C++ Interview Questions and Answers

C++ is a powerful, high-performance programming language developed by Bjarne Stroustrup at Bell Labs in 1979. As an extension of the C language, it introduces object-oriented features while retaining C’s efficiency and low-level capabilities. 

C++ offers great flexibility through support for both object-oriented and generic programming, making it well-suited for game development, system programming, and applications that require high performance and resource control.. C++ is highly popular because of its speed, efficiency, and strong compatibility with both low-level system components and legacy C code.

Table of Contents:

• • • Basic C++ Interview Questions
    • Intermediate C++ Interview Questions
    • Advance C++ Interview Questions(3 to 7 Years)
    • OOPs in C++ Interview Questions
    • C++ Developer Interview Questions

Basic C++ Interview Questions

Let’s start with C++ interview questions for freshers to help a candidate learn basic concepts that are the building blocks of C++. These C++ basic questions test your problem-solving skills and familiarity with C++ features. Brushing up on these concepts may help you to revise the concept.

1. What is C++?

C++ is a high-performance programming language that extends the C language, with additional features like object-oriented programming. It supports multiple programming paradigms, including procedural, object-oriented, and generic programming, making it highly versatile.

C++ is widely used in performance-critical applications, including:

• Game development for building game engines and high-performance graphics.
• System software such as operating systems, device drivers, and embedded systems.
• Real-time applications include robotics, automotive systems, and financial trading platforms.
• Desktop applications like Adobe products and other software require speed and efficiency.
• High-performance computing for simulations, scientific computing, and large-scale systems.

2. What is a namespace in C++?

In C++, the namespace helps in organizing the code and avoids naming conflicts among identifiers such as variables, functions, and classes. It acts as a container that groups related elements under a common name. 

A namespace is defined by using the keyword namespace and the scope resolution operator(::). For example, the C++ Standard Library is encapsulated within the std namespace, so standard input/output functions like cin and cout are accessed as std::cin and std::cout. Namespaces help avoid ambiguity in large projects.

3. What are the differences between C and C++?

C is a procedural programming language, whereas C++ supports both procedural and object-oriented programming paradigms. The following differences will help clarify the distinctions  between C and C++: 

4. Define a class in C++.

In object-oriented programming (OOP), a class serves as a blueprint or template for creating objects. It defines a new data type by specifying the attributes (member variables) to store data and behaviors (member functions)  associated with that type. A class determines the data an object holds and the operations that can be performed on it.

5. Describe what an ‘object’ is.

It is a fundamental concept in object-oriented programming. The object is an instance of a class, created based on the blueprint provided by the class. In simpler terms, an object is a real-world entity that has a state (attributes/data) and behaviour (methods/functions).

6. Please explain what ‘constructor’ and ‘destructor’ mean.

• Constructor: A constructor is a special member function in a class that is automatically invoked when an object of the class is created. It is used to initialize the data members of the object or perform any setup operations required before the object is used. The constructors share the same name as the class and do not have a return type, not even void.
• Destructor: A destructor is a special member function that is automatically called when an object goes out of scope or is explicitly deleted. It is used to perform clean-up activities, such as releasing memory or other resources acquired by the object during its lifetime. Destructors start with tilde (~) and have the same name as the class, with no parameters and return type.

7. What do you mean by copy constructor?

A copy constructor in C++ is a special constructor that is used to create a new object by copying an existing object of the same class. This constructor is automatically invoked when an object is initialized using another object of the same type.

8. What are the types of inheritance?

In object-oriented programming, inheritance is the process where one class can use the properties and behaviors of another class. It promotes code reusability and allows subclasses to build on and customize the features of a parent class, creating a clear class hierarchy.

There are several types of inheritance:

1. 1. Single Inheritance: A class inherits from only one parent class, by reusing its properties and behaviours. 

2. Multilevel Inheritance: Multilevel inheritance occurs when there is inheritance of a class by a derived class, so that there is a chain of inheritance. The last class in the chain is able to access attributes and methods of all ancestor classes.

