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copied!<p>The key thing an exception implementation needs to handle is how to return to the exception handler once an exception has been thrown. Since you may have made an arbitrary number of nested function calls since the try statement in C++, it must <em>unwind the call stack</em> searching for the handler. However implemented, this must incur the <strong>code size cost</strong> of maintaining sufficient information in order to perform this operation (and generally means a table of data for calls that can take exceptions). It also means that the dynamic code <strong>execution path will be longer</strong> than simply returning from functions calls (which is a fairly inexpensive operation on most platforms). There may be other costs as well depending on the implementation.</p> <p>The relative cost will vary depending on the language used. The higher-level language used, the less likely the code size cost will matter, and the information may be retained regardless of whether exceptions are used.</p> <p>An application where the use of exceptions (and C++ in general) is often avoided for good reasons is embedded firmware. In typical small bare metal or RTOS platforms, you might have 1MB of code space, or 64K, or even smaller. Some platforms are so small, even C is not practical to use. In this kind of environment, the size impact is relevant because of the cost mentioned above. It also impacts the standard library itself. Embedded toolchain vendors will often produce a library without exception capability, which has a huge impact on code size. Highly optimizing compilers may also analyze the callgraph and optimize away needed call frame information for the unwind operation for considerable space reduction. Exceptions also make it more difficult to analyze hard real-time requirements.</p> <p>In more typical environments, the code size cost is almost certainly irrelevant and the performance factor is likely key. Whether you use them will depend on your performance requirements and how you want to use them. Using exceptions in non-exceptional cases can make an elegant design, but at a performance cost that may be unacceptable for high performance systems. Implementations and relative cost will vary by platform and compiler, so the best way to truly understand if exceptions are a problem is to analyze your own code's performance.</p>

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