Top 30 Most Common C++ Oops Interview Questions You Should Prepare For
Written by
James Miller, Career Coach
Preparing for a C++ interview, especially one focusing on Object-Oriented Programming (OOP), requires a solid understanding of core concepts. C++ is a powerful language widely used in systems programming, game development, high-frequency trading, and performance-critical applications. Mastery of its OOP principles is not just about syntax; it's about understanding how to design robust, maintainable, and scalable software. Interviewers often probe candidates' knowledge of classes, objects, encapsulation, inheritance, polymorphism, and abstraction to assess their ability to build well-structured C++ applications. These concepts are fundamental to writing idiomatic C++ code that leverages the language's strengths. Acing your c++ oops interview questions demonstrates proficiency in one of the most critical aspects of C++ development, setting you apart as a capable candidate. This article provides a curated list of 30 common c++ oops interview questions to help you structure your study and build confidence.
What Are c++ oops interview questions?
C++ OOP interview questions are designed to evaluate a candidate's comprehension of the fundamental principles of Object-Oriented Programming as they apply to C++. These questions cover topics such as the definition of a class and an object, the purpose and implementation of the four pillars of OOP: encapsulation, inheritance, polymorphism, and abstraction, as well as related concepts like constructors, destructors, virtual functions, access specifiers, operator overloading, and memory management techniques like RAII and smart pointers. Interviewers use these questions to gauge how well candidates can translate theoretical OOP knowledge into practical C++ code design. A strong grasp of these concepts is essential for writing clean, modular, and efficient C++ programs. Preparing specifically for these types of c++ oops interview questions will give you a significant advantage in your technical interviews.
Why Do Interviewers Ask c++ oops interview questions?
Interviewers ask c++ oops interview questions for several key reasons. Firstly, they want to confirm that candidates have a foundational understanding of how C++ is typically used to build complex systems. OOP principles are central to designing large-scale C++ applications. Secondly, these questions help assess a candidate's problem-solving approach and their ability to structure code logically and efficiently. Understanding concepts like polymorphism and inheritance is crucial for writing reusable and flexible code. Thirdly, questions about memory management (like RAII, smart pointers) are vital in C++, as manual memory handling can be error-prone. Demonstrating knowledge in these areas shows responsible coding practices. Finally, discussing OOP allows interviewers to evaluate how candidates think about software design patterns and architectural choices, which is critical for collaborative development environments. Excelling at c++ oops interview questions indicates a candidate is ready to tackle challenging C++ projects.
Preview List
What is Object-Oriented Programming (OOP) in C++?
Why do we need OOP?
What is a class and an object?
What is encapsulation?
What is inheritance?
What are the different types of inheritance in C++?
What is polymorphism?
What is abstraction?
What is a constructor?
What are the types of constructors in C++?
What is a destructor?
What is operator overloading?
What are access specifiers in C++?
What is function overloading?
What is function overriding?
What is the difference between class and struct in C++?
What is a virtual function?
What is a pure virtual function and abstract class?
What is multiple inheritance? What problem does it cause?
What is the diamond problem and its solution?
What is a copy constructor?
What is the difference between shallow copy and deep copy?
What are static members and static member functions?
What is friend function?
What is RAII (Resource Acquisition Is Initialization)?
What are smart pointers and how do they relate to OOP?
What is the difference between call by value and call by reference?
What is the scope resolution operator (::)?
How do you prevent copying of objects in C++?
What is a singleton class and how is it implemented?
1. What is Object-Oriented Programming (OOP) in C++?
Why you might get asked this:
This is a fundamental question to check if you know the basic definition and purpose of OOP, setting the stage for more detailed questions.
How to answer:
Define OOP and list the four main pillars (encapsulation, inheritance, polymorphism, abstraction). Briefly mention its goals like modularity and reusability.
Example answer:
OOP is a programming paradigm using objects and classes to structure code. It bundles data and methods, emphasizing principles like encapsulation, inheritance, polymorphism, and abstraction to create modular, reusable, and maintainable software.
2. Why do we need OOP?
Why you might get asked this:
Interviewers want to know if you understand the benefits and practical advantages OOP brings over procedural programming for complex projects.
