c++ - Calling a virtual function on a reference -

in following code, why last call of eat() on reference c return "an animal b eating." ? understanding, c reference instance b of derived class dog , eat() virtual function. should have returned "a dog b eating."

#include <string> #include <iostream>  using namespace std;  class animal {  protected:     string name;  public:     animal( string _name ):     name(_name)     {      }      virtual void eat()     {          cout << "an animal " << name << " eating." << endl;     } };  class dog : public animal {  public:      dog( string _name ):     animal(_name)     {      }      void eat()     {         cout << "a dog " << name << " eating." << endl;     } };  int main( int argc , char ** argv ) {     animal a("a");     a.eat();      dog b("b");     b.eat();      animal & c = a;     c.eat();      c = b;     c.eat();      return 0; } 

this output:

an animal eating.  dog b eating.   animal eating.   animal b eating. 

in order make use of dynamic polymorphism provided virtual functions (distinguishing between derived , base classes during runtime), need access derived class object via base class pointer or reference.

i've commented out code confusion might have taken place:

int main( int argc , char ** argv ) {      animal a("a");     a.eat();      dog b("b");     b.eat();      // make reference (alias) animal object , set object a.      // point on, whenever write c, think "a".     animal & c = a;     // so, a.eat()     c.eat();      // = b (animal = dog): danger! slicing! here, assignment operator     // slices derived object , assigns base object "part" (remember,      // read "a", see "c" in code):      // a.operator=(const a& b)     c = b;     // a.eat() = object of type a, naturally, here call a::eat()     c.eat();      return 0; }