From -458153549922551695 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,edb7b260f2974eab X-Google-Attributes: gidf78e5,public From: Tom Payne Subject: Re: C/C++ object identity (was: C++ briar patch (Was: Object IDs are bad)) Date: 1997/05/28 Message-ID: <5midmt$4t9@skylark.ucr.edu>#1/1 X-Deja-AN: 244650947 References: <5l27qb$2fm$1@Masala.CC.UH.EDU> <5lbffe$dhb$1@goanna.cs.rmit.edu.au> <5lotr8$e7n@mulga.cs.mu.OZ.AU> <5lrc40$5e0@mulga.cs.mu.OZ.AU> <3383ED66.5622@strip_these_words.ix.netcom.com> <5m1upg$olo@mulga.cs.mu.OZ.AU> X-Original-Date: 28 May 1997 23:05:01 GMT Organization: Dept. Computer Science, UCR X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBVAwUBM40TCEy4NqrwXLNJAQH/KQIAicps40NKzi7pmFPvREO6k44U/5a6vt8W HDFwAcY3WbCeS32tyg+HEJZ4TgoUKk5DBh2TUvItd9hBNmizYt4jvw== =nGgI Newsgroups: comp.std.c++ Originator: austern@isolde.mti.sgi.com In comp.std.c++ Fergus Henderson wrote: [...] : When I said "If `==' was really intended to be undefined ...", : I meant "If the C standard committee had really intended to make : the results of `==' undefined ...". [...] : Hyopthetically assuming that the C standard committee had really : intended to make the results of `==' on ponters to unrelated objects : undefined, I used to subscribe to that hypothesis, but 6.3.9 (Equality operators) states: "Contraints One of the following shall hold: --- ... ; --- both operands are pointers to qualified or unqualified versions of compatible types; --- ... ; or --- ... ." In particular, it makes no restriction that the referrents of these pointers be related. Granted, 6.3.9 goes on to say: Where the operands have types and values suitable for the relational operators, the semantics detailed in 6.3.8 apply. But unrelated objects apparently are not "suitable for the relational operator" ( <, >, <= and >= ), since, according to 6.3.8: If the objects pointed to are not members of the same aggregate or union object, the result is undefined. ... I thought that the above 6.3.8 clause applied to equality operators, since 6.3.8 goes on to discusses conditions under which pointers "compare equal". A more careful reading indicates that it applies only to the relational operators, which seem to have a strictly smaller domain than the equality operators. Tom Payne --- [ comp.std.c++ is moderated. To submit articles: Try just posting with your newsreader. If that fails, use mailto:std-c++@ncar.ucar.edu comp.std.c++ FAQ: http://reality.sgi.com/austern/std-c++/faq.html Moderation policy: http://reality.sgi.com/austern/std-c++/policy.html Comments? mailto:std-c++-request@ncar.ucar.edu ]