How to answer:
Explain how OOP helps manage complexity, promotes code reuse, improves maintainability, and enhances security through data hiding.
Example answer:
OOP provides a clear structure for programs, making them easier to understand and maintain. It promotes code reuse through inheritance, reduces redundancy, hides data via encapsulation, and increases flexibility using polymorphism, aiding in large-scale development.
3. What is a class and an object?
Why you might get asked this:
These are the most basic building blocks of OOP. Knowing the difference confirms your understanding of the core concepts.
How to answer:
Define a class as a blueprint or template. Define an object as an instance of a class, occupying memory and having state and behavior.
Example answer:
A class is a blueprint or template defining data (members) and methods (functions). An object is a real-world instance of a class, created in memory based on the class definition, possessing specific data values and behaviors.
4. What is encapsulation?
Why you might get asked this:
Tests your understanding of data hiding and bundling data with methods, a key principle for data integrity and modularity.
How to answer:
Describe it as wrapping data and methods into a single unit (a class). Explain how access specifiers restrict direct access, protecting data.
Example answer:
Encapsulation is bundling data members and member functions within a class. It involves restricting direct access to data using access specifiers like private, controlling how data is modified, which protects data integrity and simplifies the interface.
5. What is inheritance?
Why you might get asked this:
Evaluates your knowledge of code reuse and establishing relationships between classes, fundamental for building class hierarchies.
How to answer:
Define it as a mechanism where one class (derived/child) acquires properties and behaviors from another (base/parent). Explain its purpose: code reuse.
Example answer:
Inheritance allows a new class (derived class) to inherit attributes and behaviors from an existing class (base class). This promotes code reuse, saving time and effort by not having to rewrite common functionalities, and models 'is-a' relationships.
6. What are the different types of inheritance in C++?
Why you might get asked this:
Checks your detailed knowledge of C++'s specific inheritance models, including potential complexities like multiple inheritance.
How to answer:
List and briefly describe the common types: Single, Multiple, Multilevel, Hierarchical, and Hybrid.
Example answer:
C++ supports several types: Single (one base, one derived), Multiple (multiple bases, one derived), Multilevel (chain of inheritance), Hierarchical (one base, multiple derived), and Hybrid (a combination of two or more types).
7. What is polymorphism?
Why you might get asked this:
A crucial OOP concept. This question assesses your understanding of how one interface can have multiple forms, enabling flexibility.
How to answer:
Define polymorphism ("many forms"). Explain the two main types in C++: compile-time (function overloading) and runtime (function overriding using virtual functions).
Example answer:
Polymorphism means "many forms," allowing a single interface to represent different underlying forms (types). In C++, it occurs via function overloading (compile-time) and function overriding using virtual functions (runtime), enabling flexible and dynamic behavior.
8. What is abstraction?
Why you might get asked this:
Tests your understanding of hiding complexity and showing only essential features, important for managing large systems.
How to answer:
Describe it as hiding implementation details and exposing only necessary features. Mention abstract classes and pure virtual functions as C++ mechanisms for abstraction.
Example answer:
Abstraction involves hiding complex implementation details and showing only the essential features of an object. It focuses on "what" an object does rather than "how." In C++, this is often achieved through abstract classes and pure virtual functions.
9. What is a constructor?
Why you might get asked this:
Fundamental knowledge of object initialization is key. Constructors are essential for setting up objects correctly.
How to answer:
Define it as a special member function called automatically upon object creation. Explain its purpose: initializing object data members. Mention its characteristics (same name as class, no return type).
Example answer:
A constructor is a special member function that runs automatically when an object is created. Its primary role is to initialize the object's data members. It shares the class name and does not have any return type, not even void.
10. What are the types of constructors in C++?
Why you might get asked this:
Evaluates deeper knowledge of object creation scenarios, including initialization from other objects.
How to answer:
List and briefly explain the common types: Default, Parameterized, Copy, and (since C++11) Move constructors.
Example answer:
C++ has Default (no parameters), Parameterized (takes arguments for initialization), Copy (initializes an object from another object of the same class), and Move (efficiently transfers resources from a temporary object, C++11+) constructors.
11. What is a destructor?
Why you might get asked this:
Tests understanding of object cleanup and resource management, critical in C++ to prevent memory leaks.
