From 8554287935781614024 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,96a8c01f7043c2d9 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2002-09-27 05:12:09 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!mutlu.news.demon.net!demon!mail2news.demon.co.uk!devnull From: glancaster@ntlworld.com ("Garry Lancaster") Newsgroups: comp.std.c++ Subject: Re: Proposal: exception stack unwinding resumption Date: Fri, 27 Sep 2002 11:53:54 +0000 (UTC) Organization: ntl Cablemodem News Service Lines: 130 Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <6df0c6a8.0208260746.633710cb@posting.google.com><23b84d65.0209161107.23bea618@posting.google.com><6df0c6a8.0209170602.2cb54634@posting.google.com><6df0c6a8.0209201925.6faa9e57@posting.google.com><6df0c6a8.0209230602.2aba3ca8@posting.google.com><6df0c6a8.0209240716.6fb5ec00@posting.google.com> X-Trace: mail2news.demon.co.uk 1033127634 4269 10.0.0.1 (27 Sep 2002 11:53:54 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Fri, 27 Sep 2002 11:53:54 +0000 (UTC) X-Received: from mulga.cs.mu.oz.au ([128.250.1.22]) by news.demon.co.uk with esmtp (Exim 4.05) id 17utgu-00016i-00 for mail2news@news.news.demon.net; Fri, 27 Sep 2002 11:53:52 +0000 X-Received: from localhost (localhost [[UNIX: localhost]]) by mulga.cs.mu.OZ.AU id VAA29313; Fri, 27 Sep 2002 21:53:19 +1000 (EST) X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Path: comp-std-cpp-robomod!not-for-mail X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Delivered-To: std-c++@ncar.ucar.edu X-Newsgroups: comp.std.c++ X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 X-NNTP-Posting-Date: Fri, 27 Sep 2002 10:38:20 BST X-MailScanner: PASSED (v1.2.6 65811 g8R9cT3e082122 mailbox1.ucsd.edu) Xref: archiver1.google.com comp.std.c++:14258 Pierre Baillageon: > >> I'd like to be corrected if I'm wrong, but I'm quite certain that if > >> ~A() throws, all its data members and base classes are destructed. The > >> relevant clause, I believe, is 15.2, where it is said that partially > >> constructed objects will have their fully constructed parts destroyed > >> properly. It even mention that it works for arrays. Bob Bell: > >I don't have a copy of the standard, but I'll give you my > >understanding of the language. Perhaps someone else who does have the > >standard can settle this for us. > > > >"Partially constructed objects" refers to exceptions that are thrown > >by a constructor, not a destructor. The intent is for the language to > >guarantee that objects the programmer cannot access are destroyed > >(since the object has not yet finished constructing, the programmer > >has not been able to obtain a reference to it). > > > >If an exception is thrown from some function that is _not_ a > >constructor, then only stack objects are destroyed. Therefore, if > >A::~A above throws, since the B part is not a stack object, B::~B will > >not be called. > > > >I'd be interested in anybody else's opinion on this as well. I just > >ran a quick test in CodeWarrior 7, and it seems to agree with my > >interpretation. Francis Glassborow: > I am not sure that the Standard actually deals with this. There quite a > number of corner problems with dtors which matter not at all until > people want to push the boundaries. But it matters not, because > supposing that the base subobject dtors are called all they do is make > matters worse by ensuring that you have a ghost object with some of its > limbs missing. > > However I have just looked up the requisite part of the C++ Standard. > 15.2 para 2 starts: > > An object that is partially constructed or partially destroyed will have > destructors executed for all of its fully constructed subobjects, that > is, for subobjects for which the constructor has completed execution and > the destructor has not yet begun execution. > > That makes it quite clear either CodeWarrior got it wrong or your test > is faulty. There are two more possibilities: 1. We misinterpret the standard. 2. The standard has a defect. Let's say we have something like this: #include #include #include class B { public: ~B() { std::cout << "~B\n"; if( std::uncaught_exception() ) std::cout << "Unwinding.\n"; throw std::string( "~B" ); } }; class A : public B { public: ~A() std::cout << "~A\n"; throw std::string( "~A" ); } }; int main() { try { A a; } catch(const std::string s) { std::cout << "Caught exception thrown by " << s << ".\n"; } std::cout << "Exiting normally.\n"; } If I understand Bob Bell's reasoning correctly, he is saying that the program should print: ~A Caught exception thrown by ~A. Exiting normally. I wonder if CodeWarrior 7 would agree? MSVC7 gives: ~A ~B Unwinding. then terminates. and Borland C++ Builder 5 gives: ~A ~B then terminates. Make of this what you will. Kind regards Garry Lancaster Codemill Ltd Visit our web site at http://www.codemill.net --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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