From -2790741060167799042 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,e94695845965b249 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1992-12-16 00:51:43 PST Newsgroups: comp.std.c++ Path: sparky!uunet!uunet.ca!frumious!pat From: pat@frumious.uucp (Patrick Smith) Subject: Re: Zero-length structures and pointer comparisons Message-ID: Date: Wed, 16 Dec 1992 08:42:55 GMT References: <9234423.15066@mulga.cs.mu.OZ.AU> <1992Dec9.133956.29659@lth.se> <1992Dec9.191606.5665@lucid.com> Organization: None Lines: 38 dag@seldon.control.lth.se (Dag Bruck) writes: | Suggested semantics: for any pointers p and q: | | p == q <=> ptrcmp(p,q) == 0 | | p != q <=> ptrcmp(p,q) != 0 | | ptrcmp(p,q) < 0 <=> ptrcmp(q,p) > 0 And transitivity: ptrcmp(p,q) <= 0 && ptrcmp(q,r) <= 0 => ptrcmp(p,r) <= 0 ptrcmp(p,q) <= 0 && ptrcmp(q,r) < 0 => ptrcmp(p,r) < 0 ptrcmp(p,q) < 0 && ptrcmp(q,r) <= 0 => ptrcmp(p,r) < 0 jss@lucid.com (Jerry Schwarz) writes: |And | | if p < q is defined, ptrcmp(p,q) < 0 <=> p < q This strikes me as nice to have, but not essential. Many applications of ptrcmp wouldn't need this property at all (eg. using ptrcmp to navigate through a binary tree, with no additional requirement on the ordering other than that it be an ordering). On the other hand, this might be fairly cheap, given that we're already insisting on p == q => ptrcmp(p,q) == 0 -- Patrick Smith uunet.ca!frumious!pat pat%frumious.uucp@uunet.ca