c++ - Virtual function acting weird in inheritance? -

lemme explain problem giving example:

#include <iostream>  class pc { public:     pc():data(0)     {     }     virtual void display()     {         std::cout<<"the data :"<<data<<std::endl;     } protected:     int data; };  class smartpc:private pc { public:     smartpc():pc()     {     }     void convert()     {         pc* temp=static_cast<pc*>(this);         temp->display();     }     void display()     {         std::cout<<"the data (in bb):"<<a<<std::endl;     } };  int main() {     smartpc smrtpc;     pc* minipc= static_cast<pc*>(&smrtpc);     smrtpc.convert(); } 

according scott meyers : static_cast<pc*>(this); create temp base copy of smartpc. temp->display(); executed display() function of derived class. why so? shouldn't execute function of base's display(), since object copy of base of smartpc?

another question if add line temp->data; in convert() function , says pc::data protected accessing derived class scope i.e smartpc, why doesn't work?

any appreciated.

according scott meyers : static_cast<pc*>(this); create temp base copy of smartpc. temp->display(); executed display() function of derived class why so? should execute function of base's display() , since object copy of base of smartpc.

no copy created, casting a pointer.

since class polymorphic, calling virtual function via pointer results in calling "correct" version of function (according dynamic type of object, smartpc *).

if, instead, display not virtual, version of base class have been called, since nonvirtual methods it's static type of pointer determine version called.

(display virtual in smartpc if it's not explicitly specified, virtual qualifier implied when overriding inherited virtual functions)

---

notice instead if did:

pc temp(*this); 

you have created copy of current object, "sliced" object of type pc. called "object slicing" , performed copy constructor of pc; undesired behavior (because object of derived class becomes object of base class, , polymorphism not work may expect).

---

another question if add line temp->data; in convert() function , says pc::data protected accessing derived class scope i.e smartpc, why doesn't works?

conceptually, when try access temp->data you're trying access private member of object (it's not important temp this), access denied. "derived class privileges" access protected members work on this.