C++ Interview Questions & Answers

C++ Basics:

1. What is C++?

   • Answer: C++ is a general-purpose programming language that is an extension of the C programming language. It includes object-oriented features and supports low-level memory manipulation.

2. Differentiate between C and C++.

   • Answer: C++ includes features like classes, objects, and inheritance, making it an object-oriented programming language, whereas C is procedural.

3. Explain the concept of Object-Oriented Programming (OOP).

   • Answer: OOP is a programming paradigm that uses objects (instances of classes) to structure and organize code. It involves concepts like encapsulation, inheritance, and polymorphism.

4. What is a class in C++?

   • Answer: A class is a user-defined data type in C++ that defines a blueprint for objects. It encapsulates data and functions that operate on that data.

5. What is an object in C++?

   • Answer: An object is an instance of a class in C++. It represents a real-world entity and encapsulates data and behavior.

Pointers and Memory Management:

6. What is a pointer in C++?

   • Answer: A pointer is a variable that stores the memory address of another variable. It allows direct manipulation of memory.

7. Explain the difference between new and malloc in C++.

   • Answer: new is an operator in C++ used for dynamic memory allocation with built-in type support, while malloc is a function in C for dynamic memory allocation.

8. What is the purpose of the delete operator in C++?

   • Answer: The delete operator is used to deallocate memory that was allocated using the new operator.

9. What is a reference in C++?

   • Answer: A reference is an alias for a variable. It provides an alternative name for an existing variable.

10. Explain the concept of const pointers and pointer to const in C++.

    • Answer: A const pointer is a pointer whose value (memory address) cannot be changed, and a pointer to const is a pointer that points to a const variable, preventing modification of the variable through the pointer.

Functions and Overloading:

11. What is function overloading in C++?

    • Answer: Function overloading is the ability to define multiple functions with the same name but different parameter lists in a C++ program.

12. Explain the difference between pass by value and pass by reference in C++.

    • Answer: Pass by value involves passing the actual value of a variable to a function, while pass by reference involves passing the memory address of the variable.

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

    • Answer: A default argument is a parameter in a function that has a default value. If a value is not provided when the function is called, the default value is used.

14. What is a function template in C++?

    • Answer: A function template is a way to create a generic function that can work with different data types without rewriting the code for each type.

15. Explain the purpose of the inline keyword in C++.

    • Answer: The inline keyword is a suggestion to the compiler to replace a function call with the actual code of the function to improve performance.

Object-Oriented Concepts:

16. What is encapsulation in C++?

    • Answer: Encapsulation is the bundling of data and methods that operate on the data within a single unit, often a class in C++.

17. Explain the concept of inheritance in C++.

    • Answer: Inheritance is a mechanism in C++ that allows a class (derived or child class) to inherit properties and behaviors from another class (base or parent class).

18. What is polymorphism in C++?

    • Answer: Polymorphism allows objects of different types to be treated as objects of a common type. In C++, polymorphism is achieved through function overloading and virtual functions.

19. What are virtual functions in C++?

    • Answer: Virtual functions in C++ are functions declared in a base class that can be overridden in derived classes. They enable dynamic polymorphism.

20. Differentiate between early binding and late binding in C++.

    • Answer: Early binding (static binding) occurs at compile time, while late binding (dynamic binding) occurs at runtime. Virtual functions enable late binding.

Templates and Generic Programming:

21. What is a template in C++?

    • Answer: A template in C++ allows the creation of generic classes and functions that can work with different data types.

22. Explain the purpose of the typename keyword in C++ templates.

    • Answer: The typename keyword is used in template programming to indicate that a dependent name should be treated as a type.

23. What is specialization in C++ templates?

    • Answer: Template specialization in C++ allows the definition of different implementations for a template based on the specific type.

24. How are function templates different from class templates in C++?

    • Answer: Function templates define generic functions, while class templates define generic classes. Both allow the use of different data types.

25. What is the purpose of the STL in C++?

    • Answer: The Standard Template Library (STL) in C++ provides a set of generic classes and functions with templates to implement common data structures and algorithms.

Standard Template Library (STL):

26. Explain the purpose of the vector container in the STL.

    • Answer: The vector container in the STL is a dynamic array that provides dynamic resizing and supports random access to elements.