For example:

3. Multiple Inheritance: A class can inherit from multiple base classes. 

4. Hierarchical Inheritance: Multiple derived (child) classes inherit from the same base (parent) class.

For example:

5. Hybrid (or Virtual) Inheritance: A combination of multiple and multilevel inheritance. 

Example: 

9. What is Operator overloading?

Operator overloading in C++ allows you to redefine the way operators work for user-defined types, such as classes and structures. This allows your objects to behave like built-in data types and perform customized actions when standard operators are applied to them.

For example, when you add two integers using the “+” operator, it performs standard addition. However, by overloading the “+” operator for your custom class, you can define how the addition should be performed for objects of that class.

Operator overloading lets you define custom behavior for operators when they are used with class objects. This allows your user-defined types to behave more like built-in types, improving code readability and usability. In such cases, you create a special function called an operator function to define the operator’s behavior. 

For binary operators (that work with two operands), the operator function accepts one explicit parameter representing the right-hand operand.  The left-hand operand is the object that calls the function.

Here’s an example of operator overloading for a custom Complex class to perform addition and output using the + and  << operators:

Explanation: In this example, the “+” operator is overloaded for the Complex class to perform the addition of two Complex objects. The operator+ function takes another Complex object as its parameter, and returns a new Complex object representing the sum of the two.

10. What is meant by the const keyword?

The “const” keyword in the C++ programming language indicates that the value is a constant and cannot be altered after initialization. When used with a variable, it ensures that the variable’s value remains constant throughout its lifetime. Attempting to modify a “const” variable will result in a compilation error. 

Using const enhances data integrity and code readability by clearly signaling that a value should not be altered. It also helps prevent accidental changes and can enable certain compiler optimizations, potentially improving the performance and reliability of your code.

11. What do you mean by Call by Reference?

Call by reference is a method of passing arguments to a function, where instead of passing the actual value, the memory address of the original variable is passed. This allows the function to directly access and modify the original variable in the calling code.

In call by reference, the function parameter is specified as a reference to the variable’s data type. For example, in C++, this can be done using the ampersand symbol (&). This ensures that any changes made to the parameter inside the function are reflected in the original variable.

Some programming languages use special syntax to indicate reference passing, while in others, it may be the default behavior for function arguments.

Let’s see an example of call by reference in C++:

In this example, the incrementByReference() function takes an integer parameter, num, by reference. When the function is called with the variable num from the main() function, any changes made to num inside the incrementByReference() function will directly affect the original variable in the main() function.

12. What does Call by value mean?

In C++, “call by value” is a parameter passing method where a copy of the actual argument’s value is passed to the function’s formal parameter. As a result, any modifications made to the parameter inside the function do not affect the original argument outside the function. 

Call by Value ensures data encapsulation and prevents unintended changes to the original data. However, it may lead to increased memory usage, especially when large objects are copied. Call by value is the default parameter passing method in C++, providing a safe and isolated environment for function execution without altering the caller’s variables.

13. What are access specifiers? 

In C++, access specifiers are used to define the accessibility of class members and ensure the security and encapsulation in object-oriented programming. 

There are three main access specifiers: 

• Public: Member functions and data members declared as public are accessible outside the class where the object is visible.
• Private: Data members and member functions declared as private are accessible only within the same class.
• Protected: Member functions and data members declared as protected are similar to private, but they can also be accessible within the same class and to derived (child) classes.

14. What is an abstraction in C++?

Abstraction is a fundamental concept in object-oriented programming (OOP). It is the process of exposing only the essential features of an object to the user while hiding the irrelevant or complex implementation details. It allows developers to create real-world entities more effectively by focusing on key attributes and behaviors. 

In C++, abstraction is achieved using abstract classes and pure virtual functions. Abstraction simplifies code, improves maintainability, and helps manage the complexity of large systems by allowing developers to work at a higher conceptual level. 

There are two types of Abstraction:

• Control abstraction
• Data abstraction

15. What do C++ comments mean?

In C++, comments are used to add explanations or notes within the source code. The compiler ignores comments, and they have no effect on the program’s execution. Comments act as internal documentation, making the code easier to understand for others or even for the original developer when revisiting the code later.

