c++ - Accessing private virtual functions within same class -

i asked, using code , writing in extractmultadd() function, return variable.x variable.y variable.add() , variable.multiply. understand basic concept of virtual tables , when created, despite best efforts, i'm not quite sure how leverage them access private virtual functions. appreciated.

#include <cstdio> #include <iostream> class multadd {  private:     int x;     int y;     virtual int add()   //virtual fuction vtable created thing class     {             return x+y;     }     virtual int multiply()     {             return x*y;     } public:     multadd(){             x = 2;             y = 10;     } };  int extractmultadd(void* math) {     return 0; }  int main() {     multadd variable;     printf("%d\n", extractmultadd(&variable));     return 0; } 

i give 2 versions choose. not follow standard, , no means portable, both work on msvc 2013, gcc 4.9, , clang 3.5 test it. second version relatively safer , more portable first one. in fact, expect rather robust.

version 1:

#include <iostream>  class multadd { private:   int x;   int y;   virtual int add() { return x + y; }   virtual int multiply() { return x * y; } public:   multadd() {     x = 2;     y = 10;   } };  struct multaddcracker: multadd {   int add();   int multiply(); };  void extractmultadd(multadd& v) {   char* p = (char*)&v;   std::cout << *(int*)(p + sizeof(void*)) << '\n';   std::cout << *(int*)(p + sizeof(void*) + sizeof(int)) << '\n';   multaddcracker* pcracker = (multaddcracker*)&v;   std::cout << pcracker->add() << '\n';   std::cout << pcracker->multiply() << '\n'; }  int main() {   multadd v;   extractmultadd(v); } 

version 2:

#include <iostream>  class multadd { private:   int x;   int y;   virtual int add() { return x + y; }   virtual int multiply() { return x * y; } public:   multadd() {     x = 2;     y = 10;   } };  struct multaddcracker {   int x;   int y;   virtual int add();   virtual int multiply(); };  void extractmultadd(multadd& v) {   multaddcracker& w = (multaddcracker&)v;   std::cout << w.x << '\n';   std::cout << w.y << '\n';   std::cout << w.add() << '\n';   std::cout << w.multiply() << '\n'; }  int main() {   multadd v;   extractmultadd(v); }