Question

I know that when you want to declare a polymorphic function you have to declare the base class function virtual.

class Base
{
public:
    virtual void f();
};

My question is are you required to declare the inheriting class function as virtual, even if it’s expected that Child behaves as if it were “sealed”?

class Child : public Base
{
public:
    void f();
};

Answer 1

No, you don’t need to re-declare the function virtual.

A virtual function in a base class will automatically declare all overriding functions as virtual:

struct A
{
   void foo();          //not virtual
};
struct B : A
{
   virtual void foo();  //virtual
}
struct C : B
{
   void foo();          //virtual
}