In C++, comments are of two types:

• Single-line comments: Start with // (double forward slash), and extend to the end of the line. Everything after // on that line is treated as a comment and ignored by the compiler.
  Syntax Example:
  
  

// This is a single-line comment

int a = 10;  // declaring and initializing a variable

• Multi-line comments: These comments are enclosed between /* and */, they can span multiple lines, allowing you to add longer explanations or temporarily disable blocks of code.
  Syntax Example:
  
  

/* This is a multi-line comment.

It can span across multiple lines.

Useful for explaining logic in detail. */

int b = 20;

16. What distinguishes variable declaration from variable definition?

In C++, the declaration and definition of a variable are two distinct concepts:

Declaration: A variable declaration informs the compiler about the variable’s name and data type, but does not allocate memory for it. It essentially signals that the variable exists, allowing it to be used across different parts of the program. Declarations can appear multiple times, often in header files or using the extern keyword.

E.g.: extern int age; // Variable declaration

Definition: A variable definition both declares the variable and allocates memory for it. It links the variable name to a specific memory location where the data will be stored. A variable must be defined exactly once in a program (unless it’s declared as “extern” and defined in another file or translation unit).

E.g.: int age = 30; // Variable definition

17. What is the difference between the scope of a global and a local variable?

Global Variable Scope: A global variable is defined outside of all functions and classes, making it accessible and modified from anywhere in the program, including within functions, classes, or blocks.

As global variable scope exists for the entire lifetime of the program, global variables can be used for sharing data across multiple parts of the code.

Local Variable Scope:

A local variable is defined inside a function or a block, and can only be accessed within the specific scope. It exists only during the execution of that block or function, and is destroyed once the control exits the scope.

Local variables ensure data encapsulation and prevent unintended interference from other parts of the program.

18. What are C++ data types? 

In C++, the data types specify the kind of data a variable can hold. The data types are efficient for memory management and data manipulation. C++ data types are categorized as follows:

Primitive or built-in data types: 

1. Int (integer): Stores the numbers. 
2. Float (floating-point): Stores the decimal numbers.
3. Double (double precision-floating point): Stores the large decimal numbers. 
4. Char (character): Stores a single character. 
5. Bool (boolean): Stores true or false, used for logical operators. 

Derived data types: 

1. Array: A collection of multiple values of the same type. 
2. Pointer: It stores the memory address of a variable. 
3. Reference: It behaves as an alias for another variable. 

User-defined data types: 

1. Struct: It groups multiple types of variables under one name. 
2. Class: It defines the object in an object-oriented programming language.
3. Enum: Assigns meaningful names to integer constants. 
4. Union: A union stores different data types under the same memory location. 

Modifiers: 

Signed, unsigned, short, long: Used to adjust the size and sign of the numeric data types. 

19. How can you access the global variable if it shares the same name as a local variable?

If a global variable shares the same name as a local variable, you can access the global variable using the scope resolution operator “::”.

Example: 

20. Define a token in C++

A token in C++ is generally the smallest element of any program that has some meaning to the compiler. At the time of the lexical analysis, the source code is broken down into a sequence of tokens for parsing.

Types of tokens:

• • Keywords: if, return, class, etc.
  • Identifiers: Variable and function names like x, myFunc.
  • Literals: Constants like 42, ‘A’, 3.14.
  • Operators: +, ==, -, etc.
  • Punctuation: ;, {, }, ,, etc.

21.  What is the difference between function overloading and operator overloading?

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22. What is an abstract class, and when do you use it?

An abstract class in C++ is a class that typically contains at least one pure virtual function. A pure virtual function is declared by appending = 0 to the function declaration.

Key Points:

• • • Abstract classes cannot be instantiated.
    • They act as blueprints for derived classes.
    • Enforce a common interface among subclasses.

Use abstract classes when designing polymorphic base classes.

Code Example:

23. What are the concepts in C++20? How do they improve template readability?

24. What are C++ modules, and how do they improve compilation?

C++ Modules were launched in C++20 to reduce compile times and expand project scalability. The traditional way of C++ uses header files, which get parsed repeatedly during compilation. This process is inefficient, and more importantly, it is inefficient for large projects. Modules address this problem by permitting you to import compiled interfaces directly.

