Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!mcvax!ukc!its63b!hwcs!hwee!hmc From: hmc@hwee.UUCP (Hugh Conner) Newsgroups: comp.lang.c Subject: Re: Style [++i vs i++] Message-ID: <259@hwee.UUCP> Date: Tue, 14-Jul-87 04:54:11 EDT Article-I.D.: hwee.259 Posted: Tue Jul 14 04:54:11 1987 Date-Received: Fri, 17-Jul-87 05:58:04 EDT References: <17310@amdcad.AMD.COM> <246@hubcap.UUCP> Reply-To: hmc@hwee (Hugh Conner) Organization: Heriot-Watt University, Electrical Eng. Lines: 30 In article <246@hubcap.UUCP> beede@hubcap.UUCP (Mike Beede) writes: >in article <17310@amdcad.AMD.COM>, tim@amdcad.AMD.COM (Tim Olson) says: >> >> [ question: use ++i or i++ when only side-effect is desired ] >> >There is no reason a compiler needs to generate code differently for i++; and >++i; if that is the entire expression (and statement). > As I remember the original PDP-11 C compiler did treat the two cases differently. This was because the PDP had an autoincrement addressing mode of the form Op (Rn)+ which meant that register n was used as a pointer to a location and then incremented. This made i++ more efficient that ++i since it could make use of this mode. Similarly the autodecrement mode on the PDP took the form Op -(Rn) thus making --i more efficient than i--. This is probably no longer true of many (or all) systems, but it still affects the way I tend to write programs. -- + "Who are all these people in my office anyway?" + + + + Hugh M. Conner hmc@ee.hw.ac.uk +