c engineer Interview Questions and Answers

1. What is the difference between `malloc` and `new`?

   • Answer: `malloc` allocates raw memory and returns a void pointer. It doesn't call constructors. `new` allocates memory and calls the constructor of the object being created. `new` also handles potential exceptions. `free` is used to deallocate memory allocated by `malloc`, while `delete` deallocates memory allocated by `new` and calls the destructor.

2. Explain the concept of polymorphism in C++.

   • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. It's achieved through virtual functions and inheritance. A virtual function allows derived classes to provide their own implementations of a base class function, determined at runtime.

3. What are virtual functions and why are they important?

   • Answer: Virtual functions are member functions declared with the `virtual` keyword in the base class. They enable runtime polymorphism. When a virtual function is called through a pointer or reference to a base class object, the correct version of the function (from the derived class) is executed, regardless of the object's declared type. This is crucial for dynamic dispatch and flexibility in object-oriented programming.

4. What is the difference between a class and a struct in C++?

   • Answer: The primary difference is the default access specifier: `class` members are private by default, while `struct` members are public by default. Functionally, they are otherwise identical.

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

   • Answer: Inheritance allows a class (derived class or subclass) to inherit properties and behaviors from another class (base class or superclass). It promotes code reusability and establishes an "is-a" relationship between classes. Different types of inheritance include single, multiple, multilevel, and hierarchical inheritance.

6. What are smart pointers and why are they used?

   • Answer: Smart pointers (e.g., `unique_ptr`, `shared_ptr`, `weak_ptr`) are classes that act like pointers but automatically manage memory, preventing memory leaks. `unique_ptr` provides exclusive ownership, `shared_ptr` allows shared ownership, and `weak_ptr` provides a non-owning reference to an object managed by a `shared_ptr`.

7. What is the difference between `const` and `constexpr`?

   • Answer: `const` indicates that a variable's value cannot be changed after initialization. `constexpr` indicates that a variable's value can be computed at compile time and is a constant expression. A `constexpr` variable is implicitly `const`.

8. Explain operator overloading in C++.

   • Answer: Operator overloading allows you to redefine the behavior of operators (e.g., +, -, *, /) for user-defined types. This makes code using custom classes more intuitive and readable by allowing operators to work with objects in a familiar way.

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

   • Answer: A lambda expression is an unnamed function that can be defined inline. It's often used for short, concise functions passed as arguments to algorithms or used with higher-order functions.

10. What is RAII (Resource Acquisition Is Initialization)?

    • Answer: RAII is a programming idiom where resource allocation is tied to object creation, and resource deallocation is tied to object destruction. Smart pointers are a prime example of RAII; they ensure resources are automatically released when they go out of scope.

11. Explain the difference between a stack and a heap.

    • Answer: The stack is a LIFO (Last-In, First-Out) data structure that automatically manages memory allocation and deallocation. The heap is a region of memory where memory is dynamically allocated and deallocated using `new` and `delete` (or `malloc` and `free`). Stack memory is faster to access but has limited size, while heap memory is slower but can accommodate larger allocations.

12. What is a template in C++?

    • Answer: Templates allow you to write generic code that can work with different data types without being rewritten for each type. They enable compile-time polymorphism, improving code efficiency and reusability.

13. What is the Standard Template Library (STL)?

    • Answer: The STL is a powerful set of container classes (like `vector`, `list`, `map`), algorithms (like `sort`, `find`), and iterators that are part of the C++ standard library. It provides efficient and ready-to-use data structures and algorithms.

14. Explain exception handling in C++.

    • Answer: Exception handling uses `try`, `catch`, and `throw` keywords to handle runtime errors gracefully. A `try` block contains code that might throw an exception. `catch` blocks handle specific exception types. `throw` throws an exception object.

15. What is move semantics?

    • Answer: Move semantics allows efficient transfer of ownership of resources (like dynamically allocated memory) from one object to another without copying the data. It uses rvalue references (`&&`) to indicate that an object can be moved from.

16. What is perfect forwarding?

    • Answer: Perfect forwarding is a technique that allows you to forward function arguments to another function without losing information about whether the arguments are lvalues or rvalues. It's often used in conjunction with templates and move semantics to maximize efficiency.

17. Explain the role of the Standard Template Library (STL) iterators.

    • Answer: Iterators act as pointers for containers in STL, providing a way to traverse through elements. They abstract away the details of how a container stores data, enabling algorithms to work with various containers using the same interface.

18. Describe the difference between a vector and a list in the STL.

    • Answer: `vector` is a dynamic array providing efficient random access but slower insertions and deletions in the middle. `list` is a doubly-linked list offering fast insertions and deletions but slower random access. The choice depends on the application's access patterns.

19. What are the different types of iterators in the STL?

    • Answer: Common iterator categories include input iterators, output iterators, forward iterators, bidirectional iterators, and random access iterators. Each category defines the operations that can be performed on the iterator.

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