How to answer:
Define it as a special member function called when an object's lifetime ends. Explain its purpose: releasing resources acquired by the object. Mention its characteristics (same name as class prefixed by ~, no return type, no parameters).
Example answer:
A destructor is a special member function invoked automatically when an object goes out of scope or is explicitly deleted. Its purpose is to clean up resources, such as dynamic memory or file handles, used by the object during its lifetime.
12. What is operator overloading?
Why you might get asked this:
Checks your understanding of how to extend C++'s operators to work with user-defined types, improving code readability for custom objects.
How to answer:
Explain that it allows redefining the behavior of operators for class objects. Give a simple example like '+' for object addition.
Example answer:
Operator overloading lets you redefine how standard C++ operators (like +, -, *, ==, etc.) work when applied to objects of your custom classes. This provides a more intuitive syntax for operations involving objects, like adding two complex numbers.
13. What are access specifiers in C++?
Why you might get asked this:
Fundamental to encapsulation and controlling visibility of class members. This is a basic OOP concept check.
How to answer:
List the three specifiers: public, private, and protected. Explain the scope of access for members under each specifier.
Example answer:
Access specifiers (public, private, protected) control the visibility and accessibility of class members. Public members are accessible from anywhere. Private members are only accessible within the class. Protected members are accessible within the class and by derived classes.
14. What is function overloading?
Why you might get asked this:
Tests knowledge of compile-time polymorphism, a common technique for providing functions with similar names but different parameters.
How to answer:
Define it as having multiple functions with the same name in the same scope but different parameter lists (different number, type, or order of arguments). State that the compiler resolves the call at compile-time.
Example answer:
Function overloading allows defining multiple functions with the same name in the same scope, provided they have different parameter lists (signatures). The compiler determines which function to call based on the arguments supplied at compile-time.
15. What is function overriding?
Why you might get asked this:
Evaluates understanding of runtime polymorphism, essential for working with inheritance hierarchies and virtual functions.
How to answer:
Explain it as a derived class providing a specific implementation for a function already defined in its base class. Mention that the base class function must be virtual for runtime overriding.
Example answer:
Function overriding occurs when a derived class implements a function with the exact same signature as a function declared in its base class. If the base function is virtual, the derived class version is called through a base class pointer/reference at runtime.
16. What is the difference between class and struct in C++?
Why you might get asked this:
A classic C++ specific question that highlights subtle differences and historical context.
How to answer:
The key difference is the default access specifier: private for classes, public for structs. Note that otherwise, they are very similar and structs can have member functions, constructors, etc.
Example answer:
In C++, the primary difference is the default access specifier for members: 'private' for class and 'public' for struct. Functionally, both can contain data members, member functions, constructors, destructors, etc.
17. What is a virtual function?
Why you might get asked this:
Central to runtime polymorphism. This question assesses your understanding of how dynamic dispatch works in C++.
How to answer:
Define it as a member function in a base class declared with the virtual keyword. Explain that it allows for dynamic dispatch (runtime polymorphism), where the actual function called is determined by the object type pointed to, not the pointer type.
Example answer:
A virtual function is a member function declared using the virtual keyword in a base class. It enables runtime polymorphism, meaning the specific function executed is determined by the actual type of the object being pointed to or referenced, rather than the type of the pointer or reference.
18. What is a pure virtual function and abstract class?
Why you might get asked this:
Tests your knowledge of abstraction mechanisms in C++, specifically how to create interfaces and enforce derived class implementations.
How to answer:
Define a pure virtual function (declared with = 0) as one that has no implementation in the base class, forcing derived classes to provide one. Define an abstract class as any class containing at least one pure virtual function, noting that it cannot be instantiated.
Example answer:
A pure virtual function is declared in a base class by = 0 (e.g., virtual void draw() = 0;), indicating no implementation in the base class. A class with at least one pure virtual function is an abstract class and cannot be instantiated directly; it serves as an interface or base for other classes.
19. What is multiple inheritance? What problem does it cause?
Why you might get asked this:
Checks understanding of a more complex inheritance type and its associated issues.
How to answer:
Define multiple inheritance (inheriting from more than one base class). Explain that the main problem is the "diamond problem."
