Top C++ Interview Questions and Answers
Preparing for a C++ interview requires a solid grasp of key concepts and common questions. Here are Top 40 C++ Interview Questions With Detailed Answers to help you succeed. First, understand the difference between C++ and other programming languages. C++ is a statically typed, compiled language with object-oriented features, offering better control over system resources and memory management compared to languages like Python or Java.
Another common question is about pointers in C++: Pointers are variables that store the address of another variable, enabling efficient array manipulation and dynamic memory allocation. Mastering these questions will boost your confidence and readiness for your C++ interview. This guide highlights essential react c++ interview questions to help you confidently showcase your expertise and land your desired role.
Basic C++ Interview Questions
Q.1 What is C++ and how does it differ from C?
C++ is a general-purpose programming language that extends the C programming language with object-oriented features. It differs from C mainly because it supports classes, inheritance, polymorphism, encapsulation, and other object-oriented principles, whereas C is procedural.
Q.2 What are the basic data types in C++?
The basic data types in C++ include integers (int), floating-point numbers (float, double), characters (char), and Boolean (bool).
Q.3 What is a namespace in C++ and why is it used?
A namespace in C++ provides a way to group a set of related symbols (such as functions, classes, variables) under a name to prevent name conflicts. It is used to avoid collisions and to organize code logically, for example, the std namespace in the Standard Library.
Q.4 What are the principles of Object-Oriented Programming?
The principles of Object-Oriented Programming (OOP) include encapsulation, which involves bundling the data and methods that operate on the data into a single unit or class; inheritance, which allows a class to inherit characteristics from another class; polymorphism, which allows methods to do different things based on the object it is acting upon; and abstraction, which reduces complexity by hiding unnecessary details in classes and interfaces.
Q.5 What is a pointer and how do you use it in C++?
A pointer in C++ is a variable that stores the memory address of another variable. Pointers are used for dynamic memory allocation, accessing arrays and functions, and by-reference parameter passing. You declare a pointer using the asterisk (*) symbol, and you can manipulate the memory address it points to using pointer arithmetic.
Q.6 Explain the structure of a C++ program.
The structure of a C++ program typically includes a set of header file inclusions, the main function definition, and other function definitions. The program execution starts from the main() function. The header files contain declarations of functions and classes used in the program, and the source file (.cpp) contains the actual definitions of these functions.
Q.7 What is a function in C++? Give an example.
A function in C++ is a group of statements that together perform a task. Every C++ program has at least one function, which is main(), and all the most trivial programs can define additional functions. For example:
int add(int a, int b) {
return a + b;
}
Q.8 How do you declare a variable in C++?
To declare a variable in C++, you must specify the type followed by the variable name, like so:
int age;
double weight;
Q.9 What is recursion in C++?
Recursion in C++ is the process of a function calling itself directly or indirectly, which enables the function to repeat its behavior until a base condition is met. It is commonly used for tasks that can be broken down into subtasks of the same form, such as calculating factorials.
Q.10 What are arrays in C++? How are they different from lists?
Arrays in C++ are collections of elements of the same type stored in contiguous memory locations. They differ from lists, which are part of the Standard Template Library (STL) in C++ and provide dynamic sizing, whereas arrays have a fixed size determined at compile time.
Q.11 What is the purpose of the main() function in C++?
The main() function in C++ serves as the entry point for program execution. It must be present in every C++ program. Execution of all C++ programs starts with the main() function, regardless of where the program is actually located within the source code.
Q.12 What are header files and what are the common C++ headers?
Header files in C++ contain declarations of functions and classes that are implemented in source files. Common C++ header files include for input/output operations, for using vector containers, for string manipulations, and for associative arrays.
Q.13 Explain the use of new and delete in C++.
new and delete are operators in C++ used for dynamic memory management. new is used to allocate memory on the heap for a variable or an array during runtime, and delete is used to free that memory to prevent memory leaks. For example:
int* ptr = new int; // allocates memory for an integer
delete ptr; // frees the allocated memory
Q.14 What is operator overloading?
Operator overloading in C++ allows operators to be redefined and used in different ways, depending on their operands. This enables operators to perform differently for objects than they do for standard data types. For example, you can redefine the + operator to concatenate two objects of a custom class.
Q.15 What are default arguments in functions?
Default arguments in functions are those that take a default value if no argument value is passed to them during the function call. This feature allows functions to be called with fewer arguments than are formally declared. For example:
void display(int a, int b = 10) {
std::cout << "a: " << a << ", b: " << b << std::endl;
}
Intermediate C++ Interview Questions
Q.16 What is a class in C++? Explain with an example.
