From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lucio De Re <lucio@proxima.alt.za>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] manual suggestions and upas/fs bug
Message-ID: <20020917111727.U6063@cackle.proxima.alt.za>
References: <c881c5b5ee53a0c999a0f53343a87bf1@cs.cmu.edu> <3D8642ED.6BE57EE6@null.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <3D8642ED.6BE57EE6@null.net>; from Douglas A. Gwyn on Tue, Sep 17, 2002 at 08:47:45AM +0000
Date: Tue, 17 Sep 2002 11:17:27 +0200
Topicbox-Message-UUID: ed04c43a-eaca-11e9-9e20-41e7f4b1d025

On Tue, Sep 17, 2002 at 08:47:45AM +0000, Douglas A. Gwyn wrote:
> > >       if(n==0){
> > >               free(p);
> > >               p = malloc(n);
> > >       } else
> > >               p = realloc(p, n);
>
> p = realloc(p,n) is almost always a mistake.  If the allocation
> fails, the previous pointer value in p gets replaced by a null
> pointer value, so you lose the handle to the data that did not
> get extended (or, rarely, shrunk).

In other words,

	if (n==0)
		panic ("zero size");
	p = realloc(p, n);

is closer to the intent here.  Better still

	char *p0 = realloc(p, n);

	if (p0 == 0)
		panic ("realloc failed");
	p = p0;

would be a lot saner.  I forget the semantics, but realloc(p, n) need
not return p even if the reallocation succeeds.  What I don't know is
what happens to the space pointed to by p, I assume it's released.

++L