Polymorphism c++

Question

In some books there is written that class that declares or inherits a virtual function is called a polymorphic class.

Class B doesn't have any virtual functions but passes more than one is-a test.

Class C has one virtual function but doesn't inherit.

class A {};
class B : public A {};

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

is class B or C polymorphic ?

Answer 1

2003: 10.3/1 states, clearly:

A class that declares or inherits a virtual function is called a polymorphic class.

You actually said this yourself, word-for-word, so I don't really understand what the question is.

C (and its descendants, if you add any) is polymorphic; A and B are not.

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^{Note that, in a wider OOP sense, you can always perform some "polymorphism" in that C++ always allows you to upcast; thus all objects that inherit can be treated as a different (but related) type.}

^{However, the term "polymorphic" is defined slightly differently in C++, where it has more to do with whether you can downcast as well. If you don't want to be confusing like the C++ standard, you might call this "dynamic polymorphism".}