Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!amdcad!light!bvs
From: bvs@light.uucp (Bakul Shah)
Newsgroups: comp.lang.c
Subject: const pointers
Message-ID: <1988Apr4.082020.1687@light.uucp>
Date: 4 Apr 88 16:20:18 GMT
References: <1988Apr3.013733.28401@utzoo.uucp>
Reply-To: bvs@light.UUCP (Bakul Shah)
Organization: Light Systems, Mountain View, CA
Lines: 30
Summary: <type> * const <object> has a well defined and useful meaning

In article <1988Apr3.013733.28401@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>
>               ...              const on a pointer does not mean that the
>thing pointed to is constant, just that attempts to modify it through that
							    ^^
>pointer are illegal.  (If this double meaning of const strikes you as less
>than ideal, you're in good company.)

Huh?  If by `it' you mean the object pointed to by the const pointer,
your intepretation seems wrong (or I have misunderstood you or the
draft).

To manipulate an object at a fixed known location, we used to have to
play games like
	#define ioreg   ((long *)0x4000004)
Instead, now we can say
	long * const ioreg = (long *)0x4000004;
As I understand it, here `ioreg' is a const and `*ioreg' is a variable.

In both cases
	*ioreg = 5;
is legal, and
	ioreg = (long *)0x1234;
is flagged by the compiler as illegal, which is exactly the effect one
wants.

I don't see a double meaning; perhaps you'd like to elaborate?
-- 
Bakul Shah

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