From -4014339613273917725 X-Google-Thread: f78e5,174aa7b34b06a51 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!news.glorb.com!molokai.public-internet.co.uk!newspeer.public-internet.co.uk!peer.news.zetnet.net!194.159.246.34.MISMATCH!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: nagle@animats.com (John Nagle) Newsgroups: comp.std.c++ Subject: Re: Is this really unspecified behavior? Date: Sun, 18 Dec 2005 05:40:16 GMT Organization: SBC http://yahoo.sbc.com Lines: 50 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <1132759176.368850.264850@g43g2000cwa.googlegroups.com> <1132933832.802917.153350@g14g2000cwa.googlegroups.com> <1133551647.532929.325730@z14g2000cwz.googlegroups.com> <1133583412.951239.208510@g49g2000cwa.googlegroups.com> <1133910546.716987.80030@g14g2000cwa.googlegroups.com> <0l5ep1ppfhdj5p1pcu7e4na4ub0vjajlq3@4ax.com> <200512161412.jBGECcuC061966@horus.isnic.is> <87bqzfp5t2.fsf@boost-consulting.com> NNTP-Posting-Host: news.news.demon.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Trace: news.demon.co.uk 1134884423 3768 158.152.254.254 (18 Dec 2005 05:40:23 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Sun, 18 Dec 2005 05:40:23 +0000 (UTC) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.11) Gecko/20050728 X-Accept-Language: en-us, en, ja X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU X-UserInfo1: O@YORZSDTBSUCFH[OZK@_TDAYZOZ@GXOXZ^D]\YIJYWZUYICD^RAQBKZQTZTX\_I[^G_KGFNON[ZOE_AZNVO^\XGGNTCIRPIJH[@RQKBXLRZ@CD^HKANYVW@RLGEZEJN@\_WZJBNZYYKVIOR]T]MNMG_Z[YVWSCH_Q[GPC_A@CARQVXDSDA^M]@DRVUM@RBM X-Path: comp-std-cpp-robomod!not-for-mail X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id jBI5eGgP024388; Sun, 18 Dec 2005 16:40:16 +1100 (EST) X-NNTP-Posting-Date: Sun, 18 Dec 2005 00:30:27 EST X-Delivered-To: std-c++@ucar.edu X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Newsgroups: comp.std.c++ Xref: g2news1.google.com comp.std.c++:2815 David Abrahams wrote: > howard.hinnant@gmail.com (Howard Hinnant) writes: > > >>In article , >> dave@boost-consulting.com (David Abrahams) wrote: >> >> >>>>The problem with the current language definition >>>>is that the compiler has too much freedom to reorder >>>>expressions, and that leads to unsafe code. What's really going on here is that the sequence of events from the "new" to the assignment of the result of auto_ptr is an atomic operation. Either it needs to run to completion or it needs to have no effect. The way you protect an atomic operation is to enclose it in a try block. You can't do that inside an expression. Actually, the problem is that the compiler doesn't know enough about side effects. Properly, functions without side effects are reorderable (and even subject to folding of multiple calls), while functions with side effects should not be reordered. The most elegant solution is that the compiler should know, for inlines and well-known library functions, which functions have no side effects. (Throwing an exception is a side effect here.) Reordering of calls in the presence of potential side effects should be prohibited. If a function is too complex to resolve the side effect issue or not inline, it's best to assume that it has side effects. If it's a big function, the small speed benefits of reordering won't matter anyway. John Nagle --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ]