In C++ inheritance, which of the following can a derived class inherit from its base class (subject to access control)?

Introduction / Context:
Inheritance is a fundamental concept in object oriented programming and is heavily used in C++. It allows a derived class to reuse and extend the behaviour and state of a base class. Understanding exactly what elements of a base class are inherited is crucial for designing class hierarchies correctly. This question asks you to identify whether a derived class inherits data, functions, or both from its base class.

Given Data / Assumptions:

• The language is C++.
• We are discussing single or multiple inheritance from a base class to a derived class.
• Access specifiers such as public, protected, and private control visibility but do not change the basic rule of what is inherited.
• Static members and friend relationships obey specific rules but follow the same inheritance visibility patterns.

Concept / Approach:
In C++, a derived class inherits both the data members and the member functions of its base class, subject to access controls. Public and protected members are inherited and accessible according to the inheritance mode and access rules, while private members are inherited but not directly accessible in the derived class. Member functions, including virtual functions, are also inherited and can be overridden where appropriate. This allows a derived class to reuse state and behaviour without reimplementing everything from scratch.

Step-by-Step Solution:
Step 1: Consider a base class with data members, such as int x, and member functions, such as void display(). Step 2: Define a derived class that publicly inherits from the base class. Step 3: Observe that the derived class objects contain the base class data members as part of their layout, even if some members are private and cannot be accessed directly. Step 4: Note that the derived class can call inherited public and protected member functions and can override virtual functions to extend behaviour. Step 5: From this, conclude that inheritance covers both data members and member functions, not just one or the other.

Verification / Alternative check:
You can verify this by creating a simple base class with a protected data member and a public function that uses it. Then derive a class and add a method that calls the base class function or directly uses the protected member. The derived class has access to both and can manipulate the inherited state and behaviour. Additionally, tools that display object layout will show that the derived class instance includes memory for base class data fields, confirming that data members are indeed inherited physically.

Why Other Options Are Wrong:
Option Data members only: This ignores the fact that member functions, including virtual functions, are also inherited and available to the derived class. Option Member functions only: This incorrectly suggests that the state represented by data members is not inherited, which is not true in C++. Option None of the above: This is incorrect because C++ inheritance explicitly covers both data members and functions, according to access rules.

Common Pitfalls:
A common confusion is about private members of the base class. They are inherited but cannot be accessed directly in the derived class; instead, they are accessible through public or protected member functions of the base class. Another pitfall is to assume that inheritance copies code in a textual sense, whereas it is actually a relationship defined in the type system and object layout. Keeping in mind that both data and behaviour are inherited helps in designing coherent and reusable class hierarchies.

Final Answer:
A derived class in C++ inherits Both data members and member functions from its base class, subject to access control rules.