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() ?
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.
It's better style to include the virtual keyword. But it's not required.
No difference.
Once foo is virtual, its virtual forever in the class-hierarchy, no matter how far you go from the base in the class-hierarchy.
But I prefer to write virtual even in overrridden functions, because it adds readability to the code, which matters a lot.
