C++ Exception Handling Interview Questions and Answers for 2 years experience

1. What is exception handling?

   • Answer: Exception handling is a mechanism in C++ to manage runtime errors gracefully. Instead of letting the program crash, it allows you to catch and handle errors, preventing unexpected termination and providing a more robust application.

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 basic syntax of a try-catch block.

   • Answer: ```c++ try { // Code that might throw an exception } catch (ExceptionType exceptionVariable) { // Handle the exception } ```

4. What is a `throw` statement? Give an example.

   • Answer: The throw statement initiates the exception handling process. It throws an exception object of a specific type. ```c++ if (value < 0) { throw std::runtime_error("Value cannot be negative"); } ```

5. What is a `catch` block? How does it work?

   • Answer: A catch block handles exceptions thrown by the corresponding try block. It specifies the type of exception it can handle and provides code to manage the error. If an exception is thrown and a matching catch block is found, the code within that block is executed.

6. What is the purpose of exception specifications (deprecated)?

   • Answer: Exception specifications, declared using throw(), were used to specify which exceptions a function could throw. However, they are now considered deprecated because they caused more problems than they solved. Modern C++ prefers using noexcept instead.

7. What is the difference between `catch(...)` and specific exception handling?

   • Answer: `catch(...)` is a catch-all block that handles any exception. Specific exception handling uses catch blocks that specify the exception type. Specific handling is preferred for better error management and more informative error messages. `catch(...)` should be used sparingly and with caution as it masks potential errors.

8. What are standard exception classes in C++? Give examples.

   • Answer: The standard library provides several exception classes in ``, including: `std::exception`, `std::runtime_error`, `std::logic_error`, `std::out_of_range`, `std::invalid_argument`. `std::runtime_error` is for runtime errors like file opening failures, while `std::logic_error` is for errors arising from programming logic (e.g., passing invalid arguments).

9. Explain the importance of exception safety.

   • Answer: Exception safety ensures that resources are properly managed and the program's state remains consistent even when exceptions occur. This prevents memory leaks, data corruption, and other issues that might lead to program instability. Three levels of exception safety are commonly discussed: basic, strong, and nothrow.

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

    • Answer: RAII is a programming idiom where resources (like memory, files, network connections) are managed by objects with destructors. When an exception occurs, the destructors are automatically called, ensuring resources are released, thus contributing to exception safety.

11. Describe how to handle exceptions in constructors and destructors.

    • Answer: In constructors, exceptions should be handled carefully to avoid resource leaks. If an exception occurs during constructor execution, the object is not fully constructed. Destructors should not throw exceptions; they should always clean up resources reliably even in exceptional cases.

12. What is `std::uncaught_exception()`? When would you use it?

    • Answer: `std::uncaught_exception()` checks if an exception is currently being handled but not yet caught. It can be used to prevent re-throwing the same exception from within an exception handler (avoiding infinite loops). This is less frequently needed in modern C++ due to the improvements in exception handling.

13. Explain the concept of exception hierarchies.

    • Answer: Exception hierarchies involve creating custom exception classes that inherit from other exception classes. This allows for more specific exception handling and categorization of errors. It promotes code organization and readability by grouping related exceptions.

14. How to define your own custom exception classes? Give an example.

    • Answer: Custom exception classes are typically derived from `std::exception` or its derivatives. ```c++ class MyException : public std::runtime_error { public: MyException(const std::string& message) : std::runtime_error(message) {} }; ```

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

    • Answer: While C++ doesn't explicitly have "checked" and "unchecked" exceptions like some other languages (e.g., Java), the concept is analogous to handling exceptions explicitly vs. relying on `catch(...)`. Specific exception handling is closer to checked exceptions, while relying on `catch(...)` is similar to handling unchecked exceptions – less specific and potentially hiding problems.

16. Discuss the benefits and drawbacks of exception handling.

    • Answer: Benefits: Improved error handling, more robust code, cleaner code structure (separation of error handling from main logic), better maintainability. Drawbacks: Performance overhead (although generally small), potential complexity if overused, possibility of masking errors (especially with `catch(...)`).

17. When should you avoid using exceptions?

    • Answer: Avoid exceptions for handling conditions that are expected to occur frequently and are easily handled within the normal flow of the program (e.g., checking for valid user input). Exceptions are better suited for unexpected errors that disrupt the normal flow.

18. How can you improve the performance of exception handling?

    • Answer: Minimize the use of exceptions in performance-critical sections of code. Use more efficient error handling techniques for commonly occurring, predictable errors. Properly design your exception hierarchy to reduce search time in `catch` statements.

19. Explain the noexcept specifier.

    • Answer: `noexcept` specifies that a function will not throw exceptions. This allows for compiler optimizations and helps ensure exception safety. It's a good practice to use `noexcept` where appropriate.

20. How does exception handling interact with destructors?

    • Answer: Destructors are always called when an object goes out of scope, even if an exception is thrown. This is crucial for resource cleanup. This interaction is a cornerstone of RAII.

21. Describe stack unwinding.

    • Answer: Stack unwinding is the process of the runtime system cleaning up the stack when an exception is thrown and caught. This involves calling destructors for objects on the stack, releasing resources, and transferring control to the appropriate `catch` block.

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