Why Don\'t C Destructors Throw Exceptions Using `std::nested_exception`?

Nested Exceptions in C : Why Aren't They Used for Throwing from Destructors?

Introduction

Throwing exceptions from destructors poses a unique challenge: handling potential concurrent exceptions. C designers deliberately opted against using the std::nested_exception feature to address this issue, favoring std::terminate instead. This article explores the rationale behind this decision and discusses the limitations of using nested exceptions in this context.

Nested Exceptions: A Brief Overview

std::nested_exception is a class introduced in C 11 that allows for nesting exceptions. This feature enables exception propagation without overwriting the currently thrown exception. In theory, this could provide a solution for throwing exceptions from destructors.

Issues with Using std::nested_exception

However, several challenges arise when attempting to use std::nested_exception for throwing exceptions from destructors:

• Ambiguous Error Reporting: If a nested exception is thrown from a destructor while another exception is already in flight, it becomes unclear which exception should be reported. The current exception may be relevant to the destructor's execution or merely a coincident coincidence.
• Incomplete Exception Handling: If an exception is thrown from a destructor, it may not be possible to determine which objects have already completed their destruction. This complicates exception handling and may lead to unexpected resource leaks or program crashes.

Decision to Use std::terminate

Given these concerns, the C designers decided that std::terminate is a more appropriate approach when a destructor attempts to throw an exception. std::terminate effectively terminates the program, providing a definitive solution to the simultaneous exception handling problem.

Exceptions as Propagators

One of the intended uses of std::nested_exception is to serve as a propagator of exceptions. By nesting an exception within another, one can provide additional context and information about the error. However, this functionality is not suitable for throwing exceptions from destructors. The reason is that destructors are meant to clean up resources, not to propagate errors.

Conclusion

Nested exceptions offer a valuable mechanism for error handling in C , but throwing exceptions from destructors introduces unique challenges best addressed through the use of std::terminate. The limitations of nested exceptions in this context, including ambiguous error reporting and incomplete exception handling, make std::terminate a more reliable and practical solution.

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