Example answer:
Multiple inheritance is when a class inherits from more than one base class. A common issue is the "diamond problem," which occurs when a class inherits from two classes that share a common grandparent, leading to ambiguity regarding the grandparent's members.
20. What is the diamond problem and its solution?
Why you might get asked this:
Specific follow-up to multiple inheritance, assessing your ability to identify and resolve complex inheritance ambiguities.
How to answer:
Describe the diamond problem scenario. Explain that the solution in C++ is virtual inheritance, which ensures only one shared subobject of the common base class exists in the derived class.
Example answer:
The diamond problem arises in multiple inheritance when a class inherits from two classes, both of which inherit from a common base. This creates a 'diamond' shape in the hierarchy and ambiguity. C++ resolves this using virtual inheritance for the common base class.
21. What is a copy constructor?
Why you might get asked this:
Fundamental question about object initialization, especially when objects are passed by value or returned from functions.
How to answer:
Define it as a constructor used to initialize an object using another existing object of the same class. Mention when it is implicitly called (passing/returning by value, explicit creation).
Example answer:
A copy constructor is a special constructor that initializes a new object as a copy of an existing object of the same class. It is automatically called when an object is passed by value, returned by value, or explicitly constructed as a copy.
22. What is the difference between shallow copy and deep copy?
Why you might get asked this:
Critical for understanding how constructors and assignment operators should handle dynamically allocated memory within objects to avoid issues like double deletion.
How to answer:
Explain shallow copy copies member values directly (pointers copy the address). Explain deep copy creates new resources for pointed-to data, ensuring independent copies. State when deep copy is needed (when class manages dynamic memory).
Example answer:
Shallow copy copies member values directly. If a member is a pointer, only the pointer value (memory address) is copied, making both objects point to the same resource. Deep copy allocates new memory for pointed-to data and copies the contents, ensuring independent resource ownership.
23. What are static members and static member functions?
Why you might get asked this:
Tests understanding of members that belong to the class itself rather than individual instances, useful for class-level data or utility functions.
How to answer:
Explain that static members belong to the class, shared by all objects. Static member functions can only access static members and are called using the class name.
Example answer:
Static members (data or functions) belong to the class itself, not to any specific object. There's only one copy shared among all objects. Static functions can only access static members and are invoked using the class name (e.g., ClassName::staticFunction()).
24. What is friend function?
Why you might get asked this:
Assesses knowledge of controlled relaxation of encapsulation, used when a non-member function needs access to private/protected data.
How to answer:
Define it as a non-member function (or another class's member function) declared inside a class with the friend keyword, granting it access to the class's private and protected members.
Example answer:
A friend function is a non-member function or a function of another class that is declared as a 'friend' inside a class. This declaration grants the friend function special permission to access the private and protected members of that class.
25. What is RAII (Resource Acquisition Is Initialization)?
Why you might get asked this:
A fundamental C++ idiom for safe resource management (memory, files, locks). Demonstrates good C++ practice.
How to answer:
Explain that it's a technique where resource acquisition is done in an object's constructor, and resource release in its destructor. This ties resource lifetime to object lifetime, guaranteeing cleanup even during exceptions.
Example answer:
RAII is a C++ programming idiom where resource acquisition (like memory allocation or opening a file) happens in an object's constructor, and resource release occurs in its destructor. This ensures resources are correctly managed and cleaned up automatically when the object goes out of scope.
26. What are smart pointers and how do they relate to OOP?
Why you might get asked this:
Modern C++ practice for robust memory management. Tests knowledge of tools that support RAII and prevent common pointer-related bugs.
How to answer:
Define smart pointers (e.g., uniqueptr, sharedptr) as objects that manage dynamic memory. Explain they automate resource release via RAII, improving memory safety and exception handling. Relate them to OOP by showing how they encapsulate raw pointers and their management.
Example answer:
Smart pointers like uniqueptr and sharedptr are objects that manage dynamic memory. They use RAII to automatically deallocate memory when they go out of scope. They relate to OOP by encapsulating raw pointers and their lifecycle, enhancing resource safety and simplifying memory management.
27. What is the difference between call by value and call by reference?
Why you might get asked this:
A fundamental programming concept, but crucial in C++ due to pointers and references affecting efficiency and mutability.
