Navigating C++ and Object-Oriented Design

11.5. Protected Access

Somewhere between night and day is twilight, which has properties of both. This analogy helps explain protected in class definitions, which has access rules between private and public. In a base class, protected acts like private for users and public for derived classes. Protected, therefore, relates only to inheritance hierarchies.

Protected grants access to a subset of an object's attributes and operations for derived classes of any depth. Protected is important in class design hierarchies because a subsequently derived class may call member functions or read and write data members that are inappropriate for users to access. The designer of a base class can also provide specialized operations in a protected section that ...