Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!uhccux!munnari.oz.au!mimir!hugin!augean!sirius!nt!levels!ccdn
From: CCDN@levels.sait.edu.au (DAVID NEWALL)
Newsgroups: comp.lang.c
Subject: Re: Obfuscated SWAP: not portable!
Message-ID: <1400@levels.sait.edu.au>
Date: 4 Sep 89 10:53:41 GMT
References: <784@skye.ed.ac.uk> <1267@levels.sait.edu.au> <149@cpsolv.UUCP>
Organization: Sth Australian Inst of Technology
Lines: 19

In article <149@cpsolv.UUCP>, rhg@cpsolv.UUCP (Richard H. Gumpertz) writes:
> The exchange of x and y that has been under discussion:
>     x ^= y ^= x ^= y
> is non-portable because it depends on right-to-left evaluation which is NOT
> specified in the C standard.

I think it is specified.  (Perhaps it depends on whose standard you follow?)

K&R I, page 19:
     "The line
        nl = nw = nc = 0;
    sets all three variables to zero.  This is not a special case, but a
    consequence of the fact that an assignment has a value and assignments
    associate right to left."

David Newall                     Phone:  +61 8 343 3160
Unix Systems Programmer          Fax:    +61 8 349 6939
Academic Computing Service       E-mail: ccdn@levels.sait.oz.au
SA Institute of Technology       Post:   The Levels, South Australia, 5095