I still remember my first C++ developer interview—fresh out of college, confident, and completely blindsided by the depth of the questions. I walked in thinking I knew enough because I’d been coding for years. But when the interviewer started digging into memory management and object-oriented programming, I quickly realized there was much more to learn. Concepts like polymorphism and virtual functions tripped me up, and I wished I had prepared more thoroughly.
That experience taught me two critical lessons. First, C++ demands a deep understanding and can’t be approached casually. Second, thorough interview preparation is essential, especially with a language as complex and powerful as C++.
What interviewers love to test
From my interview experiences, I’ve learned that preparing for a C++ interview means diving deeper than just basic syntax. Interviewers often focus on core principles like memory management, stack vs. heap, and how polymorphism works internally. Mastering these advanced topics can be the key difference between landing the job and missing out.
Structure of the blog
This blog is designed to help you avoid my mistakes and take your next interview prepared and confident. It’ll cover 20 of the most commonly asked C++ interview questions, breaking down each answer so you understand the “what” and the “why.” From the basics of object-oriented programming to advanced topics like smart pointers and memory management, this guide will be your go-to resource as you prepare to ace your next C++ interview.
1. Basic C++ questions
Let’s start with some fundamental questions that will help you understand the core features of C++ and set a solid foundation for more advanced topics.
Question 1: What are the basic features of C++?
Feature | Description |
---|---|
Encapsulation | Bundles data and methods into a single unit, ensuring better data protection. |
Classes and objects | Classes are blueprints for creating objects, enabling organized code. |
Object-oriented programming | Emphasizes using objects and classes for structuring code. |
Inheritance | Enables new classes to be created from existing ones, promoting reusability. |
Polymorphism | Allows treating objects of different classes as objects of a common base. |
Question 2: What is the difference between C and C++?
Aspect | C | C++ |
---|---|---|
Programming paradigm | Procedural | Supports both procedural and object-oriented programming (OOP) |
Standard library | Limited standard functions | Extensive standard template library (STL) |
Memory management | Manual memory management | Supports constructors, destructors, and smart pointers |
Overloading | Not supported | Function and operator overloading supported |
Type checking | Less strict | Stronger type checking mechanisms |
Question 3: What are the data types in C++?
Data Type Category | Examples | Description |
---|---|---|
Primitive | int, float, char, bool | Basic types representing fundamental data |
Derived | Arrays, pointers, references | Types derived from primitive types |
User-defined | Structures, unions, classes | Custom types, which are created by users for specific use cases |
Question 4: Explain the concept of pointers in C++.
Pointers are variables that store the memory address of another variable. They are a powerful feature of C++ that enables efficient memory management and facilitates complex data structures like linked lists, trees, and graphs. Here’s why pointers are important:
- Memory access: Pointers allow direct access to memory locations, which can be essential for certain applications, such as working with hardware or optimizing performance.
- Dynamic memory allocation: By using pointers with functions like
new
anddelete
, you can dynamically allocate and deallocate memory, giving you control over resource usage. - Pass by reference/pointer: In C++, you can pass variables to functions by reference or pointer instead of by value. This approach improves performance, particularly when dealing with large data structures, by avoiding unnecessary data copying.
The following illustration will show you how a pointer holds the address of a variable:

Pointers in C++
Question 5: What is the this
pointer in C++?
The this
pointer is a special pointer in C++ that is automatically passed to every non-static member function of a class. It points to the object for which the member function is called. Here’s what it does:
- Access object members: Inside a member function,
this
can be used to access the object’s data members and member functions. - Handle ambiguity: It helps resolve ambiguity when member names conflict with function parameters or local variables.
- Return current object: The
this
pointer can be used to return the current object from a member function, enabling method chaining in C++ (e.g.,return *this
).
Let’s dive into some key OOP-related questions to deepen your understanding of how C++ uses object-oriented principles.
2. Object-oriented programming (OOP) related questions
Let’s dive into some key OOP-related questions to deepen your understanding of how C++ uses object-oriented principles.
Question 6: What is the difference between structure and class in C++?
In C++, the difference between structures and classes lies in their access specifiers:
- Structure: Members of a structure are public by default.
- Class: Members of a class are private by default.
Code example
C++
Real-world example
The Employee
structure can be compared to a company directory where basic information, such as employee ID and name, is publicly accessible, allowing anyone to view or modify these details without restrictions, as all struct
members are public by default. On the other hand, the Manager
class resembles an HR system that stores sensitive data, like performance reviews or salary details. Access to this information is restricted, and only authorized personnel (specific functions) can modify or view these details because class members are private by default and can only be accessed through controlled functions like setId
and getId
.
Question 7: What is inheritance and its types in C++?
Inheritance allows a class to inherit properties and methods from another class. There are four types of inheritance in C++:
- Single inheritance: Inheritance from one base class
- Multiple inheritance: Inheritance from more than one base class
- Multilevel inheritance: A class inherits from another derived class
- Hybrid inheritance: A combination of multiple and multilevel inheritance
Code example
Real-world example:
Imagine an ElectricCar
class inheriting basic functionality from a base Vehicle
class, such as start()
and stop()
. This represents single inheritance, where ElectricCar reuses common vehicle behaviors. Now, consider a FlyingCar
class that inherits from both Car
and Aircraft
classes. Here, the FlyingCar
would gain functionalities of both driving on roads (from Car
, like drive()
) and flying in the air (from Aircraft
, like fly()
), showcasing multiple inheritance where a single class can inherit characteristics from more than one base class.