Advantages:

• • • Faster compilation (gets rid of the redundant parsing process).
    • More encapsulation and better separation of concerns.
    • The presence of multiple inclusions and the occurrence of macros are no longer an issue.

Example:

// math.ixx
export module math;
export int add(int a, int b) {
    return a + b;

}
// main.cpp
import math;

#include <iostream>
int main() {
    std::cout << add(3, 4);
    return 0;
}

Modules make it more manageable for large codebases to be maintainable and build processes more efficient.

25. How does std::optional differ from std::expected?

std::optional and std::expected are quite similar in that both serve the purpose of handling values that can either be present or absent. The way they communicate absence is the distinction between them:

• std::optional: Represents a value that can be provided, or it may not be there. If the value is there, no information is given about the reason.
• std::expected<T, E>: Supplies either a correct answer (T) or an error (E), thus allowing the problem to be known when a value is not given.

Use Cases:

• Optional is suitable for values that can be optionally provided (e.g., optional return types).
• Expected should be utilized for the management of errors and providing the results along with the error context.

Example (C++23):

std::expected<int, std::string> divide(int a, int b) 
{
    if (b == 0) return std::unexpected("Division by zero");
    return a / b;
}

26. What is the difference between a struct and a class?

In C++, struct and class are almost identical. The key difference lies in default access specifiers.

Example:

struct Point {
    int x, y; // public by default
};

class Circle {
private:
    int radius;
};

Use struct for passive data structures and class for encapsulated, behavior-rich types.

27. What do you know about the friend class and the friend function?

The friend keyword typically allows a function or another class to access private and protected members of a class.

Use Cases:

• They allow two classes to access each other’s internals.
• Generally, they are helper functions that need access to private data.

Example:

class Box {
    friend void printVolume(const Box&);
private:
    int volume = 100;
};
void printVolume(const Box& b) {
    std::cout << b.volume;
}

Use friend sparingly, as it breaks encapsulation and should be reserved for tightly coupled components

28. What are member functions?

Member functions in C++ are functions defined within a class that operate on the class’s objects. They are an integral part of object-oriented programming (OOP), enabling encapsulation by providing controlled access to the data members of the class.

Member functions define the behavior of class instances and allow objects to interact with their internal data in a structured and secure manner. These functions can have different access specifiers, such as public, private, and protected, which determine how and where they can be accessed.  Member functions include special types such as constructors, destructors, and operator overloading, which enhance object creation, cleanup, and flexibility in operations.. 

Overall, member functions play a crucial role in implementing data abstraction, integrity, and modularity, allowing for well-organized, maintainable, and reusable code within class hierarchies. 

29. What is an inline function?

An inline function in C++ is a special type of function where the compiler replaces the function call with the actual code of the function during compilation. This is often used with small, frequently called functions, especially within classes, to reduce the overhead of function calls.

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30. What is an object-oriented programming language, and also are its features? 

Object-oriented programming (OOP) is a programming paradigm that organizes code around objects rather than functions. These objects represent real-world entities that encapsulate both data and behaviour within a single unit. 

The six core features of OOP are:

1. Encapsulation: Bundling the data and methods that operate on that data into a single unit, typically a class, is known as encapsulation. It protects the sensitive information by making class variables private and exposing access through public getter and setter methods. This ensures better control over data and enhances security.
2. Abstraction: Abstraction is the process of exposing only essential features of an object to the user while hiding the internal implementation details. Abstraction is achieved by using abstract classes and pure virtual functions. 
3. Inheritance: Inheritance refers to a process where one class (subclass/derived class) can inherit the properties and behaviours of another class (superclass/base class).
4. Polymorphism: The word polymorphism means “many forms” (poly = many, morphism = forms) and allows the same operation to behave differently on different classes or objects. It is achieved through method overloading and method overriding to provide flexibility in code. 

The above principles help in the creation of modular, reusable, and maintainable code by structuring programs around objects.

