Why Doesn\'t C Use Nested Exceptions for Destructor Throws?

Why Doesn't C Use Nested Exceptions to Allow Throwing from Destructors?

While it is generally inadvisable to throw exceptions from destructors, there have been proposals to utilize nested exceptions in such scenarios. However, this idea has not been implemented due to certain limitations.

Nested Exceptions vs. std::terminate

When an exception is thrown from a destructor, another exception may be "in flight." Nested exceptions allow for multiple exceptions to be stacked, but in this case, it is not immediately clear how to handle the situation. Historically, it was decided that std::terminate (or its associated handler std::terminate_handler) should be called.

Limitations of Nested Exceptions

While nested exceptions could potentially solve the issue of throwing from destructors, there are practical limitations:

• Runtime Performance: Nested exceptions can introduce runtime overhead compared to calling std::terminate. This overhead may be negligible in most cases, but it could be relevant in performance-critical applications.
• Compatibility with Existing Code: std::terminate is a well-established mechanism for handling uncaught exceptions. Changing this behavior could break existing code that relies on this behavior.

Current Status and Future Prospects

As of C 11 and C 14, nested exceptions are not used for throwing from destructors. std::terminate remains the default behavior. However, this may be subject to change in future C versions if potential performance and compatibility issues are resolved.

Alternative Approaches

Instead of throwing from destructors, alternative approaches can be considered:

• Use RAII principles: Implement resource acquisition is initialization (RAII) to ensure that resources are managed correctly without the need for destructors.
• Employ custom exception handlers: Define custom exception handlers that can handle specific exception scenarios, including those related to destructors.
• Avoid throwing from destructors: Generally, it is recommended to avoid throwing from destructors unless absolutely necessary.

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