Question 8: What is polymorphism in C++?
Polymorphism allows the same function or operator to behave differently based on the object it’s acting upon. It comes in two forms:
- Compile-time polymorphism (Static polymorphism): Achieved through function or operator overloading.
- Runtime polymorphism (Dynamic polymorphism): Achieved through inheritance and virtual functions.
Code example
Real-world example
Compile-time polymorphism could be used in a payment system to handle data types (e.g., credit card numbers, PayPal IDs) with overloaded functions. Runtime polymorphism ensures that the right processPayment()
method is invoked depending on whether the object is a CreditCardPayment
or PayPalPayment
object.
Question 9: 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, making data more secure.
Code example
Real-world example
Think of a bank account system. The balance
is private, meaning it cannot be directly modified. Only authorized methods, such as deposit()
and withdraw()
, can change the balance, protecting sensitive data from unauthorized access.
Question 10: What is abstraction in C++?
Abstraction is the concept of hiding the internal details of a system and exposing only essential functionalities. In C++, abstraction is achieved through abstract classes and interfaces (pure virtual functions).
Code example
Real-world example
In graphics software, the user doesn’t need to know how a shape is drawn internally. They only use the draw()
function to render the shape on the screen, with the actual implementation hidden behind the abstraction.
3. Advanced C++ questions
Let’s explore advanced C++ concepts crucial for mastering the language and excelling in technical interviews.
Question 11: What are templates in C++?
Templates in C++ allow you to write generic and reusable code. They enable functions and classes to operate with different data types without rewriting code for each type. There are two main types of templates:
- Function templates: Allows creating a function that can operate on different data types.
Example
Function template
- Class templates: Allow classes to operate with any data type.
Example
Class template
Real-world example
In an actual e-commerce platform, such a design can handle carts with any type of product (books, electronics, groceries, etc.) without needing separate implementations for each product type. Templates
allow the system to scale and adapt as more types of items are added, reducing code duplication while maintaining flexibility.
Question 12: What is the difference between deep copy and shallow copy?
A shallow copy duplicates an object but not the objects it points to, meaning both copies will share the same memory addresses for any pointer data members. On the other hand, a deep copy creates a new copy of the object and all the objects it references, ensuring complete separation.
Shallow copy example
Shallow copy
Deep copy example
Deep copy
Real-world example
Deep copying is crucial when handling dynamic memory allocation to avoid unexpected modifications when working with object copies, especially in data processing or graphics rendering cases.
Question 13: What is a virtual function in C++?
A virtual function is a member function in a base class declared with the virtual
keyword, allowing it to be overridden in derived classes. It ensures that the correct function is called for an object, regardless of the type of reference (or pointer) used to call the function. Virtual functions enable runtime polymorphism.
Code example
Virtual function in C++
- VTable (Virtual table): A table that stores addresses of the class’s virtual functions.
- VPointer (Virtual pointer): A hidden pointer within each class object points to the VTable.
Real-world example
Virtual functions are commonly used in software design patterns like the Strategy pattern, where an object’s behavior can be changed at runtime based on which derived class it points to.
Question 14: What is the use of the mutable
keyword in C++?
The mutable
keyword allows a class member to be modified even if it is part of an object declared as const
. This is useful for members that are meant to be updated internally without affecting the logical constancy of the object.
Code example
‘mutable’ keyword in C++
Real-world example
A logger class might use mutable
to keep track of the number of times a log is printed, even if the logger object itself is declared const
.
Question 15: What is the RAII principle in C++?
RAII (Resource acquisition is initialization) is a programming idiom that ensures resources are properly acquired and released. It ties the resource life cycle to the object’s lifetime, meaning resources are acquired in the constructor and released in the destructor.
Code example
RAII principle in C++
Real-world example: RAII is commonly used in managing resources such as file handles, database connections, and mutex locks in multi-threaded programming. It helps prevent resource leaks by ensuring that resources are properly cleaned up when the associated object goes out of scope.
4. Memory Management and Performance Questions
Let’s delve into some crucial questions about memory management and performance optimization techniques in C++, which are essential for writing efficient and safe code.
Question 16: What are smart pointers in C++?
Smart pointers are a safer alternative to traditional pointers in C++. They help manage the lifetime of dynamically allocated objects and automatically deallocate memory when the object is no longer in use, reducing the risk of memory leaks.
unique_ptr
: Owns an object exclusively. It cannot be copied, only moved, ensuring only one pointer can manage the resource at any time.
Code example
unique_ptr in C++
shared_ptr
: Allows multiple pointers to share ownership of an object. It maintains a reference count and deallocates the object when the count reaches zero.
Code example
shared_ptr in C++
weak_ptr
: Used withshared_ptr
to hold a non-owning reference to the object, preventing circular references that could cause memory leaks.
