Those actually all return 4. Since f is virtual in the base class, it remains virtual in all derived classes, regardless of whether they say so explicitly. The

Those actually all return 4. Since f is virtual in the base class, it remains virtual in all derived classes, regardless of whether they say so explicitly. The override keyword was added in C++11 to help prevent the sort of mistake you were trying to show. Any methods you mark with it will result in a compile error if they are not actually overriding anything. For example, if B::g were marked as override, it would fail to compile because A::g is not virtual.