c++ - Why do I have to implement a virtual function in a derived class if I want to use the base class implementation -

i have pure virtual base class , derived class. know allowed implement virtual (not pure) method in base class. not understand why have implement same method in derived class if want use base implementation:

#include <iostream>  using namespace std;  class abstract { public:     int x;     abstract(){         cout << "abstract constructor" << endl;         x = 1;     }     virtual void foo() = 0;     virtual void bar(){         cout << "abstract::bar" << endl;     } };  class derived : abstract { public:     int y;     derived(int _y):abstract(){         cout << "derived constructor" << endl;     }     virtual void foo(){         cout << "derived::foo" << endl;     }     virtual void bar(){         abstract::bar();     } };  int main() {    cout << "hello world" << endl;    derived derived(2);    derived.foo();    derived.bar(); //here have define derived::bar use    return 0; } 

you don’t have that. can following:

class derived : public abstract { 

that way, can use public methods base class.