How to answer:
Explain call by value passes a copy of the argument, so modifications inside the function don't affect the original. Explain call by reference (using pointers or references) passes a link to the original data, allowing modifications.
Example answer:
Call by value passes a copy of the argument; changes inside the function don't affect the original variable. Call by reference, using references (&) or pointers (*), passes a direct or indirect link to the original variable, allowing the function to modify the original data.
28. What is the scope resolution operator (::)?
Why you might get asked this:
Tests knowledge of how to access members outside a class definition or handle name conflicts.
How to answer:
Explain its primary uses: defining a member function outside its class, and accessing a static member. Also, mention its use for accessing a global variable when a local variable has the same name.
Example answer:
The scope resolution operator (::) is used primarily to define a member function outside its class definition, or to access a class's static members. It can also be used to access a global variable when a local variable with the same name exists.
29. How do you prevent copying of objects in C++?
Why you might get asked this:
Relevant for classes managing unique resources (like unique_ptr) or when copying makes no logical sense. Tests understanding of copy control.
How to answer:
Explain that the copy constructor and copy assignment operator need to be disabled. In C++11+, this is best done using = delete. Before C++11, you would declare them private and not define them.
Example answer:
To prevent object copying, you should disable the copy constructor and the copy assignment operator. In modern C++ (C++11 and later), the standard way is to declare them within the class definition and mark them = delete.
30. What is a singleton class and how is it implemented?
Why you might get asked this:
Tests knowledge of a common design pattern often implemented using OOP principles (private constructor, static method).
How to answer:
Define a singleton as a class that allows only one instance of itself. Explain implementation usually involves a private constructor, a static member pointer to the instance, and a public static method to get the instance, ensuring lazy or eager initialization.
Example answer:
A singleton class is designed to have only one instance throughout the application's lifetime. Implementation typically involves making the constructor private, using a static member variable to hold the single instance, and providing a public static method to access that instance, often creating it upon the first request.
Other Tips to Prepare for a c++ oops interview questions
Beyond memorizing answers to common c++ oops interview questions, effective preparation involves practicing coding, understanding underlying concepts deeply, and simulating the interview environment. As the famous quote goes, "Theory without practice is barren; practice without theory is blind." Applying OOP principles in small coding exercises will solidify your understanding far better than just reading definitions. Consider working through problems on platforms like LeetCode or HackerRank, specifically focusing on problems that can be solved using classes and objects. Practice explaining your thought process out loud. Tools like Verve AI Interview Copilot can be invaluable here, offering realistic mock interviews and personalized feedback to help you refine your answers to c++ oops interview questions and improve your technical communication skills. Verve AI Interview Copilot provides a safe space to practice, helping you become more comfortable articulating complex C++ concepts under pressure. Utilizing resources like Verve AI Interview Copilot (https://vervecopilot.com) for mock interviews can significantly boost your confidence before facing real c++ oops interview questions. Remember, preparation is key, and using tools like Verve AI Interview Copilot can make your study time more effective.
Frequently Asked Questions
Q1: How long should my answers to c++ oops interview questions be?
A1: Aim for concise, clear answers directly addressing the question, usually 1-3 sentences for definitions, with brief examples if requested.
Q2: Should I provide code examples for c++ oops interview questions?
A2: Yes, be prepared to write small code snippets on a whiteboard or shared editor to illustrate concepts like inheritance or polymorphism.
Q3: Are there common follow-up questions to basic c++ oops interview questions?
A3: Yes, interviewers often ask about practical scenarios, potential issues (like the diamond problem), or differences between related concepts.
Q4: How important is memory management knowledge in c++ oops interview questions?
A4: Extremely important. C++'s explicit memory handling makes RAII, smart pointers, and understanding copy semantics crucial topics.
Q5: Should I mention modern C++ features in c++ oops interview questions?
A5: Absolutely. Discussing features like = delete or uniqueptr/sharedptr shows you are up-to-date with best practices.
Q6: How can I practice answering c++ oops interview questions effectively?
A6: Practice explaining concepts out loud, whiteboard coding, and use mock interview platforms like Verve AI Interview Copilot to simulate the experience.
