c++ - Why does this virtual method return true? -

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while taking tutorial on polymorphism in c++, code seems acting strangely on call non-overriden virtual method. here classes:

// classes.cpp  namespace classes {     class c     {     public:         virtual bool has_eyesight()         {             return false;         }     } c;      class see : public c     {     public:         bool has_eyesight() override         {             return true;         }     } si; }

and here main method:

// file.cpp  #include <iostream> #include "classes.cpp"  using std::cout; using std::endl; using classes::c; using classes::see;  int main() {     see& si = classes::si;      cout << si.has_eyesight() << endl;      c& c = si;      cout << c.has_eyesight() << endl;      c = classes::c;      cout << c.has_eyesight() << endl; }

this code print 1 1 1 (true true true) when run; shouldn't c.has_eyesight() return false if references c , not see?

(forgive me if sounds naive, started learning c++.)

let's go through you're doing here.

c& c = si;

c reference classes::si, instance of see. vtable points of see, , has_eyesight() return true.

the main difference between reference , pointer can't modify target - c point classes::si, no matter do. meaning...

c = classes::c;

this not change reference classes::c. cannot modify reference. instead, calls assignment operator on c, you're copying classes::c on classes::si. unless overload operator=, member-by-member copy. not modify vtable, has_eyesight() continue return true.

if want make point else, have use pointer:

see* si = &classes::si; cout << si->has_eyesight() << endl; c* c = si; cout << c->has_eyesight() << endl; c = &classes::c; cout << c->has_eyesight() << endl;

try this.


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