From 5023693499363807209 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,e94695845965b249 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1992-12-22 00:07:11 PST Newsgroups: comp.std.c++ Path: sparky!uunet!munnari.oz.au!metro!extro.ucc.su.OZ.AU!maxtal From: maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) Subject: Re: Zero-length structures and pointer comparisons Message-ID: <1992Dec22.003752.26023@ucc.su.OZ.AU> Sender: news@ucc.su.OZ.AU Nntp-Posting-Host: extro.ucc.su.oz.au Organization: MAXTAL P/L C/- University Computing Centre, Sydney References: <1992Dec18.192202.17023@ucc.su.OZ.AU> <9235622.25712@mulga.cs.mu.OZ.AU> Date: Tue, 22 Dec 1992 00:37:52 GMT Lines: 38 In article <9235622.25712@mulga.cs.mu.OZ.AU> fjh@munta.cs.mu.OZ.AU (Fergus James HENDERSON) writes: >maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) writes: > >>pat@frumious.uucp (Patrick Smith) writes: >>> p == q => ptrcmp(p,q) == 0 >> >> I'm NOT agreeing with this at present. I reject any relationship >>between p ? q and ptrcmp. On some machines any such relationship >>might make ptrcmp unimplementable, and thus defeat the proposal completely. > >I remain unconvinced that such a relationship is unimplementable on >some machines. On the 486 it is not in general possible to implement the comparison p==q for arbitrary logical addresses. If p and q are aliases only the operating system kernel could implement the comparison, and if the OS happened not to support this, p==q could not be implemented. > >>It is only Jims suggestion that ptrcmp might always return 0 that >>makes it possible to make its existence mandatory. > >A ptrcmp that always returned 0 would be useless, IMHO. > Not at all. My sort will still order the pointers into the total order, which in this case is anything. This is entirely different from the current situation where a sort based on the existing implementation defined < on pointers might not terminate. -- ;---------------------------------------------------------------------- JOHN (MAX) SKALLER, maxtal@extro.ucc.su.oz.au Maxtal Pty Ltd, 6 MacKay St ASHFIELD, NSW 2131, AUSTRALIA ;--------------- SCIENTIFIC AND ENGINEERING SOFTWARE ------------------