Deriving a class may be forbidden with final specifier. Let’s declare a final class:

class A final {
};

Now any attempt to subclass it will cause a compilation error:

// Compilation error: cannot derive from final class:
class B : public A {
};

Final class may appear anywhere in class hierarchy:

class A {
};

// OK.
class B final : public A {
};

// Compilation error: cannot derive from final class B.
class C : public B {
};