statquant statquant - 1 month ago 6x
C++ Question

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

I have an pure virtual base class and a derived class. I know I am allowed to implement a virtual (not pure) method in the base class.
What I do not understand is why I

to also implement the same method in the derived class if what I want is simply to use the base implementation:

#include <iostream>

using namespace std;

class Abstract {
int x;
cout << "Abstract constructor" << endl;
x = 1;
virtual void foo() = 0;
virtual void bar(){
cout << "Abstract::bar" << endl;

class Derived : Abstract {
int y;
Derived(int _y):Abstract(){
cout << "Derived constructor" << endl;
virtual void foo(){
cout << "Derived::foo" << endl;
virtual void bar(){

int main()
cout << "Hello World" << endl;
Derived derived(2);;; //HERE I HAVE TO DEFINE Derived::bar to use it
return 0;


You don’t have to do that. You can do the following:

class Derived : public Abstract {

That way, you can use the public methods from the base class.