C++ OOP Concepts Interview Questions
C++ Objects, Classes, Abstraction & Encapsulation
Basic Level (15 Questions)
What is Object-Oriented Programming (OOP) in C++?
Object-Oriented Programming is a programming paradigm that uses objects and classes to organize code. The four main principles of OOP are: Abstraction, Encapsulation, Inheritance, and Polymorphism.
What is a class in C++?
A class is a user-defined data type that serves as a blueprint for creating objects. It defines attributes (data members) and methods (member functions) that characterize objects of that type.
What is an object in C++?
An object is an instance of a class. It's a concrete entity created from a class blueprint that occupies memory. Objects have state (data members) and behavior (member functions).
What is abstraction in C++?
Abstraction is the process of hiding complex implementation details and showing only essential features. In C++, it's achieved using abstract classes, interfaces, and access specifiers.
What is encapsulation in C++?
Encapsulation is the bundling of data and methods that operate on that data within a single unit (class), while restricting direct access to some components. It's implemented using private and protected access specifiers with public getter/setter methods.
What are access specifiers in C++ classes?
C++ has three access specifiers: public (accessible from anywhere), private (accessible only within the class), and protected (accessible within the class and derived classes).
What is the difference between a class and a structure in C++?
In C++, the only difference is default access: class members are private by default, while struct members are public by default. Both can have constructors, methods, inheritance, etc.
What is a constructor in C++?
A constructor is a special member function that initializes objects of a class. It has the same name as the class and no return type. Types include: default, parameterized, copy, and move constructors.
What is a destructor in C++?
A destructor is a special member function that cleans up when an object is destroyed. It has the same name as the class preceded by a tilde (~). Called automatically when object goes out of scope or is deleted.
What is the 'this' pointer in C++?
The this pointer is an implicit pointer available in non-static member functions, pointing to the object for which the member function was called. Used to access members, return reference to current object, or resolve name conflicts.
What are static members in a C++ class?
Static data members are shared by all objects of the class (only one copy exists). Static member functions can be called without an object and can only access static members.
What are constant members and constant objects in C++?
const member functions cannot modify object data members. const objects cannot be modified after initialization and can only call const member functions.
What is an abstract class in C++?
An abstract class is a class that cannot be instantiated and serves as a base for other classes. It contains at least one pure virtual function (declared with = 0).
What are friend functions and friend classes in C++?
friend functions are non-member functions that have access to private and protected members of a class. friend classes have all their member functions as friends of another class.
What is the difference between encapsulation and abstraction?
Encapsulation is about hiding data and implementation details (how it works). Abstraction is about hiding complexity and showing only essentials (what it does). Encapsulation implements abstraction.
Tricky Level (10 Questions)
What are getter and setter methods in C++?
Getter methods (accessors) return the value of private data members. Setter methods (mutators) set/update the value of private data members. They provide controlled access to encapsulated data.
What is a copy constructor in C++?
A copy constructor creates a new object as a copy of an existing object. It takes a reference to an object of the same class as parameter. Example: ClassName(const ClassName &obj).
What is the Rule of Three in C++?
If a class requires a user-defined destructor, copy constructor, or copy assignment operator, it likely needs all three. This ensures proper resource management for classes that handle dynamic memory.
What are inline functions in C++ classes?
Inline functions are member functions defined inside the class (implicitly inline) or declared with the inline keyword. The compiler attempts to insert the function code directly at the call point to reduce function call overhead.
What is an object's lifetime in C++?
An object's lifetime begins when its constructor completes and ends when its destructor starts. Local objects are destroyed when they go out of scope, dynamic objects when deleted, and static/global objects at program termination.
What is the Rule of Five?
If you define destructor, copy constructor, copy assignment, move constructor, or move assignment, consider defining all five for resource-owning classes.
Difference between struct and class in C++?
Only default member access: public for struct, private for class. Otherwise identical.
What is a friend function?
Non-member granted access to private/protected members—useful for operators like operator<<.
What does `explicit` on constructors prevent?
Implicit conversions from single-argument constructors—reduces accidental conversions.
What is an aggregate in C++?
Array or class with no private/protected non-static data, no user constructors—supports brace initialization with special rules.
Note: These questions cover fundamental OOP concepts in C++ including objects, classes, abstraction, and encapsulation. Understanding these principles is crucial for object-oriented design and programming in C++. This page lists 15 basic and 10 tricky questions—use the tutorial and MCQ links above and below.