polymorphism - Virtual keyword use in C++ -

i understand c++ implements runtime polymorphism thorugh virtual functions , virtual keyword inherited don't see use of virtual keyword in derived class.

e.g. in below case if dropped virtual keyword in derived class still ptr->method() call goes derived::method. virtual keyword doing in derived class?

#include<iostream>  using namespace std;  class base { public:     virtual void method()     {         std::cout << std::endl << "base" << std::endl;     } };  class derived: public base { public:     virtual void method()     {         std::cout << std::endl << "derived" << std::endl;     } };  int main() {     base* ptr = new derived();     ptr->method();     return 9; } 

nothing. remind functions virtual or not.