31. What is dynamic binding in C++?

Dynamic binding in C++, which is also known as late binding, generally means the process where the method that is going to be executed is determined at runtime, rather than at compile time.

This typically occurs when you are employing pointers or references to base classes to call virtual functions that are overridden by derived classes.

32. What is multithreading in C++?

In C++, multithreading is a feature that enables the concurrent execution of multiple threads in a single program. Multithreading enables the parallel execution of different tasks, improving performance and responsiveness. By running threads independently, multithreading helps make efficient use of available system resources, especially on multi-core processors.

33. What is the purpose of the auto keyword in C++?

In C++, the auto keyword is used to automatically deduce the data type of a variable at compile time based on the value it is initialized with. This is especially useful for complex or lengthy data types, making the code cleaner and easier to read. Using auto enhances flexibility, reduces redundancy, and improves overall code maintainability. 

 auto num = 10;   // Deduces as int

auto pi = 3.14;  // Deduces as double

auto b = 'c';    // Deduced as char

auto c = true;  // Deduced as bool

34. What is message passing?

In object-oriented programming (OOP), message passing is a fundamental concept that enables objects to communicate and interact by sending and receiving information. This promotes encapsulation, modularization, and code reusability. Message passing occurs when one object calls a member function of another object, enabling the transfer of data or the triggering of behavior between objects in a structured and organized manner.

35. Why do we use iostream at the beginning of every program?

Including the iostream header at the beginning of every C++ program provides access to standard input and output stream objects. This enables the use of cout for displaying output on the console and cin for receiving input from the user. By importing this header, you ensure that essential I/O operations are supported throughout the program.

36. What is the use of <stdio.h>? 

In C++, the <stdio.h> header file is inherited from the C language and stands for Standard input/Output header. It contains declarations for fundamental functions like printf, scanf, and getchar, which are used to perform input and output operations via the console.  These functions facilitate interaction between the user and the program by allowing data to be read from and written to the standard input/output streams. Although C++ offers its own I/O library (iostream), including <stdio.h> in a C++ program allows the use of traditional C-style I/O functions when needed, offering flexibility and compatibility with legacy code.

37. Why is <string.h> used in C++ programs?

The<string.h> header file is used in C++ to provide access to a set of functions for performing various string manipulation tasks. It contains function prototypes that facilitate operations like copying, concatenation, comparison, and searching of C-style strings. These functions are essential when working with raw character arrays, allowing efficient and standardized handling of text-based data in C++ programs.

38. What are Arrays?

In C++, an array is a data structure used to store a fixed-size sequence of elements of the same data type. Before C++20, arrays were commonly used for storing a known number of items, as their size must be defined at compile time and cannot change during execution. 

For dynamic-size collections, C++ offers alternatives such as std::vector from the Standard Template Library (STL). 

Vectors provide dynamic resizing capabilities, allowing the elements to be added or removed dynamically at runtime, unlike traditional arrays. They are ideal when the size of the data collection is not known in advance or needs to change during the program’s execution.

39. What are pointers?

Pointers are fundamental features in C++ that store the memory addresses of other variables. They allow direct access and manipulation of memory, providing significant flexibility and efficiency in managing data. 

Pointers are useful for tasks like dynamic memory allocation and efficient handling of large datasets, where performance and memory control are critical. 

However, improper use of pointers can lead to issues like memory leaks, dangling pointers, or segmentation faults; hence, pointers must be handled with care. When used properly, pointers allow programmers to build complex data structures, optimize memory usage, and implement low-level operations, making them essential for mastering complex C++ programming techniques.

40. Explain the reference variable.

A reference variable in C++ acts as an alias for an existing variable, allowing you to access the same memory location using a different name. Once a reference is initialized to a variable, it cannot be changed to refer to another variable.