A class in C++ is a blueprint for creating objects that encapsulate data and operations on data. It defines a type representing a concept or thing, complete with attributes and behaviors. For example:
class Car {
public:
string color;
int year;
void drive() {
cout << "Driving a " << color << " car from " << year << endl;
}
};
Q.17 What are virtual functions in C++?
Virtual functions in C++ are member functions that you expect to override in derived classes. When you use a virtual function, C++ creates a dynamic dispatch that allows the program to decide which function to use at runtime. They are used to achieve polymorphism.
Q.18 What is inheritance and how is it implemented in C++?
Inheritance is a feature of C++ that allows creating a new class (derived class) based on an existing class (base class). The derived class inherits the properties and behaviors of the base class, allowing for code reuse and the creation of a hierarchical classification. It is implemented using the colon syntax:
class Vehicle {
public:
string type;
};
class Car : public Vehicle {
public:
string model;
};
Q.19 Explain the concept of polymorphism in C++.
Polymorphism in C++ allows methods to do different things based on the object it is acting upon. It supports the ability of different classes to provide different implementations of the same interface or method. This can be achieved through virtual functions, which let the program decide the function to call at runtime based on the object.
Q.20 What are templates in C++?
Templates in C++ are a feature that allows functions and classes to operate with generic types. This means you can create a function or class to work with any data type without repeating the entire code for each type. For example, you can create a template for a function that adds two elements:
template <typename T>
T add(T a, T b) {
return a + b;
}
Q.21 What is exception handling and how does it work in C++?
Exception handling in C++ involves managing unexpected problems that arise during runtime. It is done using try, catch, and throw statements. try blocks contain code that might throw exceptions, catch blocks handle those exceptions, and throw is used to throw exceptions.
try {
// Code that may throw an exception
} catch (exceptionType1 &e) {
// Code to handle the exception
} catch (exceptionType2 &e) {
// Code to handle another type of exception
}
Q.22 What are the different types of inheritance in C++?
C++ supports several types of inheritance, including:
- Single inheritance: A class is derived from one base class.
- Multiple inheritance: A class can be derived from more than one base class.
- Multilevel inheritance: A class is derived from a derived class.
- Hierarchical inheritance: Multiple classes are derived from a single base class.
- Hybrid inheritance: A combination of more than one type of inheritance.
Q.23 What is the Standard Template Library (STL)?
The Standard Template Library (STL) is a powerful set of C++ template classes to provide general-purpose classes and functions with templates that implement many popular and commonly used algorithms and data structures like vectors, lists, queues, and stacks.
Q.24 How does malloc() differ from new?
malloc() is a C standard library function that allocates a specified amount of memory and returns a pointer to it, which is not type-safe and does not call constructors. new, on the other hand, is a C++ operator that allocates memory, returns a type-safe pointer, and calls the object’s constructor.
Q.25 What is a copy constructor and when should it be used?
A copy constructor in C++ is a constructor that initializes an object using another object of the same class. It is used when an object is created by copying another object, for example, when passing objects by value to a function.
class Car {
public:
string model;
Car(const Car &c) { // Copy constructor
model = c.model;
}
};
Q.26 Explain the difference between struct and class in C++.
The primary difference between struct and class in C++ is the default access level. struct defaults to public access for its members and base classes, while class defaults to private. This affects encapsulation but not the capabilities since both can have methods and attributes.
Q.27 What is the use of dynamic_cast?
dynamic_cast is used for safe downcasting at runtime. It converts a base pointer or reference to a derived pointer or reference, and it returns nullptr or throws an exception if the cast fails, making it useful for handling polymorphism safely.
Q.28 How can you prevent a class from being inherited?
In C++, you can prevent a class from being inherited by declaring it as final. This keyword, when used in the class declaration, stops other classes from inheriting from it.
class Base final {
// class definitions
};
Q.29 What are access specifiers? Give examples.
Access specifiers in C++ control the visibility of class members. The three types are:
public: Members are accessible from outside the class.private: Members cannot be accessed (or viewed) from outside the class.protected: Members cannot be accessed from outside the class, except by derived classes.
class MyClass {
public:
int publicVar;
private:
int privateVar;
protected:
int protectedVar;
};
Q.30 What is this pointer?
this is a special pointer in C++ that points to the object for which a member function is being executed. It is used to refer to the invoking object inside member functions.
Q.31 What is a pure virtual function?
