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From: sasrer@unx.sas.com (Rodney Radford)
Newsgroups: alt.folklore.urban,comp.lang.c,alt.folklore.computers
Subject: Re: Beautiful side-effects! (q = q++)
Message-ID: <1991Jun27.141220.9544@unx.sas.com>
Date: 27 Jun 91 14:12:20 GMT
References: <15520@exodus.Eng.Sun.COM> <1991Jun25.151408.1024@ux1.cso.uiuc.edu> <1991Jun26.154734.14439@dsuvax.uucp>
Organization: SAS Institute Inc.
Lines: 28

In article <1991Jun26.154734.14439@dsuvax.uucp> rolfe@dsuvax.uucp (Timothy J. Rolfe) writes:
>Beautify, beautiful side effect!!
>
>As it stands, "q = q++;" SHOULD leave q unchanged:  evaluating the
>right hand side we get a value (q BEFORE the increment).  That is
>the value that is supposed to go to the left hand side.  The question
>is WHEN the post-increment is done.

ANSII C says the behaviour of the above line is indetermined 
(ie: implementation dependent), and should be avoided in writing portable
C programs (to more that one machine, or more that one compiler, or 
possibly to different versions of the same compiler...).

The reason ANSII could not set a standard on this is that through the years
so many different versions of C existed and handled this differently. Also
should be avoided statements such as:

       array[i++] = i;

         --- or ---

       function(++k,k,k++)

These are just other examples of indeterminate side-effect expressions....
-- 
Rodney Radford          || Computer Graphics/Imaging
sasrer@unx.sas.com      || SAS Institute, Inc.
(919) 677-8000 x7703    || Cary, NC  27513