Hey there!
Getting ready for a C++ interview can feel a bit like gearing up for a big adventure. There’s a lot to learn and remember, but don’t worry—I’m here to help you navigate through it all. In this blog post, I’ll walk you through some of the most common C++ interview questions and provide clear, straightforward answers. Think of it as your trusty guide to mastering those tricky concepts and showing off your skills in the interview.
1. What is C++?
C++ is a high-level, general-purpose programming language developed as an extension of the C programming language with object-oriented features. Its key features include strong type checking, rich library support, and the ability to create complex data structures and algorithms.
2. What is the concept of object-oriented programming?
Object-Oriented Programming (OOP) is a paradigm based on the concept of objects, which can contain data and methods. The four main principles of OOP are encapsulation, abstraction, inheritance, and polymorphism.
3. What is Encapsulation?
Encapsulation is the bundling of data and methods that operate on the data into a single unit (class). It restricts direct access to some object’s components and prevents accidental modification.
class Car {
private:
int speed;
public:
void setSpeed(int s) {
speed = s;
}
int getSpeed() {
return speed;
}
};
4. What do you mean by friend function?
In C++, a friend function is a function that is not a member of a class but is allowed to access the private and protected members of the class. It is declared by using the friend keyword inside the class whose private and protected members it needs to access.
Here,The ‘Library’ class with a private member ‘numBooks’. It uses a friend function, ‘checkBooks’ , to access and print the private ‘numBooks’ of a ‘Library’ object. In ‘main()’, it creates a ‘Library’ object and uses ‘checkBooks’ to display the number of books.
#include <iostream>
using namespace std;
class Library {
private:
int numBooks;
public:
// Const5699f0ructor to set the number of books
Library(int n) : numBooks(n) {}
// Declare checkBooks as a friend function
friend void checkBooks(Library lib); }
// Define the friend function
void checkBooks(Library lib) {
// Access the private member numBooks
cout << “The library has “ << lib.numBooks << ” books.” << endl;
}
int main() {
Library myLibrary(500); // Create a Library object with 500 books
// Call the friend function to check and print the number of books
checkBooks(myLibrary);
return 0;
}
5. What is a constructor in C++
An automatically executed member function whenever an object is created is called a constructor. It has the same name as the class it belongs to. Thus, the compiler knows that the member function is a constructor. No return type is used for constructors.
Constructor Types:
- Default Constructor
- Copy Constructor
- Private Constructor
- Parametarized Constructor
- Static Constructor
6. What are the different types of Polymorphism ?
Polymorphiosm means multiple forms. It means having more than one function with the same function name but with different functionalities. Polymorphism is of two types:
1) Runtime Polymorphism (Function Overriding)
Runtime polymorphism is also known as dynamic polymorphism. Function overriding is an example of runtime polymorphism. Function overriding means when the child class contains the method which is already present in the present class. Hence, the child class overrides the method of the present class. In case of function overriding, parent and child class both contains the same function with the different definition. The call to the function is determined at runtime is known as runtime polymorphism.
2) Compile time Polymorphism
Compile-time polymorphism is also known as static polymorphism. The polymorphism which is implemented at the compile time is known as compile-time polymorphism. Methods overloading is an example of compile-time polymorphism.
Method Overloading: Method overloading is a technique which allows you to have more than one function with the same function name but with different functionality.
Method overloading can be possible on the following basis:
- The return type of the overloaded function.
- The type of the parameters passed to the function.
- The number of the parameters passed to the function.
7. What is a destructor?
A Destructor is used to delete any extra resources allocated by the object. A destructor function is called automatically once the object goes out of the scope.
Rules of destructor:
- Destructors have the same name as the class name and it is preceded by a tilde.
- It does not contain any argument and no return type.
8. What is an object?
An object is a run-time entity. You can create number of object from single class. An object is the instance of the class. An object can represent a person, place or any other item. An object can operate on both data members and member function. The class does not occupy any memory space. When an object is created using a new keyword, Then space is allocated for the variable in a heap, and the starting address is stored in the stack memory. When an object is created without a new keyword, then space is not allocated in the heap memory, and the object contains the null value in the stack.
9. What is dynamic memory allocation in C++?
Dynamic memory allocation refers to the allocation of memory at runtime using operators like new (for objects) and malloc (for raw memory) .
10. Explain the concept of RAII (Resource Acquisition Is Initialization)
RAII is a C++ programming technique where the lifetime of a resource is tried to the scope of an objects. Resources are acquired in the constructor and released in the destructor.
11. What is a smart pointer?
Smart pointers are objects that act as pointers but provide automatic memory management. They automatically deallocate memory when it is no longer needed, preventing memory leaks.
12. What is the STL?
The Standard Template Library (STL) is a collection of template classes and functions in C++ that provides common data structures and algorithms for efficient programming. It helps to use and manage data efficiently by providing generic implementations of common operations.
13. Difference between vector and list inSTL
| Feature | 'vector' | 'list' |
|---|---|---|
|
Structure |
Dynamic array (continugous memory) |
Doubly linked list (nodes with pointers) |
|
Element Access |
Fast random access via index ('0(1)') |
No direct access; must traverse ('0(n)') |
|
Insertion/Deletion |
Efficient at the edge ('0(1)' average) |
Efficient anywhere ('0(1)' with interator) |
|
Performance |
Slower for insertions/deletions in the middle ('0(n)') |
Faster for insertions/deletions anywhere ('0(1)' with interator) |
|
Memory Overhead |
Low (just the element storage) |
Higher (additional memory for pointers) |
|
Resizing |
Automatically resizes: may cause overhead with frequent resizing |
No resizing; fixed size elements managed by pointers |
|
Iteration |
Fast interation with random access |
Efficient interation with bidirectional traversal |
|
Use Case |
Best for scenarios needing fast access and occasional end modifications |
Best for frequent insertions/removals at arbritary positions |
14. What is an interator?
An interactor is an object that allows interating over the elements of a container without exposing the underlying representation.
