From -6618322605993293655 X-Google-Thread: f78e5,174aa7b34b06a51 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news1.google.com!newsread.com!news-xfer.newsread.com!nntp.abs.net!newsfeed.cw.net!cw.net!news-FFM2.ecrc.de!newsfeed.vmunix.org!newsfeed.stueberl.de!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: ben-public-nospam@decadentplace.org.uk (Ben Hutchings) Newsgroups: comp.std.c++ Subject: Re: Is this really unspecified behavior? Date: Wed, 30 Nov 2005 15:06:48 GMT Lines: 48 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: <1132629737.664847.151630@o13g2000cwo.googlegroups.com> <1132722639.345095.296070@f14g2000cwb.googlegroups.com> <200511231401.jANE1BuC092897@horus.isnic.is> <37hco1hvfg2s43q2dv3003her7im99airg@4ax.com> <1twif.776$iZ3.758@trndny03> <1133189252.960738.262510@g44g2000cwa.googlegroups.com> <1133276211.452281.106150@f14g2000cwb.googlegroups.com> NNTP-Posting-Host: news.news.demon.net X-Trace: news.demon.co.uk 1133363213 4883 158.152.254.254 (30 Nov 2005 15:06:53 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Wed, 30 Nov 2005 15:06:53 +0000 (UTC) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: slrn/0.9.8.1 (Debian) X-Orig-X-Trace: individual.net 3mwmdlX3t9sbr8fS7lweuwjRh3UwC4vAgIh4J125O1++4AVcI= X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU X-Reply-To: Ben Hutchings X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id jAUF6mPg015355; Thu, 1 Dec 2005 02:06:48 +1100 (EST) X-Path: comp-std-cpp-robomod!not-for-mail 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-Orig-Path: decadentplace.org.uk!news X-Newsgroups: comp.std.c++ Xref: g2news1.google.com comp.std.c++:2635 Sandor Hojtsy wrote: > You keep quoting the standard: > i = v[i++]; // the behavior is unspecified > i = 7, i++, i++; // i becomes 9 > i = ++i + 1; // the behavior is unspecified > i = i + 1; // the value of i is incremented > Note that this contains an identified defect, it should correctly read: > i = v[i++]; // the behavior is undefined > i = 7, i++, i++; // i becomes 9 > i = ++i + 1; // the behavior is undefined > i = i + 1; // the value of i is incremented > See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#351 > > I have a question: are these expressions undefined, or well-formed? They're all well-formed; that's a syntactical property. > i = i = 1; Despite the lack of a sequence point I believe this may be defined due to this wording in 5.17/1: "The result of the assignment operation is the value stored in the left operand *after* the assignment has taken place..." (my emphasis). > i = ++i; > a = (i = 1) + (i = 1); In these cases, the order of the two modifications of i is undefined, so they fall foul of 5/4. > If I take the standard word by word, they do not modify the value of i > twice in an expression, because one of the assignments is not > modification - just reassigning the existing value. All built-in assignment operators are considered to modify their left hand side, whether its value changes or not. -- Ben Hutchings Horngren's Observation: Among economists, the real world is often a special case. --- [ 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 ]