From 3688855976018096224 X-Google-Thread: f78e5,174aa7b34b06a51 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local01.nntp.dca.giganews.com!nntp.speakeasy.net!news.speakeasy.net.POSTED!not-for-mail NNTP-Posting-Date: Sun, 04 Dec 2005 12:10:02 -0600 Return-Path: X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) Delivered-To: std-c++@ucar.edu From: brangdon@cix.co.uk (Dave Harris) Newsgroups: comp.std.c++ Subject: Re: Is this really unspecified behavior? Message-ID: References: <1132786459.216137.307610@z14g2000cwz.googlegroups.com> Reply-To: brangdon@cix.co.uk X-Orig-X-Trace: individual.net +ho+bBjJp9zQonpVR07AjQPVwNf16dJhuurZcX21RgV9A9kk8= X-Virus-Scanned: amavisd-new at ucar.edu X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU Approved: Fergus Henderson , moderator of comp.std.c++ X-Virus-Scanned: amavisd-new at cs.mu.OZ.AU Date: Sun, 4 Dec 2005 12:05:31 CST Lines: 25 NNTP-Posting-Host: 65.182.171.162 X-Trace: sv3-eOm4+o71150ayCUT5onML+8JzLUvPunZtdTi6L3eEek3Aqgub+R3VQ0wdEV2/10rVARG/42G2+mft55!Uv6itmMG0BHdQlcEaG7ARjlOAzNf54xa7sZ84xKbhoMw+Wnbw98kXgDSd4KP+AmgyOZ8hyBB2yIl!7aSjKMJRMRWF4qn28Tlz X-Complaints-To: abuse@speakeasy.net X-DMCA-Complaints-To: abuse@speakeasy.net X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.32 Xref: g2news1.google.com comp.std.c++:2667 pongba@gmail.com () wrote (abridged): > It's just that I couldn't believe this little simple expression > has undefined behavior, though, I think you were right anyway. If you think of i as being stored as two words that are manipulated separately, then it becomes easier to see. You might get the high word of the new value and the low word of the old value. For example: i = 0x1000ffff; i = i++; might yield i == 0x1001ffff, which is different to (and much bigger than) any value that you would consider "correct". If i is a pointer, this could point to memory the application doesn't own, which could lead to a hardware fault even if *i is not accessed. And ints can have trapping values too. -- Dave Harris, Nottingham, UK. --- [ 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 ]