A pure virtual function is a function that has no implementation in the base class and must be overridden in any derived class. Declaring at least one pure virtual function makes a class abstract, meaning it cannot be instantiated on its own.
class Base {
public:
virtual void show() = 0; // Pure virtual function
};
Q.32 How do you handle memory leaks in C++?
Memory leaks in C++ can be managed by ensuring that every dynamically allocated resource is properly deallocated. This involves using delete for memory allocated with new, and delete[] for arrays allocated with new[]. Tools like Valgrind or static analysis tools can also help identify leaks.
Q.33 Explain the use of const keyword.
The const keyword in C++ signifies that a variable’s value cannot be changed after initialization, making it constant. It can be used with variables, pointers, functions, and class methods to make them immutable or to prevent modification of the data they point to or represent.
Q.34 What is the difference between #include and #include “filename”?
In C++, #include is used for including system header files, which are looked up in standard system directories. include “filename” is used for including programmer-defined header files, which are looked up in the project’s directory first, then in the standard system directories.
Q.35 Explain the concept of namespaces in detail.
namespace myNamespace {
int myFunction() {
return 0;
}
}
// Using the namespace
using namespace myNamespace;
int x = myFunction();
Advanced C++ Interview Questions
Q.36 What are rvalue references and why are they used?
Rvalue references in C++ are used to implement move semantics and perfect forwarding. They bind to rvalues (temporary objects), allowing the reuse of their resources, thereby optimizing the performance especially during the copying of large objects. An rvalue reference is denoted by &&. This feature reduces unnecessary copying, which is particularly useful for objects that manage dynamic memory or other resources.
std::vector<int> createVector() {
return std::vector<int>{1, 2, 3};
}
std::vector<int> vec = createVector(); // The vector's resources are moved, not copied
Q.37 Explain the rule of three with examples.
The rule of three in C++ states that if a class defines one (or more) of the following it should probably explicitly define all three: destructor, copy constructor, and copy assignment operator. This rule is important for classes that manage resources like dynamic memory, file handles, etc., to ensure proper resource management.
class Resource {
int* data;
public:
Resource() {
data = new int[100]; // Allocate resource
}
~Resource() {
delete[] data; // Destructor to release resource
}
Resource(const Resource& other) { // Copy constructor
data = new int[100];
std::copy(other.data, other.data + 100, data);
}
Resource& operator=(const Resource& other) { // Copy assignment operator
if (this != &other) {
delete[] data;
data = new int[100];
std::copy(other.data, other.data + 100, data);
}
return *this;
}
};
Q.38 What is a lambda expression and how is it used in C++?
Lambda expressions in C++ allow the creation of anonymous function objects for short snippets of code that can be defined inline. They are useful for defining callback functions, for use with algorithms, or for encapsulating complex logic succinctly. A lambda expression has the form [capture](parameters) -> return_type { body }.
std::vector<int> v = {1, 2, 3, 4, 5};
std::for_each(v.begin(), v.end(), [](int x) { std::cout << x << " "; });
Q.39 Discuss the use of smart pointers in C++.
Smart pointers in C++ are template classes in the Standard Template Library (STL) that manage the lifetime of dynamically allocated objects. They ensure automatic deallocation of memory when the pointer (or last pointer in the case of shared_ptr) that owns the object goes out of scope. The three main types of smart pointers are:
unique_ptr: Owns an object exclusively and cannot be copied, only moved.shared_ptr: Manages the object through reference counting allowing multiple pointers to the same object.weak_ptr: Holds a non-owning reference to an object that is managed by ashared_ptr. Smart pointers are used to prevent memory leaks and are essential for resource management in modern C++ applications.
std::unique_ptr<int> p1(new int(5)); // `unique_ptr` owning an int
std::shared_ptr<int> p2(new int(10)); // `shared_ptr` owning another int
Q.40 How does the C++11 memory model enhance multithreaded programming?
The C++11 memory model provides a formal specification for how operations in different threads interact through memory and introduces atomic operations that are necessary for safely managing data in a multi-threaded environment. This model defines how memory is accessed and manipulated concurrently without invoking data races or undefined behavior. It also includes support for various mutex classes, condition variables, and thread-local storage, which enhance the safety and efficiency of concurrent applications. Atomic operations and proper synchronization primitives help in writing robust multithreaded C++ applications by ensuring that operations are performed without interference and memory effects are well-defined.
#include <atomic>
std::atomic<int> counter = {0};
void increment() {
counter.fetch_add(1, std::memory_order_relaxed); // Atomically increments counter
}