Syntax: 

data_type& reference_variable = existing_variable;

Key points about reference variables:

• Initialization is required: When a reference variable is declared, it must be initialized with an existing variable. Once initialized, it acts as an alias for the original variable.
• No Separate Memory: Unlike pointers, reference variables do not create a new memory location. They simply provide another name for the same memory location as the original variable.
• No Null Reference: Unlike pointers, reference variables cannot be null. They must always refer to a valid object.
• No Reassignment: A reference variable, once initialized with a variable, cannot be re-initialized to refer to another variable. Its lifetime is tied to the original variable.
• No Size Overhead: References do not consume extra memory. They are implemented by the compiler as addressed by direct memory.
• Useful for Function Parameters: References are commonly used as function parameters to achieve call-by-reference behavior, in which functions can update their original variables passed as parameters.

43. What is the purpose of the malloc() and calloc() functions in C++?

The malloc() and calloc() functions in C++ are used for dynamic memory allocation at runtime, allowing you to reserve memory on the heap. Once the allocated memory is no longer needed, the free() function is used to release it and prevent memory leaks.

The table below summarizes the key differences between calloc() and malloc(): 

44. What is function prototyping?

Function prototyping in C++ involves declaring a function’s signature or interface before its actual definition. It informs the compiler about the function’s name, return type, and parameter types, enabling it to perform type-checking and ensure correct function calls during compilation. Note that a prototype does not include the function body.
The function prototype is typically placed at the beginning of the source file or in a header file, especially when functions are called before their full definitions appear in the code.

The syntax for function prototyping is as follows:

return_type function_name(parameter1_type parameter1_name, parameter2_type parameter2_name, ...);

45. What is a default argument in C++?

A default argument in C++ is a value assigned in a function definition or declaration that is automatically used if the caller does not supply a corresponding argument. It allows a function to be called with fewer arguments, improving flexibility and simplifying function calls.

Default arguments are typically specified in the function prototype or definition. They help reduce code duplication and make functions more versatile.

Code example:

46. What are the differences between shallow copy and deep copy? 

47. How can a member function be defined in C++?

A member function can be defined in two ways:

• • Outside the class definition
  • Inside the class definition

48. What are smart pointers in C++? 

In C++, smart pointers are objects that automatically manage the memory of dynamically allocated objects. Smart pointers ensure that resources are released when no longer needed and help in avoiding memory leaks. Commonly used smart pointers are unique_ptr, shared_ptr, and weak_ptr

Code Example:

49. What do getdata() and putdata() mean?

getdata() and putdata() are commonly used function names for handling input and output operations within classes. 

getdata(): The getdata() function is used to receive input from a user or an input source and store the data in variables or data members of a class. The main purpose of getdata() is to collect the necessary data required for processing.

putdata(): The putdata() function is used to output or display data to a destination such as a file or a console. It presents the processed or stored data, making it available for the user or for saving.

50. How is memory allocated to objects?

In C++, memory is not allocated when a class is defined. Instead, memory is allocated only when an object of that class is created. The class definition simply serves as a blueprint, and actual memory for its data members is reserved only during object instantiation.

51. What is RAII in C++? 

RAII (Resource Acquisition Is Initialization) in C++ is a programming technique where resources such as memory, file handles, or locks are acquired during object initialization and automatically released when the object goes out of scope. The resource is typically allocated in the constructor and cleaned up in the destructor, ensuring proper management and preventing resource leaks.

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52. What are static data members?

A data member can be declared as static in C++, meaning it belongs to the class rather than any specific object. A static member is initialized only once, typically to zero, when the first object of the class is created. No further initialization is allowed. 

Only one shared copy of the static member exists, and it is shared by all instances of the class. Although it is part of the class, it remains accessible only through the class or its objects, depending on its access specifier.

53. What are static member functions?

The static member functions are similar to static data variables. The static member functions have the following properties:

1. A static member function can only access other static members.
2. A static member function can be called using the class name.

54. What do you mean by constructors in C++?

A constructor is a special member function that is automatically invoked when an object of a class is created. It has the same name as the class, and is used to initialize the object’s data members and set up its initial state. Constructors ensure that objects begin their lifecycle in a valid and predictable state.
Code Example:

56. What do you mean by parameterized constructors?

Parameterized constructors are constructors that accept arguments, allowing you to initialize objects with specific values at the time of creation.

