C++ Interview Questions And Answers (Part-C)

Part-C of C++ interview questions along with their answers:

21. What is the difference between new and delete and malloc and free?

• new and delete are C++ operators used for dynamic memory allocation and deallocation, respectively. They call constructors and destructors for objects.
• malloc and free are C functions from C standard library used for dynamic memory allocation and deallocation, respectively. They do not call constructors and destructors, so not suitable for C++ objects.

22. What is the this pointer in C++?

• The this pointer is a special pointer available inside the member functions of a class. It points to the current object that the member function is being called on. It is used to access the members of the current object.

23. Explain the const correctness in C++.

• const correctness refers to the practice of using const properly to make sure that objects are not modified unintentionally. It involves using const with member functions that do not modify the object, and using const with parameters to prevent their modification within the function.

24. What is a virtual destructor? Why is it used?

• A virtual destructor is a destructor that is declared as virtual in the base class. When a derived class object is deleted through a pointer to the base class, a virtual destructor ensures that the correct destructor (including the derived class destructor) is called, preventing memory leaks.

25. How is function overloading different from function overriding?

• Function overloading allows multiple functions with the same name in the same class, but with different parameter lists.
• Function overriding occurs in a derived class when a virtual function in the base class is redefined with the same name and parameter list.

26. What are lambda expressions in C++?

• Lambda expressions are anonymous functions that can be defined inline. They provide a concise way of defining function objects (functors) on the fly, especially for short, one-off operations.

27. What are namespaces in C++?

• Namespaces are used to group related variables, functions, and classes together to avoid naming conflicts. They provide a way to organize code and improve code modularity.

28. Explain the concept of move semantics in C++11.

• Move semantics allow objects to be efficiently transferred (moved) from one location to another, rather than copied. It is particularly useful when dealing with expensive-to-copy objects like large containers or dynamically allocated memory.

29. What is the difference between std::map and std::unordered_map in the C++ STL?

• std::map is an ordered associative container that stores elements as key-value pairs in sorted order based on the keys.
• std::unordered_map is an unordered associative container that stores elements as key-value pairs without any specific order, providing faster lookup times.

30. What is the role of the explicit keyword in C++ constructors?

• The explicit keyword is used to prevent implicit conversions in constructors. When a constructor is marked as explicit, it cannot be used for implicit type conversions.