Code example
weak_ptr in C++
Real-world example
To ensure proper cleanup, smart pointers are commonly used in resource management, such as managing database connections, file handles, and network sockets.
Question 17: What is the difference between malloc()
and new
in C++?
malloc()
: It’s a C library function that allocates memory on the heap but does not call constructors for object initialization. Memory allocation must be manually deallocated usingfree()
.
Code example
malloc() in C++
new
: It’s a C++ operator that allocates memory and calls the constructor to initialize objects. Memory is deallocated using thedelete
operator.
Code example
new operator in C++
Real-world example
new
is preferred in C++ for object-oriented programming as it handles allocation and initialization, whereas malloc()
is primarily used in legacy C codebases.
Question 18: What are destructors in C++?
A destructor is a special member function of a class that is automatically called when an object goes out of scope or is explicitly deleted. It releases resources, such as closing file streams or deallocating memory.
Code example
Destructors in C++
Real-world example
Destructors are vital in managing resources like file handles, database connections, and sockets, ensuring they are properly closed when no longer needed.
Question 19: How does dynamic memory allocation work in C++?
Dynamic memory allocation allows programs to allocate memory at runtime from the heap, unlike stack memory, which is limited and automatically managed.
- Heap: Large pool of memory managed manually. Used for objects that need to persist beyond the function call.
- Stack: Fast but limited memory used for function call management. Automatically deallocates memory when the function exits.
Code example
Dynamic memory allocation work in C++
Real-world example
Dynamic memory allocation is commonly used in applications that require large and flexible data storage, such as graphics rendering engines, where the exact amount of memory needed is only known at runtime.
Question 20: What is the use of static_cast
, dynamic_cast
, const_cast
, and reinterpret_cast
?
C++ provides four types of type casting operators:
static_cast
: Used for converting between related types, such as convertingint
tofloat
or downcasting pointers within the same class hierarchy.
Code example
static_cast in C++
dynamic_cast
: Used for safely casting pointers and references within an inheritance hierarchy. It checks the validity of the cast at runtime.
Code example
dynamic_cast in C++
const_cast
: Used to add or remove theconst
qualifier from a variable.
Code example
const_cast in C++
Note: Modifying a const
variable using const_cast
leads to undefined behavior. While the code will compile and run, it’s generally unsafe and should be avoided in real applications.
reinterpret_cast
: Reinterprets the bits of a type as another type without any safety checks. It’s used for low-level, unsafe conversions.
Code example
reinterpret_cast in C++
Real-world example
These casts are essential in low-level programming, such as systems development, graphics programming, or when interfacing with hardware where specific data reinterpretation is required.
5. Tips to ace C++ interviews in 2024
Let’s explore some effective tips to help you excel in C++ interviews and stand out as a top candidate.
Research the company’s tech stack
Understanding the company’s tech stack is crucial for tailoring your interview preparation. Research how the company uses C++—for system development, embedded systems, game development, or finance. For instance, if the company focuses on embedded systems, you should be well-versed in low-level memory management, real-time constraints, and performance optimization in C++. Tailoring your preparation to their specific domain will show your proactive approach and make you stand out as a candidate who understands the practical application of C++ in their business.
Example tip
If interviewing at a game development company, emphasize your knowledge of C++’s performance aspects, multithreading, and graphics programming libraries like DirectX or OpenGL.
Brush up on data structures and algorithms
A solid understanding of Data Structures and Algorithms (DSA) is just as important as knowing C++ syntax. Many interview questions will test your problem-solving skills and ability to use the right data structure for a given scenario. You’ll often encounter questions about arrays, linked lists, trees, stacks, queues, hash maps, and algorithms like sorting, searching, and dynamic programming.
Example tip
Focus on optimizing your code’s time and space complexity, and practice implementing algorithms in C++. Understanding how to manipulate pointers, manage memory, and optimize recursive functions is crucial, especially in competitive coding environments.
Practice coding challenges
Hands-on practice is essential for mastering C++ interview questions. We include many problems in the course below to help you sharpen your C++ skills. Start with easy problems to build confidence and gradually move on to more complex challenges.
Grokking the Coding Interview Patterns in C++: The ultimate guide to coding interviews in C++, Grokking the Coding Interview Patterns in C++ teaches proven strategies developed by FAANG engineers to get interview-ready in just a few hours.
Example tip
Regularly participate in coding problems to improve your problem-solving speed and learn how to tackle new and unexpected challenges. This will prepare you for the technical aspects of the interview and train you to think quickly under pressure.
6. Conclusion
Throughout this blog, we’ve covered the essential C++ concepts and questions you will likely encounter in interviews. From basic C++ features like classes and pointers to advanced topics such as smart pointers, polymorphism, and memory management, this guide equips you with the knowledge to tackle beginner and advanced-level questions. We also highlighted the importance of understanding object-oriented programming principles, dynamic memory allocation, and the various types of casting in C++—all critical for mastering the language and impressing interviewers.
If you found this guide helpful, don’t stop here! Explore our other blogs on data structures, algorithms, and advanced C++ techniques to deepen your understanding.