Top C++ Exception Handling Interview Questions and Answers for freshers

1. What is exception handling in C++?

   • Answer: Exception handling is a mechanism in C++ that allows you to gracefully handle runtime errors (exceptions) without causing your program to crash. It separates error-handling code from the main program logic, improving code readability and maintainability.

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

   • Answer: The main keywords are `try`, `catch`, and `throw`. `try` blocks enclose code that might throw exceptions. `throw` throws an exception. `catch` blocks handle exceptions of specific types.

3. Explain the `try-catch` block.

   • Answer: A `try` block contains code that might generate an exception. If an exception is thrown within the `try` block, the program searches for a matching `catch` block. The `catch` block specifies the exception type it can handle and contains code to recover from the error.

4. What is the purpose of the `throw` keyword?

   • Answer: The `throw` keyword explicitly signals an exception. It can throw a value of any type, often a custom exception class.

5. What is a catch-all handler?

   • Answer: A catch-all handler is a `catch(...)` block that catches any type of exception. It's generally used as a last resort to prevent the program from terminating unexpectedly, but it should be used sparingly as it can mask errors.

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

   • Answer: If no matching `catch` block is found for a thrown exception, the program terminates abnormally, often printing an error message to the console (unless handled by a higher level mechanism).

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

   • Answer: You create a custom exception class by deriving it from a standard exception class like `std::exception` or `std::runtime_error`. This allows you to define specific exception types and associated data.

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

   • Answer: `std::exception` is a base class for all standard exceptions. `std::runtime_error` is a derived class specifically for runtime errors, offering a `what()` method to get an error message string.

9. What is the `what()` method in exception classes?

   • Answer: The `what()` method (often inherited from `std::exception` or `std::runtime_error`) returns a `const char*` representing a descriptive message about the exception.

10. Explain exception specifications (deprecated).

    • Answer: Exception specifications, using `throw()`, were used to declare which exceptions a function could throw. However, they are deprecated in modern C++ as they often hinder exception safety and are generally considered bad practice.

11. What is RAII (Resource Acquisition Is Initialization)? How does it relate to exception handling?

    • Answer: RAII is a programming idiom where resources (like files, memory, locks) are managed by objects with destructors. When an exception occurs, destructors are automatically called, ensuring resources are released even if exceptions are thrown, preventing resource leaks.

12. Explain the importance of exception safety.

    • Answer: Exception safety guarantees that resources are properly managed and the program's state remains consistent even if exceptions occur. It prevents data corruption, memory leaks, and other issues.

13. What are the different levels of exception safety?

    • Answer: Basic guarantee: Resources are released. Strong guarantee: The program's state remains consistent (no partial changes). Nothrow guarantee: No exceptions are thrown.

14. How can you handle exceptions in constructors?

    • Answer: If an exception is thrown in a constructor, the destructor of partially constructed objects is *not* called. Therefore, careful resource management (RAII) is crucial to avoid resource leaks. Throw exceptions early in constructors.

15. How can you handle exceptions in destructors?

    • Answer: Destructors should generally avoid throwing exceptions. If an exception is thrown in a destructor, it can lead to undefined behavior, especially when already handling another exception. Log the error instead.

16. What is a stack unwinding?

    • Answer: Stack unwinding is the process of deallocating stack frames when an exception is thrown. Destructors of objects on the stack are called during unwinding to release resources.

17. Should you use exceptions for normal program flow control?

    • Answer: No. Exceptions are for handling exceptional conditions, not normal program flow. Using exceptions for regular control flow makes the code harder to read and debug.

18. What are some best practices for exception handling?

    • Answer: Use specific catch blocks, avoid catch-all handlers unless absolutely necessary. Handle exceptions at the appropriate level. Don't let exceptions go unhandled. Use RAII for resource management. Log exceptions appropriately.

19. How can you use exceptions to improve code readability?

    • Answer: By separating error handling from the main logic, exceptions enhance readability. Error handling code is localized to catch blocks, keeping the main code cleaner.

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