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From: guy@sun.uucp (Guy Harris)
Newsgroups: net.lang.c
Subject: Re: c programming style
Message-ID: <2461@sun.uucp>
Date: Sun, 21-Jul-85 17:45:25 EDT
Article-I.D.: sun.2461
Posted: Sun Jul 21 17:45:25 1985
Date-Received: Wed, 24-Jul-85 06:28:28 EDT
References: <13@brl-tgr.ARPA> <1303@uwmacc.UUCP>
Organization: Sun Microsystems, Inc.
Lines: 32

> I submit that equating a globally recognized set of constants (i.e. the
> set of integers) with values that differ depending on whatever program
> variable happens to be nearest to them is guaranteed to be misleading.

What changed is not the values of the integers but the operation implied by
the "+" operator.  pointer + N causes the pointer to point to the
object (of the type the pointer's type is derived from) N objects (*NOT* N
machine storage units) further into the array that "pointer" is assumed to
point to a member of.  This is a bit subtle, but a lot easier to understand
if you realize that pointers are NOT integers but abstract cookies referring
to objects in memory.  Most of the confusion stems from a too low-level
mental model of C; people think of pointers as integers indexing a memory
considered as a sequence of machine storage units instead of as the
aforementioned abstract cookies.

The fact that so many people have trouble with this is either because:

	1) The low-level model of memory and pointers is so ingrained into
	   programmer's consciousnesses that trying to make pointers a more
	   abstract model is doomed to failure

or

	2) C just hasn't been taught correctly - the instruction gives a
	   lower-level model than is appropriate.

The solution to 1) is to rip out pointer arithmetic, use arrays instead, and
have all C compilers do strength reduction to generate multiplication-free
code.  The solution to 2) is to avoid giving the impression that C is a
structured assembly language.

	Guy Harris