Question

Assume the declaration of Exercise \(12 .\) Suppose that class third is derived from class first using the statement: class third: protected first Determine which members of class first are private, protected, and public in class third.

Short answer

Private members stay private and are thus inaccessible, protected members remain protected, and public members become protected in class 'third'.

Step-by-step solution

Understanding the Class Declaration

In the given exercise, class 'third' is derived from class 'first' using the keyword 'protected'. This means that the access specifier for members inherited from class 'first' can change when they become part of class 'third'. To determine the access level of class members, we need to consider how the 'protected' inheritance affects each type of member in 'first'.

Analyzing Private Members

In C++, private members of a base class are not accessible directly by derived classes, regardless of the type of inheritance used (public, protected, or private). Therefore, private members of class 'first' remain private and inaccessible in class 'third'.

Analyzing Protected Members

Protected members of the base class 'first' maintain their protected status in the derived class 'third' when using protected inheritance. This means that protected members are accessible within class 'third' and by any classes further derived from 'third'.

Analyzing Public Members

Public members of the base class 'first' become protected in the derived class 'third' when protected inheritance is used. Therefore, although these members are public in 'first', they are now only accessible within 'third' and its derived classes as protected members.

Key concepts

Access Specifiers

In C++, access specifiers determine how the members (variables and functions) of a class can be accessed. There are three main types of access specifiers:

• Private: Members declared as private are only accessible within the class itself. They cannot be accessed directly by derived classes or outside any class methods. This ensures encapsulation and data hiding.
• Protected: Members labeled as protected are accessible within the class and by any derived classes. This provides more flexibility compared to private access, especially in situations involving class hierarchies and inheritance.
• Public: Members declared as public can be accessed from any part of the program. Public access is the most open form of access and should be used only when necessary.

Understanding these access levels is crucial for managing data safety and effective code structuring in C++ programs.

Protected Inheritance

When a class inherits from another class using protected inheritance, it affects the accessibility of the base class members in the derived class. Protected inheritance allows deriving some flexibility while maintaining control over access levels.

• Private members: These remain inaccessible from derived classes even with protected inheritance, as private access restricts access strictly to the class itself.
• Protected members: These retain their protected status in the derived class, making them accessible only within the derived class and any further derived classes.
• Public members: These become protected in the derived class. Applying protected inheritance means that originally public members from the base class become more restricted in their access.

This mechanism is particularly useful when you want to prevent classes from freely accessing all data from a base class while still utilizing the benefits of inheritance.

Base Class Members

A base class in C++ defines members which are inherited by other classes. Understanding the impact of inheritance on the visibility and accessibility of these members is key to implementing effective object-oriented programming.

• Private Members: These are not directly accessible or inherited by derived classes and are usually accessed through public or protected methods.
• Protected Members: These can be accessed in derived classes, providing a way to share implementation details while keeping strict control over who can modify class internals.
• Public Members: These are accessible from anywhere once the base class is instantiated, offering direct interaction with the base class API.

Understanding how each member type behaves when inherited helps in designing class hierarchies that are robust and maintainable.

Derived Class

In object-oriented programming, a derived class is a class that inherits members and behaviors from another class, known as the base class.

• Inheritance: The derived class gains access to some or all members of the base class depending on the inheritance specifier (public, protected, or private) used.
• Modification and Extension: Derived classes can add new functions or override existing ones from the base class, providing a mechanism for extension and customization.
• Access Control: When a class is inherited, the access level to the base class members is determined by the type of inheritance along with the original access specifiers in the base class.

Derived classes enable reusability and a hierarchical structuring of code, allowing programmers to build complex systems from simpler, well-defined components.