Question

Complete the table on the next page by filling in private, protected, public, or inaccessible in the right-hand column: $$\begin{array}{ll} \hline \text { In a private base class, this base class } & \ldots \text { becomes this access specification in } \\ \text { MEMBER access specification... } & \text { the derived class. } \\ \hline \text { private } & & \\ \text { protected } & & \\ \text { public } & & \\ \hline \end{array}$$

Short answer

Answer: When a base class is inherited privately, all private members become inaccessible, protected members become private, and public members also become private.

Step-by-step solution

Understanding class inheritance and access specifiers

In C++, when a class is derived from another class (the base class), their member access specifiers (private, protected, and public) determine the accessibility of those members in the derived class. Whenever the type of inheritance is private, it affects the access specifiers in the derived class in a specific way.

Inheritance: Private

When a base class is inherited privately, all its access specifiers have their member access levels changed in the derived class as follows: 1. Private members become inaccessible. 2. Protected members become private. 3. Public members also become private. Now, let's use this information to complete the table.

Completing the table

Using our understanding of private inheritance, let's fill in the right-hand column of the table with the access specifications resulting from a private base class: $$\begin{array}{ll} \hline \text { In a private base class, this base class } & \ldots \text { becomes this access specification in } \\\ \text { MEMBER access specification... } & \text { the derived class. } \\\ \hline \text { private } & \text { inaccessible } \\\ \text { protected } & \text { private } \\\ \text { public } & \text { private } \\\ \hline \end{array}$$

Key concepts

Access Specifiers

In C++, access specifiers are used to define how the members (attributes and methods) of a class can be accessed. They include public, protected, and private:

• Public: Members declared as public can be accessed from anywhere in the program where the object is visible. This is the most permissive access level.
• Protected: Members marked as protected are accessible within the class itself and by any derived class. It offers a middle ground between private and public access levels.
• Private: Private members are accessible only within the class that defines them. They are not accessible directly outside the class nor by derived classes, unless through a member of the original class that has access to them.

Understanding these specifiers is crucial when designing class interfaces and when implementing inheritance, as they directly influence how a class can interact with other parts of the program. Think of access specifiers as the doors to a house, where only certain people have keys.

Private Inheritance

In private inheritance, a base class is inherited such that the accessibility of its members is altered in the derived class. This means that the derived class cannot access any of the base class's public or protected members directly.

• Private members: Completely inaccessible to the derived class; they cannot be accessed or used.
• Protected members: Become private in the derived class, restricting their accessibility to within the derived class only.
• Public members: Also become private in the derived class, meaning even those initially accessible from the outside in the base class are shielded in the derived version.

Private inheritance is akin to internally using the properties of the base class without exposing them for further inheritance. It effectively turns everything in the base class to an internal implementation detail for the derived class.

Class Hierarchy

The concept of class hierarchy in C++ refers to the structured relationship between a base class and derived classes. It's a fundamental part of object-oriented programming that reflects real-world hierarchies and allows for code reuse and organization. In C++, a class hierarchy is often visualized as a tree:

• Base Class: The root or trunk of the tree. It provides a template for its derived classes, containing common attributes and methods.
• Derived Class: The branches stemming from the base class. Each derived class can have its unique attributes and methods in addition to those inherited from the base class.
• Multi-Level Inheritance: Derived classes can themselves act as base classes for newer classes, creating deeper branches within the hierarchy.

Establishing an effective class hierarchy is essential for managing complex systems, enabling changes and updates in a single place without extensive modifications elsewhere in the code.

Member Accessibility

Member accessibility in C++ is a cornerstone for understanding how data and functions within objects can interact. It combines the use of access specifiers and inheritance to determine which members can be accessed and utilized. When examining member accessibility:

• Private Members: These members cannot be inherited or accessed by derived classes, except indirectly through public or protected methods within the class they belong to.
• Protected Members: These are accessible within their class and by derived classes, but in the context of private inheritance, they turn into private, limiting their visibility.
• Public Members: Normally accessible from outside the class, but private inheritance converts them into private members, constraining direct access from outside.

Understanding these mechanisms is vital for safely managing member functions and data, ensuring that the integrity and security of classes are maintained throughout their usage in different program modules.