#include <iostream>
#include <vector>
int main() {
// Create a vector of integers
std::vector<int> numbers = {10, 20, 30, 40, 50};
// Declare an iterator for the vector
std::vector<int>::iterator it;
// Use the iterator to traverse and print each element
for (it = numbers.begin(); it != numbers.end(); ++it) {
std::cout << *it << ” “; // Dereference the iterator to get the value
}
std::cout << std::endl;
return 0;
}
15. What is Multi-threading in c++?
Multi-threading is the concurrent execution of two or more threads. Threads are lightweight processes that share the same resources but run independently.
16. What is the difference between shallow copy and deep copy?
Shallow copy creates a new object but does not duplicate the dynamic memory pointed to by the original object. Deep copy creates a new object and duplicates the dynamic memory as well.
17. What is operator overloading?
Operator overloading allows defining custom behaviours for operators like like ‘+’, ‘ -’, or ‘==’ when used with user-defined classes or data types.
18. Difference Between new and malloc() ?
| Aspects | 'new' | 'malloc' |
|---|---|---|
|
Type safety |
Tye-safe; returns a pointer of the appropriate type (e.g, 'init*', 'complex*') |
Not type-safe; returns a 'void*' that needs to be explicitly cast |
|
Constructor call |
Calls the constructor for object initialization |
Do not call constructors; only allocates row memory |
|
Array Allocation |
Can allocate arrays using 'new Type [n]' and calls constructors for each element |
Allocates row memory for arrays using 'malloc(sizeof (Type) * n)' without initialization |
|
Deallocation |
use 'delete' for single objects and 'delete[ ]' for arrays |
Use 'free' for both single objects and arrays |
|
Error Handling |
Throws 'std : : bad_alloc' exception on failure |
Returns 'NULL' on failure; requires manual checking |
|
Initialization |
Automatically initializes objects if a constructor is defined |
Requires manual initialization after allocation |
|
Usage in c++ |
Preferred in C++ for dynamic memory management and object creation |
Generally used in C (but can be used in C++ for row memory allocation) |
19. What is Scope resolution operator :: ?
The scope resolution operator (::) in C++ is used to specify which variable or function you mean when there might be multiple options.
- Accessing Global Variables: If you have a global variable and a local variable with the same name, you use :: to access the global one. For example, ::variable refers to the global variable.
- Defining Class Methods: When you define a method outside of a class, you use :: to show it belongs to that class. For example, ClassName::method().
- Namespaces: If you have multiple namespaces with functions or variables of the same name, :: helps you specify which namespace you’re referring to. For example, NamespaceName::function().
In essence, :: helps you be clear about which part of your code you’re talking about.
20. What is the typeid operator?
The typeid operator allows obtaining the type information of an object at runtime. It return a reference to a type_info object representing the object’s type.
21. What is ternary operator?
The ternary operator (?:) is a shorthand way of writing an if-else statement. It evaluates a condition and returns one of two values based on the result of the condition.
The ternary operator has the following syntax:
condition ? expression1 : expression2;
22. What is a lambda function?
A lambda function is an anonymous function that can capture variables from its enclosing scope. It provides a concise way to define short functions.
23. What is move semantics?
Move semantics allow transferring ownership of resources (like memory) from one object to another without making a copy. It improves performance by avoiding unnecessary deep copies.
24. Explain the use of the override and final keywords in C++.
> override: Used in a derived class to indicate that a virtual function is overriding a base class function. Helps to avoid errors due to function signature mismatches.
class Base {
public:
virtual void show() {}
};
class Derived : public Base {
public:
void show() override {}
};
> final: Prevents further overriding of a virtual function or inheritance from a class.
class Base {
public:
virtual void show() final {}
};
class Derived final : public Base {};
// class FurtherDerived : public Derived {}; // Error: Derived is marked as final
25. What are rvalue references and how do they differ from lvalue references?
> Lvalue References (‘T&’): Refer to an existing object that has a name and a persistent address.
> Rvalue References (‘T&&’): Refer to temporary objects (rvalues) that do not have a persistent address. They enable move semantics by allowing resources to be moved rather than copied.
26. How does the std::move function work and when should it be used?
‘std::move’ is used to indicate that an object can be moved rather than copied. It casts its argument to an rvalue reference, allowing the efficient transfer of resources from one object to another.
std::vector<int> vec1 = {1, 2, 3};
std::vector<int> vec2 = std::move(vec1); // Moves vec1’s data to vec2
After the move, vec1 is in a valid but unspecified state. Use std::move when you want to avoid the overhead of copying large objects and when you no longer need the original object.
27. Explain the concept of "copy elision" and when it occurs.
Copy elision is an optimization technique where the compiler eliminates unnecessary copying of objects, particularly in return statements and object initialization. It is allowed by the C++ standard and can improve performance by reducing the overhead of copying.
Situations where copy elision occurs:
> When a temporary object is returned from a function and used to initialize another object.
> During the initialization of an object using a temporary object.
Conclusion
Thanks for reading! Remember, practice makes perfect. Keep revisiting these questions, understand the underlying concepts, and try to apply them in real-world scenarios. The more comfortable you are with the material, the more naturally you’ll be able to respond during your interview. Ihope this guide has been helpful and that you feel more at ease with the interview process. Best of luck in your C++ interview—go out there and show them what you’ve got!
