NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/1729

Internet Message Format | 1996-08-05 | 1.8 KB

Path: mail2news.demon.co.uk!genesis.demon.co.uk
From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: Q: realloc->free?
Date: Tue, 16 Jan 96 16:19:37 GMT
Organization: none
Message-ID: <[e-mail]>
References: <4daa2e$[e-mail]> <4de8uv$[e-mail]>
Reply-To: [e-mail]
X-NNTP-Posting-Host: genesis.demon.co.uk
X-Newsreader: Demon Internet Simple News v1.27
X-Mail2News-Path: genesis.demon.co.uk

In article <4de8uv$[e-mail]>
           [e-mail] "Wildfire" writes:

>: b = realloc(a, 100);

...

>If you think about it, there is no need for realloc() to move the *start*
>of the allocated memory - it may need to make a link between the end of
>the original memory block and the start of an extension block, but that's
>different.

What do you mean by 'make a link'? The block of memory returned by realloc
must be contiguous so that, for example, you can treat it like an array
and access all elements using pointer arithmetic.

>So b is either going to be NULL or a.

Never assume in a program that b will equal a - it can and does change in
implementations even when the allocation size is being reduced (some
allcation schemes will allocate from different internal tables depending
on the allocation size, a realloc may require a shift from one table
to another on any change in size).

>realloc() does no free()ing, as far as I know, since the contents of
>memory are unchanged.

It releases unneeded space when you redude the allocation size and is
equivalent to free when the allocation size is zero.

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
-----------------------------------------