr.
Fun (); //Covered here. The call is printf () in C; fun = (pfun) * ((int *) * (int *) (int *) (&C) + 1) + 0< /c10>); //Second virtual table pointer vptr. Fun (); //The other highlight here is why (int *) (int *) two times. You should be clear about that. Because there may //have more than one virtual pointer. The compiler is doing very well, assuming that compiling without this will cause an error.  
 cout << sizeof(c) << Endl; //Ultimate test Result 8.  return 0;} //Summary 2: Each base class in multiple inheritance maintains one of its own virtual tables, and each inheritance of a virtual base class in a subclass has a //Pointer to the base class virtual table, the above code tests the result that there are two vptr pointers in the C object. A virtual table that points to a base class, one //A virtual table that points to the B-base class.  

C + + Join me in a thorough understanding of virtual function tables