C++ “virtual” keyword for functions in derived classes. Is it necessary?

Question

With the struct definition given below...

struct A {
    virtual void hello() = 0;
};

Approach #1:

struct B : public A {
           


        

Answer 1

The virtual keyword is not necessary in the derived class. Here's the supporting documentation, from the C++ Draft Standard (N3337) (emphasis mine):

10.3 Virtual functions

2 If a virtual member function vf is declared in a class Base and in a class Derived, derived directly or indirectly from Base, a member function vf with the same name, parameter-type-list (8.3.5), cv-qualification, and ref-qualifier (or absence of same) as Base::vf is declared, then Derived::vf is also virtual (whether or not it is so declared) and it overrides Base::vf.