Exception handling (programming): Difference between revisions

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C++ <code>throw</code> clauses could specify any number of any types, even primitives and classes that did not extend <code>std::exception</code>.

Exception specifications were not enforced at compile-time. Violations resulted in the global function {{Cpp|std::unexpected}} being called.<ref name=bjarne-exc>[[Bjarne Stroustrup]], ''[[The C++ Programming Language]]'' Third Edition, [[Addison Wesley]], 1997. {{ISBN|0-201-88954-4}}. pp. 375-380.</ref> An empty exception specification could be given, which indicated that the function will throw no exception. This was not made the default when exception handling was added to the language because it would have required too much modification of existing code, would have impeded interaction with code written in other languages, and would have tempted programmers into writing too many handlers at the local level.<ref name=bjarne-exc/> Explicit use of empty exception specifications could, however, allow C++ compilers to perform significant code and stack layout optimizations that are precluded when exception handling may take place in a function.<ref name=cppeh /> Some analysts viewed the proper use of exception specifications in C++ as difficult to achieve.<ref>{{cite journal | title=Ten Guidelines for Exception Specifications | last=Reeves | first= J.W. | journal=C++ Report | volume=8 | issue=7 |date=July 1996}}</ref> This use of exception specifications was included in [[C++98]] and [[C++03]], [[deprecated]] in the 2012 C++ language standard ([[C++11]]),<ref>{{cite web |url=http://herbsutter.com/2010/03/13/trip-report-march-2010-iso-c-standards-meeting/ |title=Trip Report: March 2010 ISO C++ Standards Meeting |last=Sutter |first=Herb |author-link=Herb Sutter |date=3 March 2010 |access-date=24 March 2010 |url-status=live |archive-url=https://web.archive.org/web/20100323082634/http://herbsutter.com/2010/03/13/trip-report-march-2010-iso-c-standards-meeting/ |archive-date=23 March 2010 }}</ref> and was removed from the language in [[C++17]]. Throws clauses were replaced by {{Cpp|noexcept}} clauses. A function that will not throw any exceptions would now be denoted by the {{Cpp|noexcept}} keyword, and instead {{Cpp|noexcept(false)}} specified that a function will throw. Although <code>throw</code> clauses are removed from the language, writing only <code>throw()</code> in the signature is legal and is equivalent to <code>noexcept</code> (false)no exception specified by the <code>throw</code> clause denotes that it cannot throw). For transitioning a codebase that uses <code>throw</code> clauses, they can be adapted by instead redefining them with a macro to quickly resolve rejection of the removed <code>throw</code> clause by the compiler.

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