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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: free a pointer and have it point to NULL |
| Date | 2014-04-22 14:53 -0700 |
| Organization | None to speak of |
| Message-ID | <lntx9lvxod.fsf@nuthaus.mib.org> (permalink) |
| References | <639a5283-8e4b-4f9a-aa7f-ef2c88174768@googlegroups.com> <bro63iFojnqU2@mid.uni-berlin.de> |
jt@toerring.de (Jens Thoms Toerring) writes:
> G G <gdotone@gmail.com> wrote:
>> memory allocated on the heap once freed should the pointer be assigned NULL?
>
> It can't hurt since any attempt to use the now invalid pointer
> again would lead to an immediate crash of the program. But then
> it depends a bit on circumstances: if the free() is at the end
> of a function and there's no chance that the pointer is acci-
> dentally used again, then there's not much good it will do.
> And, of course, each free() will have to be followed by
> another line of code, which can become tedious and make
> things a bit harder to read - unless you use a macro like
>
> #define safe_free( addr ) \
> do { \
> free( addr ); \
> addr = NULL; \
> } while ( 1 == 0 )
>
> instead of free() everywhere. I've done that in several cases
> where I felt the need to be paranoid;-)
"do { ... } while (0)" is the usual idiom for writing a macro that can
be used in a context requiring a statement; the "1 == 0" just seems
(mildly) obfuscated.
But when possible, it's usually better to write a macro that can be used
wherever an expression can appear. In this case:
#define safe_free(addr) ( free(addr), (addr) = NULL )
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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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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