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

1. What is exception handling? Why is it crucial in C++?

   • Answer: Exception handling is a mechanism to handle runtime errors gracefully, preventing program crashes. It separates error-handling code from the main logic, improving readability and maintainability. In C++, it's crucial for building robust and reliable applications that can recover from unexpected situations like invalid input, file I/O errors, or network issues.

2. Explain the `try`, `catch`, and `throw` keywords in C++.

   • Answer: `try` block encloses code that might throw an exception. `throw` keyword signals an exception, specifying the exception object. `catch` block handles exceptions thrown within the corresponding `try` block. Multiple `catch` blocks can handle different exception types.

3. What are the different types of exceptions in C++?

   • Answer: C++ supports both standard exceptions (like `std::exception`, `std::runtime_error`, `std::logic_error`) and custom exceptions. Standard exceptions provide a common base for various runtime errors. Custom exceptions allow developers to define specific exception types for their application's needs.

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

   • Answer: Create a class that inherits publicly from `std::exception` or one of its derived classes. Override the `what()` method to provide a descriptive error message. For example: `class MyException : public std::exception { public: const char* what() const throw() { return "My custom exception"; } };`

5. What is the difference between `catch(...)` and specific `catch` blocks?

   • Answer: `catch(...)` is a catch-all handler that catches any exception. Specific `catch` blocks handle specific exception types. While `catch(...)` is convenient, it can mask errors if not used carefully. Specific `catch` blocks provide better error handling and debugging.

6. Explain exception specifications in C++. Are they still recommended?

   • Answer: Exception specifications declare the types of exceptions a function can throw. However, they are largely deprecated in modern C++ because they can lead to unexpected behavior and are difficult to enforce reliably. It's better to rely on good coding practices and documentation.

7. What is the stack unwinding process during exception handling?

   • Answer: When an exception is thrown, the stack unwinding process occurs. The runtime environment automatically deallocates objects on the stack, calling destructors as it goes back up the call stack until a matching `catch` block is found. This ensures proper resource cleanup.

8. How to handle exceptions in constructors and destructors?

   • Answer: In constructors, if an exception is thrown before the object is fully initialized, the destructor is not called. In destructors, exceptions should be avoided as much as possible because there is no guarantee of proper recovery. Using RAII (Resource Acquisition Is Initialization) helps manage resources.

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

   • Answer: RAII is a C++ programming idiom where resource management is tied to the object's lifetime. Resources are acquired in the constructor and released in the destructor. This guarantees resource cleanup even if exceptions occur, making the code more robust.

10. Discuss the use of `std::exception_ptr` and `std::rethrow_exception`.

    • Answer: `std::exception_ptr` allows you to store and rethrow exceptions later, particularly useful for handling exceptions across function boundaries or asynchronous operations. `std::rethrow_exception` rethrows the stored exception.

11. Question 91: Explain the importance of logging in exception handling.

    • Answer: Logging exceptions provides valuable information for debugging and monitoring. It helps track errors, identify their causes, and monitor the system's health.

12. Question 92: How can you handle exceptions across threads?

    • Answer: Techniques like using futures and promises, or custom synchronization mechanisms, can help manage exceptions thrown in separate threads, ensuring that the main thread is informed and can handle the error appropriately.

13. Question 93: Describe best practices for exception handling in large projects.

    • Answer: Consistent exception handling style, clear error messages, centralized logging, appropriate exception granularity, and using custom exceptions are important for maintainability in large projects.

14. Question 94: What is the difference between checked and unchecked exceptions? (Relate to C++'s approach)

    • Answer: C++ doesn't have a formal distinction between checked and unchecked exceptions like some languages (Java). However, the concept applies: logic errors are often better handled within the function itself, while runtime errors are passed up using exceptions.

15. Question 95: Explain exception safety guarantees (basic, strong, nothrow).

    • Answer: Basic exception safety guarantees that no resources are leaked if an exception is thrown. Strong exception safety guarantees that the program remains in a valid state. Nothrow guarantees that no exceptions will be thrown.

16. Question 96: How can you test exception handling effectively?

    • Answer: Unit testing frameworks can be used to simulate exceptions and verify that the `catch` blocks handle them appropriately and that the program's state remains valid.

17. Question 97: What are some common pitfalls to avoid when using exceptions?

    • Answer: Overuse of exceptions, neglecting resource cleanup, poor exception message design, ignoring exceptions, and overly broad `catch(...)` blocks are common pitfalls.

18. Question 98: How can you use exceptions to improve code readability and maintainability?

    • Answer: Separating error handling logic from the main code flow makes the code easier to read and understand, and simplifies the maintenance process.

19. Question 99: When is it appropriate *not* to use exceptions?

    • Answer: In performance-critical sections where the overhead of exception handling is unacceptable, or when dealing with low-level code where direct error handling is more efficient.

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