Newsgroups: comp.lang.c
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Contiguous Arrays
Message-ID: <1989Feb23.165715.9013@utzoo.uucp>
Organization: U of Toronto Zoology
References: <2508@ssc-vax.UUCP> <8943@alice.UUCP> <1828@valhalla.ee.rochester.edu> <1989Feb22.171441.7957@utzoo.uucp> <1831@valhalla.ee.rochester.edu>
Date: Thu, 23 Feb 89 16:57:15 GMT

In article <1831@valhalla.ee.rochester.edu> badri@valhalla.ee.rochester.edu (Badri Lokanathan) writes:
>My argument is, since x is an independent variable (a pointer, but
>still a variable,) there is no way of checking any array bounds.
>Thus in order for consistency with the definition of pointer
>arithmetic,
>x -= i; x += i;
>should result in the original value of x (provided the resulting
>intermediate values are within pointer ranges.)

Exactly -- provided the intermediate values do not cause an overflow.
ON SOME MACHINES THEY CAN.  It is not true that all machines have a
single linear homogenous address space.  Some have it broken up into
pieces, and bad things can happen if your pointer arithmetic goes over
the edge of a piece.

>Further, the + and - operations group left to right and are
>associative...

In the absence of overflow.
-- 
The Earth is our mother;       |     Henry Spencer at U of Toronto Zoology
our nine months are up.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu