From 947367156421743957 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,e94695845965b249 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1992-12-03 23:35:47 PST Newsgroups: comp.std.c++ Path: sparky!uunet!mcsun!sunic!lth.se!dag From: dag@control.lth.se (Dag Bruck) Subject: Re: Zero-length structures and pointer comparisons Message-ID: <1992Dec4.070720.13056@lth.se> Sender: news@lth.se Organization: Department of Automatic Control, Lund, Sweden References: <1992Nov30.195202.14370@ucc.su.OZ.AU> <1992Dec1.072440.824@jyu.fi> <1992Dec1.175548.16232@meaddata.com> <1992Dec2.111003.23102@jyu.fi> <1992Dec2.205330.10372@meaddata.com> Date: Fri, 4 Dec 1992 07:07:20 GMT Lines: 38 In ralpht@meaddata.com (Ralph W. Trickey) writes: >|> > >|> > I don't think that requiring total ordering would break any existing >|> >program, but it would break quite a few existing compilers. > >This language change that would slow down existing programs. Possibly >to the point where they no longer meet specifications. I consider this >breaking programs. Could someone do the net a great favour and check it? There's a lot of speculation but nobody has measured how severe the slow-down would be. >BTW, how did this thread start? The beginning has scrolled out of my >newsreader. I don't understand what total ordering would achieve. A total ordering would make it easier to build some common data structures. For example, a binary search tree needs some sort of comparison function. If you are only interested in finding a particular object in the tree (i.e., the actual ordering is irrelevant), comparing the addresses would work nicely. What you need in the search tree example is a total ordering for the duration of the program execution; it does not matter if the ordering is different the next time the program is executed. Note that some types of objects do not have a comparison function, and any existing comparison function may be expensive. I think the absense of a total ordering is a much greater problem in C++ than in C, because general purpose data structures are becoming much more common in the shape of templates. -- Dag -- Department of Automatic Control E-mail: dag@control.lth.se Lund Institute of Technology P. O. Box 118 Phone: +46 46-104287 S-221 00 Lund, SWEDEN Fax: +46 46-138118