C++ Exception Handling Interview Questions and Answers for freshers

1. What is exception handling?

   • Answer: Exception handling is a mechanism to manage runtime errors in a program. It allows you to gracefully handle unexpected events without causing the program to crash.

2. What are the benefits of using exception handling?

   • Answer: Benefits include improved code robustness, better error management, separation of error-handling code from main logic, and easier debugging.

3. What are the keywords used in C++ exception handling?

   • Answer: `try`, `catch`, and `throw`.

4. Explain the `try`, `catch`, and `throw` keywords.

   • Answer: `try` block encloses code that might throw exceptions. `throw` throws an exception object. `catch` block handles the exception if one is thrown.

5. What is a `throw` expression?

   • Answer: A `throw` expression signals that an exception has occurred. It can throw any object that can be copied.

6. What is a `catch` block?

   • Answer: A `catch` block specifies the type of exception it can handle. It contains the code to handle the exception.

7. How does exception handling work in C++?

   • Answer: When an exception is thrown, the program searches for a matching `catch` block. If found, that block executes. If not, the program terminates (unless a global handler is defined).

8. What is the importance of exception specifications? (Deprecated in C++11)

   • Answer: Exception specifications (e.g., `void func() throw(int, double);`) declared which exceptions a function could throw. However, they are now considered harmful and deprecated in C++11 and later, as they don't prevent unexpected exceptions.

9. What happens if no matching `catch` block is found?

   • Answer: The program terminates abnormally (unless a global `catch(...)` block is present). This is usually accompanied by an error message.

10. What is the difference between `catch(const std::exception& e)` and `catch(...)`?

    • Answer: `catch(const std::exception& e)` catches exceptions derived from `std::exception`. `catch(...)` is a catch-all handler that catches any exception.

11. What is the order of execution of multiple `catch` blocks?

    • Answer: The `catch` blocks are checked in order of appearance. The first matching `catch` block is executed.

12. Can you throw an exception from within a `catch` block?

    • Answer: Yes, you can re-throw exceptions using `throw;` or throw a different exception.

13. Explain the concept of stack unwinding.

    • Answer: When an exception is thrown, the stack unwinds. Destructors of objects on the stack are called in reverse order of construction until a matching `catch` block is found.

14. What is a good practice for exception handling?

    • Answer: Handle exceptions at the appropriate level, avoid catching too broadly (`catch(...)`), provide informative error messages, and ensure resource cleanup (e.g., file closing) in destructors or `finally` (if using RAII).

15. How to handle exceptions from third-party libraries?

    • Answer: Consult the library's documentation for the types of exceptions it throws and handle them appropriately in your `catch` blocks.

16. What are custom exceptions? How do you define one?

    • Answer: Custom exceptions are user-defined exception classes derived from `std::exception` or other exception classes. They allow for more specific error handling.

17. Why should you avoid catching exceptions by value?

    • Answer: Catching by value may cause unnecessary object copying and potentially lead to performance issues, especially for large objects. Catching by reference (`const &`) is preferred.

18. What is the role of destructors in exception handling?

    • Answer: Destructors ensure that resources are released even if exceptions are thrown. They are crucial for RAII (Resource Acquisition Is Initialization).

19. Write a C++ program to demonstrate exception handling using a custom exception class.

    • Answer: [Code example demonstrating a custom exception class, `try`, `catch`, and `throw`]

20. Explain the concept of Resource Acquisition Is Initialization (RAII).

    • Answer: RAII is a programming idiom where resource management is tied to object lifetime. Resources are acquired in the constructor and released in the destructor, ensuring proper cleanup even in the face of exceptions.

21. What are some common exceptions in the Standard Template Library (STL)?

    • Answer: `std::out_of_range`, `std::invalid_argument`, `std::logic_error`, `std::runtime_error`.

22. How do you handle exceptions that might be thrown from within a function called by another function?

    • Answer: Propagate the exceptions using `try...catch` blocks in both the calling and called functions. The calling function can handle exceptions thrown from the called function, or it can re-throw them.

23. What is the difference between checked and unchecked exceptions? (Not directly in C++)

    • Answer: While C++ doesn't have a formal distinction like Java, the concept applies. Checked exceptions (conceptually) would force the programmer to handle them explicitly, while unchecked exceptions are runtime errors that may or may not be explicitly handled. C++ favors the unchecked approach.

24. What is the significance of `std::exception`?

    • Answer: It is the base class for many standard exceptions, providing a common interface and facilitating polymorphic exception handling.

25. Discuss the importance of logging in exception handling.

    • Answer: Logging provides a record of exceptions, including timestamps, error messages, and stack traces, which is invaluable for debugging and post-mortem analysis.

26. How can you improve the readability of your exception handling code?

    • Answer: Use meaningful variable names, provide informative error messages, structure your `try...catch` blocks logically, and avoid deeply nested exception handling.

27. Describe a scenario where exception handling is not appropriate.

    • Answer: Exception handling adds overhead. For simple, predictable errors that can be easily handled using conditional statements (e.g., invalid user input that can be easily checked before processing), exception handling might be overkill.

28. What are the potential performance implications of exception handling?

    • Answer: Throwing and catching exceptions has performance overhead due to stack unwinding and the function call overhead. Excessive exception handling can impact performance.

29. How to properly clean up resources in the presence of exceptions (beyond destructors)?

    • Answer: RAII is the primary method. If absolutely necessary, `std::unique_ptr` and `std::shared_ptr` offer safer resource management than raw pointers. `finally` blocks (not directly in C++ but achievable with RAII or other patterns) can ensure cleanup regardless of success or failure.

30. What is the difference between `std::exception` and `std::runtime_error`?

    • Answer: `std::runtime_error` is a derived class of `std::exception` specifically designed for runtime errors.

31. Explain the use of `std::terminate()`

    • Answer: `std::terminate()` is called when exception handling fails, typically due to a lack of a suitable `catch` block.

32. What are the best practices for choosing exception types?

    • Answer: Create custom exception classes for application-specific errors, use standard exception types for common errors, and avoid generic exceptions if possible.

33. How to effectively use exception handling for file I/O operations?

    • Answer: Use `std::fstream` with RAII to manage file handles, and catch exceptions like `std::ios_base::failure`.

34. Describe a situation where you might use a nested `try...catch` block.

    • Answer: Nested `try...catch` blocks are useful when dealing with multiple potential exceptions at different levels of code execution.

35. Explain exception safety guarantees (basic, strong, nothrow).

    • Answer: These describe the level of guarantee a function provides regarding resource management and data consistency if an exception is thrown. Basic guarantees that resources are released. Strong guarantee ensures both resource release and data consistency. Nothrow guarantees no exceptions will be thrown.

36. What is the purpose of `std::set_terminate`?

    • Answer: `std::set_terminate` allows you to register a custom function to be called when `std::terminate` is invoked.

37. What is the difference between exceptions and error codes?

    • Answer: Exceptions disrupt the normal flow of execution, while error codes require explicit checks. Exceptions are generally better for handling unexpected errors, while error codes suit expected errors or situations that require finer-grained control.

Thank you for reading our blog post on 'C++ Exception Handling Interview Questions and Answers for freshers'.We hope you found it informative and useful.Stay tuned for more insightful content!