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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: free a pointer and have it point to NULL |
| Date | 2014-04-22 17:32 -0400 |
| Organization | Self |
| Message-ID | <5356E006.3040900@verizon.net> (permalink) |
| References | <639a5283-8e4b-4f9a-aa7f-ef2c88174768@googlegroups.com> |
On 04/22/2014 05:22 PM, G G wrote:
> memory allocated on the heap once freed should the pointer be assigned NULL?
Only if there's a danger of the pointer being used again after being
free()'d. Even then, it's only useful if other code, elsewhere, checks
if(p) before trying to dereference p. Finally, if there are multiple
saved pointers, all pointing into the same block of allocated memory,
setting one of those pointers to be null won't help avoid problems with
any of the other pointers. They must all be protected by if(p).
I often use the following approach, which removes all need for nulling
out the free()'d pointer:
{
int *p = malloc(num_elements*sizeof *p);
if(p==NULL)
{
// Error handling
}
else
{
// Code which uses *p
free(p);
}
// Key point: *p is not used anywhere in this section
}
Since the lifetime of 'p' ends immediately after free(p), there's no
need to write "p = NULL;". This approach cannot be used if the malloc()
and free() must occur in different functions, or at very different
levels within the same function.
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free a pointer and have it point to NULL G G <gdotone@gmail.com> - 2014-04-22 14:22 -0700
Re: free a pointer and have it point to NULL James Kuyper <jameskuyper@verizon.net> - 2014-04-22 17:32 -0400
Re: free a pointer and have it point to NULL G G <gdotone@gmail.com> - 2014-04-22 14:36 -0700
Re: free a pointer and have it point to NULL Keith Thompson <kst-u@mib.org> - 2014-04-22 14:37 -0700
Re: free a pointer and have it point to NULL Johannes Bauer <dfnsonfsduifb@gmx.de> - 2014-04-29 13:10 +0200
Re: free a pointer and have it point to NULL Richard <rgrdev_@gmail.com> - 2014-04-29 13:14 +0200
Re: free a pointer and have it point to NULL Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-29 13:19 +0100
Re: free a pointer and have it point to NULL Kaz Kylheku <kaz@kylheku.com> - 2014-04-29 13:57 +0000
Re: free a pointer and have it point to NULL Kaz Kylheku <kaz@kylheku.com> - 2014-04-29 13:43 +0000
Re: free a pointer and have it point to NULL James Kuyper <jameskuyper@verizon.net> - 2014-04-29 09:59 -0400
Re: free a pointer and have it point to NULL Keith Thompson <kst-u@mib.org> - 2014-04-29 07:58 -0700
Re: free a pointer and have it point to NULL Keith Thompson <kst-u@mib.org> - 2014-04-29 11:50 -0700
Re: free a pointer and have it point to NULL James Kuyper <jameskuyper@verizon.net> - 2014-04-29 15:47 -0400
Re: free a pointer and have it point to NULL James Kuyper <jameskuyper@verizon.net> - 2014-04-29 12:41 -0400
Re: free a pointer and have it point to NULL Robert Wessel <robertwessel2@yahoo.com> - 2014-04-29 13:15 -0500
Re: free a pointer and have it point to NULL glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-29 21:29 +0000
Re: free a pointer and have it point to NULL glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-29 15:26 +0000
Re: free a pointer and have it point to NULL jt@toerring.de (Jens Thoms Toerring) - 2014-04-22 21:43 +0000
Re: free a pointer and have it point to NULL Keith Thompson <kst-u@mib.org> - 2014-04-22 14:53 -0700
Re: free a pointer and have it point to NULL Öö Tiib <ootiib@hot.ee> - 2014-04-24 00:38 -0700
Re: free a pointer and have it point to NULL James Kuyper <jameskuyper@verizon.net> - 2014-04-24 07:52 -0400
Re: free a pointer and have it point to NULL <william@wilbur.25thandClement.com> - 2014-04-24 16:13 -0700
Re: free a pointer and have it point to NULL Ian Collins <ian-news@hotmail.com> - 2014-04-25 12:02 +1200
Re: free a pointer and have it point to NULL <william@wilbur.25thandClement.com> - 2014-04-24 22:03 -0700
Re: free a pointer and have it point to NULL Ian Collins <ian-news@hotmail.com> - 2014-04-25 17:22 +1200
Re: free a pointer and have it point to NULL <william@wilbur.25thandClement.com> - 2014-04-24 23:00 -0700
Re: free a pointer and have it point to NULL Öö Tiib <ootiib@hot.ee> - 2014-04-27 08:32 -0700
Re: free a pointer and have it point to NULL Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2014-04-22 16:19 -0600
Re: free a pointer and have it point to NULL Kaz Kylheku <kaz@kylheku.com> - 2014-04-22 22:41 +0000
Re: free a pointer and have it point to NULL Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2014-04-22 18:17 -0600
Re: free a pointer and have it point to NULL Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2014-04-24 08:48 -0600
non-NULL pointers which have the value 0 (Was: Re: free a pointer and have it point to NULL) Andrew Cooper <root@127.0.0.1> - 2014-04-23 03:28 +0100
Re: non-NULL pointers which have the value 0 (Was: Re: free a pointer and have it point to NULL) Kaz Kylheku <kaz@kylheku.com> - 2014-04-23 04:37 +0000
Re: non-NULL pointers which have the value 0 glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-23 06:14 +0000
Re: free a pointer and have it point to NULL Kaz Kylheku <kaz@kylheku.com> - 2014-04-22 22:18 +0000
Re: free a pointer and have it point to NULL Michael Angelo Ravera <maravera@prodigy.net> - 2014-05-03 01:00 -0700
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