Exception handling (programming): Difference between revisions

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In [[computer programming]], several [[programming language|language]] mechanisms exist for '''exception handling'''. The term ''exception'' is typically used to denote a data structure storing information about an exceptional condition. One mechanism to transfer control, or ''raise'' an exception, is known as a ''throw''; the exception is said to be ''thrown''. Execution is transferred to a ''catch''.

== Usage ==

Programming languages differ substantially in their notion of what an exception is. Contemporary languages can roughly be divided into two groups:<ref name="Kiniry">{{Cite book | doi = 10.1007/11818502_16| chapter = Exceptions in Java and Eiffel: Two Extremes in Exception Design and Application| title = Advanced Topics in Exception Handling Techniques| volume = 4119| pages = 288–300| series = Lecture Notes in Computer Science| year = 2006| last1 = Kiniry | first1 = J. R. | isbn = 978-3-540-37443-5|url=http://staffwww.dcs.shef.ac.uk/people/A.Simons/remodel/papers/ExceptionsInEiffelAndJava.pdf}}</ref><ref group=note>PL/I used dynamically scoped exceptions. PL/I exception handling included events that are not errors, e.g., attention, end-of-file, modification of listed variables.{{Citation needed|date=June 2020}}</ref>

*Programming Languageslanguages wherediffer exceptionssubstantially arein designedtheir tonotion of what an exception is. Exceptions can be used asto flowrepresent controland structures:handle Adaabnormal, Modula-3unpredictable, ML,erroneous OCamlsituations, PL/I,but Python,also andas Rubyflow fallcontrol instructures thisto categoryhandle normal situations. For example, [[Iterator#Python|Python's iterators]] throw StopIteration exceptions to signal that there are no further items produced by the iterator.<ref>{{cite web |title=Built-in Exceptions — Python 3.10.4 documentation |url=https://docs.python.org/3/library/exceptions.html#StopIteration |website=docs.python.org |access-date=17 May 2022}}</ref> There is disagreement within many languages as to what constitutes idiomatic usage of exceptions. For example, Joshua Bloch states that Java's exceptions should only be used for exceptional situations,<ref name="EffectiveJava">

* Languages where exceptions are only used to handle abnormal, unpredictable, erroneous situations: C++,<ref>{{cite web|url=http://www.stroustrup.com/bs_faq2.html#exceptions-what-not|title=Stroustrup: C++ Style and Technique FAQ|website=www.stroustrup.com|access-date=5 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180202012417/http://www.stroustrup.com/bs_faq2.html#exceptions-what-not|archive-date=2 February 2018}}</ref> Java,<ref name="EffectiveJava">

{{cite book

| last = Bloch

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| chapter-url = https://archive.org/details/effectivejava00bloc_0/page/241

| edition = Second

}}</ref> but Kiniry observes that Java's built-in {{java|FileNotFoundException}} is not at all an exceptional event.<ref name="Kiniry">{{Cite book | doi = 10.1007/11818502_16| chapter = Exceptions in Java and Eiffel: Two Extremes in Exception Design and Application| title = Advanced Topics in Exception Handling Techniques| volume = 4119| pages = 288–300| series = Lecture Notes in Computer Science| year = 2006| last1 = Kiniry | first1 = J. R. | isbn = 978-3-540-37443-5|url=http://staffwww.dcs.shef.ac.uk/people/A.Simons/remodel/papers/ExceptionsInEiffelAndJava.pdf}}</ref> Similarly, Bjarne Stroustrup, author of C++, states that C++ exceptions should only be used for error handling, as this is what they were designed for,<ref>{{cite web|url=http://www.stroustrup.com/bs_faq2.html#exceptions-what-not|title=Stroustrup: C++ Style and Technique FAQ|website=www.stroustrup.com|access-date=5 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180202012417/http://www.stroustrup.com/bs_faq2.html#exceptions-what-not|archive-date=2 February 2018}}</ref> but Kiniry observes that many modern languages such as Ada, C++,

}}</ref> C#, Common Lisp, Eiffel, and Modula-2.

ProgrammingModula-3, ML and OCaml, Python, and Ruby use exceptions for flow control. Some languages differsuch substantiallyas inEiffel, C#, Common Lisp, and Modula-2 have made a concerted effort to restrict their notionusage of whatexceptions, analthough exceptionthis is. Contemporarydone languageson cana roughlysocial berather dividedthan intotechnical two groups:level.<ref name="Kiniry">{{Cite book | doi = 10.1007/11818502_16| chapter = Exceptions in Java and Eiffel: Two Extremes in Exception Design and Application| title = Advanced Topics in Exception Handling Techniques| volume = 4119| pages = 288–300| series = Lecture Notes in Computer Science| year = 2006| last1 = Kiniry | first1 = J. R. | isbn = 978-3-540-37443-5|url=http://staffwww.dcs.shef.ac.uk/people/A.Simons/remodel/papers/ExceptionsInEiffelAndJava.pdf}}</ref><ref group=note>PL/I used dynamically scoped exceptions. PL/I exception handling included events that are not errors, e.g., attention, end-of-file, modification of listed variables.{{Citation needed|date=June 2020}}</ref>

== History ==