Скачать или смотреть How to Properly Override the what() Method in C+ + Custom Exceptions

Learn how to correctly override the `what()` method from std::exception in your C+ + custom exceptions and avoid common pitfalls.
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This video is based on the question https://stackoverflow.com/q/67848525/ asked by the user 'Richard Neumann' ( https://stackoverflow.com/u/3515670/ ) and on the answer https://stackoverflow.com/a/67848564/ provided by the user 'John Zwinck' ( https://stackoverflow.com/u/4323/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Overriding the what() Method in C+ +

In C+ + , when creating custom exceptions that derive from the std::exception class, one often encounters the need to override the what() method. This method returns a C-style string (const char*) that describes the exception. An issue that developers may face is when their Integrated Development Environment (IDE) warns them that the what() function is "hiding a non-virtual function" from the std::exception class. This can be confusing, especially for those who are attempting to follow best practices by properly overriding methods.

What Does the Warning Mean?

The warning you received from your IDE suggests that C+ + 's method hiding is in play. This occurs under specific circumstances:

When a derived class defines a method with the same name as a base class method, it doesn't explicitly override it unless the base class function is marked as virtual.

The std::exception class has a what() method that is virtual, so proper overriding should occur without any issues. However, your IDE might misinterpret your use of [[nodiscard]] or other context as a hint that you are hiding rather than overriding the method.

The Solution: Correctly Overriding the what() Method

To ensure you are correctly overriding the what() method and avoid these IDE warnings, follow the steps outlined below:

Step 1: Define Your Custom Exception Class

When creating your custom exception class, ensure that it extends from std::exception. Use the noexcept specifier for the what() method, and omit any unnecessary attributes like [[nodiscard]] that might introduce confusion.

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Step 2: Implement the what() Method

In the implementation file, ensure the what() method is defined properly. You have the right idea by returning a string that describes the exception. The static string literal is appropriate here since it will reside in read-only memory.

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Step 3: Avoid Common Pitfalls

Do Not Use [[nodiscard]]: This attribute might not serve a purpose in this context and could potentially lead to the confusion that caused your IDE's warning. It's best to keep the method declaration clean and straightforward.

Use Good Documentation: Always document how and why your custom exceptions are thrown, providing users of your code with valuable information.

Conclusion

Creating custom exceptions in C+ + that extend std::exception is a straightforward process when you know how to properly override methods like what(). While IDEs can sometimes give misleading warnings, ensuring your method signatures are correct and avoiding unnecessary attributes can significantly reduce such confusion.

By understanding how to implement and override functionalities properly, you can create more robust and maintainable code in your C+ + projects.