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57. What are the different ways to pass parameters in C++?

There are three methods in C++ to pass parameters to functions:

58. How can we initialize values as arguments to the constructor function when an object is declared?

We can initialize values as arguments to the constructor function when an object is declared in two ways:

1. By calling the constructor explicitly.
2. By calling the constructor implicitly.

Code Example:

59. Can a copy constructor accept an object of the same class as a parameter, instead of a reference to the object?

No, the copy constructor cannot take a parameter of an object of the same class as a parameter. If it does, it would call the copy constructor once again to pass the object, resulting in infinite recursion and eventually a stack overflow. This is why a copy constructor should take the parameter by reference, usually in the following manner:

 
ClassName(const ClassName &obj);

60. What are virtual destructors?

Virtual destructors in C++ are essential in class hierarchies involving polymorphism. If a base class is intended to be inherited and used through pointers or references, its destructor should be declared as virtual to ensure proper cleanup.
Without a virtual destructor, deleting a derived class object through a base class pointer results in undefined behavior the derived class’s destructor may not be called, potentially causing resource leaks. By making the base class destructor virtual, C++ ensures that the destructors of derived classes are correctly invoked in the right order, enabling safe and predictable destruction of objects.

Let’s consider a scenario with a base class Shape and a derived class Circle:

In this case, when the delete shape is executed, only the destructor of the Shape class is called because the pointer shape is of type Shape and the Shape does not have a virtual destructor. As a result, the destructor for the Circle class is not called. This can lead to memory leaks or improper resource cleanup, as any resources managed by the Circle class are not released.

To fix this problem, the destructor in the base class should be declared as virtual:

class Shape {
public:
     Shape() {
        std::cout << "Shape constructor"<<endl;
    }

    virtual ~Shape() { // Virtual destructor
        std::cout << "Shape destructor"<<endl;
    }
};

When a virtual destructor is used in the base class, deleting a derived class object through a base class pointer ensures that destructors are called in the correct order from the derived class up to the base class. This guarantees that all resources allocated by both the derived and base classes are properly released, preventing memory leaks and ensuring safe object destruction in a class hierarchy.

61. How can I handle a constructor that fails?

In C++, a constructor does not return a value, and hence it has to throw an exception on failure. In case something goes wrong with regards to the initialization of the object, the constructor must throw an exception with the help of the throw keyword. This allows the program to transfer control to an appropriate exception handler. 

Use the try-catch block to catch the exception and handle the failure gracefully. Inside the catch block, implement error-handling mechanisms, such as displaying an error message, logging, or taking corrective actions. Properly handling constructor failures ensures robustness and maintains the integrity of the program, preventing unexpected crashes or undefined behavior.

62. What is Stack unwinding?

Stack unwinding in C++ is what occurs when there is propagation of exceptions backward through a call stack. The program deletes automatically constructed locals made within the current and called functions at that point, in reverse of building them.

This ensures that:

• Each of these locals correctly calls its destructors.
• Resources are released (for example, memory, file handles, etc.).
• Even when there’s error handling, the programme is leak-proof and secure.

Stack unwinding ensures exception safety by purging the stack during the propagation of the exception to a catch statement that will handle it.

63. Can we explicitly call a destructor on a local variable?

Technically, yes, you can call directly a destructor of a local variable with the syntax obj.~ClassName();. But it’s not recommended and can lead to undefined behavior, especially when the object is destroyed more than once (manually and when it goes out of scope).

In C++, an automatically stored duration is available for locals. Their destructors are automatically called when leaving the scope of the object. Manually calling the destructor may:

• Causes a crash when automatically called again by the destructor.
• Violate principles of RAII (Resource Acquisition Is Initialization).
• Against best practices for C++.

Code Example:

64. Which Operators cannot be overloaded?

Below is a list of operators that cannot be overloaded in C++:

65. What are the most popular C++ unit testing frameworks in 2025?

Top Unit Testing Frameworks:

1. Google Test (GTest)
   • Rich in features, actively maintained.
   • Supports parameterized tests, test fixtures, and mocking.
2. Catch2
   • Lightweight, header-only.
   • Supports BDD-style and single-header usage.
3. doctest
   • Very fast, suitable for embedded systems.
   • Header-only, inspired by Catch2.
4. Boost.Test
   • Comprehensive, tightly integrated with the Boost ecosystem.

