virtual qualifier in derived class

Question

Does the virtual qualifier to a virtual function of base class, in the derived class makes any difference ?

class b
{
   public:
   virtual void foo(){}
};

class d : public b
{
  public:
  void foo(){ .... }
};

or

class d : public b
{
  public:
  virtual void foo(){ .... }
}; 

Is there any difference in these two declarations, apart from that it makes child of d make aware of virtuality of foo() ?

Answer 1

It makes no difference. foo is virtual in all classes that derive from b (and their descendants).

From C++03 standard, §10.3.2:

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 and same parameter list as Base::vf is declared, then Derived::vf is also virtual (whether or not it is so declared) and it overrides Base::vf.