From -4504486881183913904 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,7522e5259f7267d6 X-Google-Attributes: gidf78e5,public From: Francis Glassborow Subject: x = y = z; Undefined? Date: 2000/01/14 Message-ID: #1/1 X-Deja-AN: 572396849 Approved: stephen.clamage@sun.com (comp.std.c++) References: <3876254a.30903561@news.csrlink.net> <3879ca08.3142429@news.csrlink.net> <387b3c32.7816532@news.csrlink.net> <387B6338.FCE9D984@sensor.com> <387bb7c0.39451037@news.csrlink.net> <387C7098.256766C8@wizard.net> <387cde71.28276175@news.csrlink.net> <387D1FC3.F19D5853@wizard.net> <387d50e4.57579814@news.csrlink.net> X-UID: 0000000001 X-Status: $$$T Organization: Southfield Microcomputer SS Mime-Version: 1.0 Reply-To: Francis Glassborow Newsgroups: comp.std.c++ Originator: clamage@taumet In article <387d50e4.57579814@news.csrlink.net>, John Potter writes > int i1, i2(2), i3(3); > (i1 = i2) += i3; > cout << i1 << endl; Any compiler of reasonable quality should be able to get such code correct because the potential undefined behaviour has not been hidden (e.g. by aliasing). I understood that one reason for writing the rules the way they are was that some systems have serious problems in writing to the same store with insufficient delay. Note that I am not a hardware expert and so this is hearsay. IMO compiler writers could do a much better job at detecting potential undefined behaviour and at least issuing a warning. Code such as: int i = 0; int array[10]; while (i<10) array[i] = i++; Has an easily diagnosed problem, it would be helpful if compilers issued warning for such code even if they include an assurance that they will generate safe code. OTOH void fn (int & i, int & j, int max, int * array) { i=0; while (i< max) array[i++] = j++; } Has potentially far worse undefined behaviour which cannot be reasonably diagnosed. Yes, I know the code stinks but have a look at some real code and you will find things just as rotten only masked by other code. Francis Glassborow Journal Editor, Association of C & C++ Users 64 Southfield Rd Oxford OX4 1PA +44(0)1865 246490 All opinions are mine and do not represent those of any organisation [ 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://reality.sgi.com/austern_mti/std-c++/faq.html ]