Example using Google Test:

#include <gtest/gtest.h>

TEST(MathTest, AddTest) {
    EXPECT_EQ(2 + 3, 5);
}

These frameworks help ensure correctness, regression prevention, and confidence in code quality.

How to Prepare for C++ Interview Questions

Follow these important guidelines to prepare for your future C++ interview effectively:

1. Master Core C++ Concepts

• Develop a clear understanding of OOP concepts like encapsulation, inheritance, polymorphism, and abstraction.
• And don’t forget to go through the basic C++ content, including data types, control structures, pointers, and memory management.

2. Learn Modern C++ (C++11 – C++23)

• Highlight modern C++ concepts such as smart pointers, lambda expressions, move semantics, ranges, concepts, and modules.
• Stay up to date with the most recent features added to C++17, C++20, and C++23.

3. Practice Common C++ Interview Questions

Practice these C++ interview questions and answers that often appear in C++ interviews by large companies.

4. Solve Real Coding Problems

• You can enhance your C++ by working through numerous coding interview problems with online tools such as LeetCode, HackerRank, or Codeforces.
• Practice certain topics such as recursion, DP, greedy algorithms, and bit manipulation.

5. Understand STL and Templates

• Have a deep understanding of STL containers, iterators, algorithms, and template metaprogramming.
• Be familiar with the operations of std::vector, std::map, std::unordered_map, etc.

6. Prepare for System Design (Advanced Roles)

• Practice low-level system design in C++ for a senior role.
• Also, be aware of the memory arrangement, efficiency improvement, and multithreading.

7. Practice Interviews and Resume Matching

• Hold some mock sessions to get used to stress and also to improve your speaking skills during the time of your interview.
• Design your resume to include your C++ projects, contributions, and tech stack knowledge.

Please take a moment to watch the video on C++ interview questions.

Conclusion

Mastering C++ results in well-paying careers in software engineering, gaming, embedded systems, and financial sectors. Due to Java/C# and contemporary C++ innovations such as smart pointers, templates, and concepts, employers are looking for individuals who consider more than syntax in order to write clean, efficient, and extensible code.

Whether you are interviewing with leading technical companies or startups, practicing through these C++ interview questions and answers helps you perform better during coding rounds, systems design interviews, and practical debug scenarios.

FAQs on C++ Interview Questions and Answers

1. Which job roles require strong C++ skills in 2025?

C++ is necessary for roles like Software Developer, Game Developer, Embedded Systems Engineer, Quantitative Developer, and Systems Programmer. C++ is also being applied widely in high-frequency trading, AR/VR, and self-driving systems.

2. How is the C++ interview process structured at top companies?

All technical companies follow a multi-round interviewing procedure that includes:

• Online coding rounds (DSA + STL)
• Technical interviews (OOP, memory management, C++ features)
• Design of systems (for advanced jobs)
• Behavioral or HR round

3. Which companies frequently hire C++ developers?

Leading companies that hire C++ developers are:

• Google, Microsoft, Amazon, Meta
• NVIDIA, Bloomberg, Morgan Stanley
• Qualcomm, Samsung, Siemens
• Gaming technologies, robotics, and finance startups are also looking for professional C++ skills.

4. What salary can a C++ developer expect in 2025?

Salary is based on the job and experience:

• Entry-level C++ Developer: INR 8–12 LPA (India) or USD 90K– USD 120K 

• Mid-level (3–5 years): INR 15–25 LPA or USD 120K– USD150K

• Senior/Lead: INR 30+ LPA or USD 150K+

5. What is the future of C++ in Software Development?

C++ continues to be a root language in 2025 and later in high-performance systems, game programming, financial simulations, and embedded programs. With modern updates like C++20 and C++23, the programming language continues to evolve to hold its ground against new programming languages rising and also offer unmatched speed, low-level programming, and multi-platform support.