Error Handling Without Exceptions
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Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like error in exception handler the stream or file you, helping each other. Join them; it only takes a minute: Sign up Why is exception handling bad? up vote 62 down vote favorite 31 Google's Go language has no exceptions as a design choice, and Linus of
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Linux fame has called exceptions crap. Why? exception exception-handling error-handling error-reporting share|improve this question edited Sep 21 '11 at 3:23 Trott 27.9k1470129 asked Nov 15 '09 at 0:38 joemoe 3,03853149 2 Creator of ZeroMQ writes about how he thinks it was a mistake to write it in C++ (mostly because of the error handling) 250bpm.com/blog:4 –serbaut Oct 20 '12 at 19:13 add a comment| 16 Answers 16 active oldest votes up vote 51 down laravel4 error in exception handler vote accepted Exceptions make it really easy to write code where an exception being thrown will break invariants and leave objects in an inconsistent state. They essentially force you to remember that most every statement you make can potentially throw, and handle that correctly. Doing so can be tricky and counter-intuitive. Consider something like this as a simple example: class Frobber { private: int m_NumberOfFrobs; FrobManager m_FrobManager; public: void Frob() { m_NumberOfFrobs++; m_FrobManager.HandleFrob(new FrobObject()); } }; Assuming the FrobManager will delete the FrobObject, this looks OK, right? Or maybe not... Imagine then if either FrobManager::HandleFrob() or operator new throws an exception. In this example, the increment of m_NumberOfFrobs does not get rolled back. Thus, anyone using this instance of Frobber is going to have a possibly corrupted object. This example may seem stupid (ok, I had to stretch myself a bit to construct one :-)), but, the takeaway is that if a programmer isn't constantly thinking of exceptions, and making sure that every permutation of state gets rolled back whenever there are throws, you get into trouble this way. As an example, you can think of it like you think of mutexes. Inside a critical section, you rely on several statements to make sure that data structures are not corrupted and that other threads can't see your intermediate values. If any one of those stat
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View exceptions Save to: Instapaper Pocket Readability Exceptions and Error Handling Why use exceptions? What good can using exceptions do for me? exception handling in c++ example programs The basic answer is: Using exceptions for error handling makes your code simpler, cleaner, and less likely to miss errors. But what's wrong with "good old errno and if-statements"? The basic answer is: Using those, http://stackoverflow.com/questions/1736146/why-is-exception-handling-bad your error handling and your normal code are closely intertwined. That way, your code gets messy and it becomes hard to ensure that you have dealt with all errors (think "spaghetti code" or a "rat's nest of tests"). First of all there are things that just can't be done right without exceptions. Consider an error detected in a constructor; how do you report the error? You throw an exception. That's the basis https://isocpp.org/wiki/faq/exceptions of RAII (Resource Acquisition Is Initialization), which is the basis of some of the most effective modern C++ design techniques: A constructor's job is to establish the invariants for the class (create the environment in which the member functions are to run) and that often requires the acquisition of resources, such as memory, locks, files, sockets, etc. Imagine that we did not have exceptions, how would you deal with an error detected in a constructor? Remember that constructors are often invoked to initialize/construct objects in variables: vector
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and http://programmers.stackexchange.com/questions/184654/ive-been-told-that-exceptions-should-only-be-used-in-exceptional-cases-how-do policies of this site About Us Learn more about Stack Overflow the http://www.boost.org/community/error_handling.html company Business Learn more about hiring developers or posting ads with us Programmers Questions Tags Users Badges Unanswered Ask Question _ Programmers Stack Exchange is a question and answer site for professional programmers interested in conceptual questions about software development. Join them; it only takes a minute: Sign up error in Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top I've been told that Exceptions should only be used in exceptional cases. How do I know if my case is exceptional? up vote 77 down vote favorite 15 My specific case here is that the user can error in exception pass in a string into the application, the application parses it and assigns it to structured objects. Sometimes the user may type in something invalid. For example, their input may describe a person but they may say their age is "apple". Correct behavior in that case is roll back the transaction and to tell the user an error occurred and they'll have to try again. There may be a requirement to report on every error we can find in the input, not just the first. In this case, I argued we should throw an exception. He disagreed, saying, "Exceptions should be exceptional: It's expected that the user may input invalid data, so this isn't an exceptional case" I didn't really know how to argue that point, because by definition of the word, he seems to be right. But, it's my understanding that this is why Exceptions were invented in the first place. It used to be you had to inspect the result to see if an error occurred. If you failed to check, bad things could happen without you not
is a good introduction to some of the issues of writing robust generic components: D. Abrahams: ``Exception Safety in Generic Components'', originally published in M. Jazayeri, R. Loos, D. Musser (eds.): Generic Programming, Proc. of a Dagstuhl Seminar, Lecture Notes on Computer Science. Volume. 1766 Guidelines When should I use exceptions? The simple answer is: ``whenever the semantic and performance characteristics of exceptions are appropriate.'' An oft-cited guideline is to ask yourself the question ``is this an exceptional (or unexpected) situation?'' This guideline has an attractive ring to it, but is usually a mistake. The problem is that one person's ``exceptional'' is another's ``expected'': when you really look at the terms carefully, the distinction evaporates and you're left with no guideline. After all, if you check for an error condition, then in some sense you expect it to happen, or the check is wasted code. A more appropriate question to ask is: ``do we want stack unwinding here?'' Because actually handling an exception is likely to be significantly slower than executing mainline code, you should also ask: ``Can I afford stack unwinding here?'' For example, a desktop application performing a long computation might periodically check to see whether the user had pressed a cancel button. Throwing an exception could allow the operation to be cancelled gracefully. On the other hand, it would probably be inappropriate to throw and handle exceptions in the inner loop of this computation because that could have a significant performance impact. The guideline mentioned above has a grain of truth in it: in time critical code, throwing an exception should be the exception, not the rule. How should I design my exception classes? Derive your exception class from std::exception. Except in *very* rare circumstances where you can't afford the cost of a virtual table, std::exception makes a reasonable exception base class, and when used universally, allows programmers to catch "everything" without resorting to catch(...). For more about catch(...)