27. What is an iterator in C++ STL?

    • Answer: An iterator in C++ STL is an object that allows the traversal of elements in a container. It acts as a pointer to elements.

28. What is the difference between list and vector in C++ STL?

    • Answer: vector is a dynamic array with random access, while list is a doubly-linked list with sequential access. list allows efficient insertion and deletion in the middle.

29. Explain the purpose of the map container in C++ STL.

    • Answer: The map container in C++ STL is an associative container that stores key-value pairs. It provides fast lookup and insertion based on the keys.

30. What is the purpose of the algorithm header in C++ STL?

    • Answer: The algorithm header in C++ STL provides a collection of functions for working with sequences, such as searching, sorting, and manipulating elements.

Exception Handling:

31. What is exception handling in C++?

    • Answer: Exception handling in C++ is a mechanism to handle runtime errors gracefully. It involves the use of try, catch, and throw keywords.

32. **Explain the purpose of the `try

, catch, and finallyblocks in C++ exception handling.** - **Answer:** Thetryblock contains the code that might throw an exception. Thecatchblock handles the exception, and thefinally` block (not in C++, but in some languages) contains code that is executed regardless of whether an exception is thrown.

33. What is the std::exception class in C++?

    • Answer: std::exception is the base class for all standard C++ exceptions. It provides a what() method to retrieve an exception description.

34. Explain the difference between stack unwinding and exception propagation.

    • Answer: Stack unwinding is the process of deallocating local variables when an exception is thrown, while exception propagation is the transfer of control to the nearest catch block.

35. How do you create a custom exception class in C++?

    • Answer: A custom exception class in C++ is created by inheriting from std::exception and providing a custom implementation.

File Handling:

36. What is file handling in C++?

    • Answer: File handling in C++ involves reading from and writing to files. It uses the fstream library.

37. Explain the difference between text mode and binary mode in file handling.

    • Answer: Text mode reads and writes data as text, with newline conversions. Binary mode reads and writes data as-is, without any conversion.

38. What is the purpose of the ifstream and ofstream classes in C++ file handling?

    • Answer: ifstream is used for reading from a file, and ofstream is used for writing to a file.

39. How do you check if a file exists in C++?

    • Answer: File existence in C++ can be checked using the ifstream constructor, which returns true if the file exists.

40. Explain the concept of file positioning in C++.

    • Answer: File positioning in C++ involves moving the file pointer to a specific location within the file using functions like seekg and seekp.

Miscellaneous:

41. What is a smart pointer in C++?

    • Answer: Smart pointers in C++ are objects that act like pointers but provide automatic memory management. Examples include std::unique_ptr and std::shared_ptr.

42. Explain the purpose of the const keyword in C++.

    • Answer: The const keyword in C++ is used to declare constants, indicate that a variable should not be modified, or specify that a member function does not modify the object.

43. What is the purpose of the volatile keyword in C++?

    • Answer: The volatile keyword in C++ is used to indicate that a variable may be changed by an external entity and should not be optimized by the compiler.

44. What is a lambda expression in C++?

    • Answer: A lambda expression in C++ is an anonymous function that can capture variables from its surrounding scope. It provides a concise way to define functions inline.

45. Explain the concept of multiple inheritance in C++.

    • Answer: Multiple inheritance in C++ involves a class inheriting from more than one base class. It introduces challenges like the diamond problem, where a derived class inherits from two classes that share a common base class.

46. What is the purpose of the typeid operator in C++?

    • Answer: The typeid operator in C++ is used to obtain information about the type of an expression. It is often used with polymorphic types.

47. Explain the purpose of the const_cast operator in C++.

    • Answer: The const_cast operator in C++ is used to add or remove the const qualifier from a variable. It is primarily used for casting away the const-ness.

48. What is a template specialization in C++?

    • Answer: Template specialization in C++ allows the definition of different implementations for a template based on the specific type.

49. Explain the concept of the preprocessor in C++.

    • Answer: The preprocessor in C++ is a tool that runs before the compilation process. It performs tasks like file inclusion, macro substitution, and conditional compilation.

50. What is the purpose of the explicit keyword in C++?

    • Answer: The explicit keyword in C++ is used to specify that a constructor or conversion function should not be implicitly called. It prevents implicit type conversions.