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From: perry@ccssrv.UUCP (Perry Hutchison)
Newsgroups: comp.lang.c
Subject: Re: register variable???
Message-ID: <615@ccssrv.UUCP>
Date: 13 Sep 89 01:54:50 GMT
References: <30585@srcsip.UUCP> <19487@mimsy.UUCP>
Reply-To: perry@ccssrv.UUCP (Perry Hutchison)
Organization: Control-C Software, Inc., Beaverton, OR
Lines: 21

In article <19487@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:

> In article <30585@srcsip.UUCP> sklee@pompeii.SRC.Honeywell.COM (Sungkee Lee)
> writes:
> >  while (i < 4)  list[i] = list[++i];
> 
> USE LINT!!!!!
> 
> Sheesh.

Provided he has it on his system and understands the (frequently cryptic)
messages it produces.  Let's answer the fellow's question:

The assignment produces "undefined results" because there is no guarantee
as to when "side effects" (like ++) happen.  According to the definition
of prefix ++, the right-hand operand of = must use the incremented value of
i as the subscript; however the left-hand operand may evaluate the address
into which the assignment will take place either before or after the right-
hand expression stores the incremented value into i.  It appears that, in
this implementation, that decision is different depending on whether i is
a register variable.