What\'s the True Cost of Exceptions in C : Exploring the Hidden Performance Impacts?

Exceptions in C : A Behind-the-Scenes Analysis

Introduction

Despite numerous claims about the potential slowness of exceptions, definitive evidence has been elusive. This article aims to demystify the inner workings of exceptions in C to provide insights for their effective usage and assessment of their performance implications.

Delving into Exception Handling

Contrary to popular belief, exceptions do not inherently incur significant overhead on the normal code path. Instead, the compiler cleverly generates out-of-line fixup code blocks stored in separate tables. These tables guide the exception handling process through the standard library's functions, which handle steps such as:

• Stack unwinding to the appropriate exception handler
• Location of matching exception handlers
• Execution of the chosen handler

Throwing an Exception Step by Step

The process of throwing an exception involves several key actions:

• Calling __cxa_allocate_exception to reserve memory for the exception object
• Initializing the exception object with its type and relevant data
• Using __cxa_throw to trigger the exception handling mechanism
• This function initiates the stack unwinding and search for the proper handler

Disentangling the True Cost of Exceptions

While exceptions do not introduce direct overhead under normal circumstances, their usage can incur performance penalties during exception thrown and capture. When an exception is thrown, the runtime incurs the following costs:

• Table parsing and handler execution
• Stack unwinding to the proper exception handler

Conclusion

The overhead associated with exceptions in C primarily stems from the exception throwing and catching processes. Nevertheless, by using exceptions for genuine exceptional situations rather than routine error handling, it is possible to minimize their impact. In scenarios where errors are infrequent, the absence of explicit error checking can actually result in improved performance.

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