Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hpda!hpcupt1!hpisod2!decot
From: decot@hpisod2.HP.COM (Dave Decot)
Newsgroups: comp.lang.c
Subject: Re: Re: Teaching const: decoding declarations
Message-ID: <2550063@hpisod2.HP.COM>
Date: 10 Apr 88 05:54:40 GMT
References: <10203@steinmetz.steinmetz.ge.com>
Organization: Hewlett Packard, Cupertino
Lines: 30

> >	int * const a;
> >decodes as:
> >	a is a constant,
> >	a is a constant pointer,
> >	a is a constant pointer to an int.
> >		(i.e., a cannot be modified but *a can.)
> 
> Note that:
> 	 int a[1];
> decodes as:
>        a is a constant,
>        a is a constant pointer,
>        a is a constant pointer to an int.
> 	       (i.e., a cannot be modified but *a can.)
> 
> But there must (?) be some difference between the two.  How do you teach
> this?

The first declaration requests space for a pointer to an integer. If this is
a static declaration, the value is initialized to 0, so a can never point
to an object, and *a cannot be used to store a value.  Otherwise, the
(automatic) variable gets a garbage initial value which cannot be set to
anything useful.

The second declaration requests space for an array of one integer
(except when used to declare a formal parameter) and *a can immediately
be used to store an integer.

Dave Decot
hpda!decot