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Groups > comp.lang.c > #43836

Re: free a pointer and have it point to NULL

From James Kuyper <jameskuyper@verizon.net>
Newsgroups comp.lang.c
Subject Re: free a pointer and have it point to NULL
Date 2014-04-29 12:41 -0400
Organization Self
Message-ID <535FD623.5000200@verizon.net> (permalink)
References <639a5283-8e4b-4f9a-aa7f-ef2c88174768@googlegroups.com> <lny4yxvydz.fsf@nuthaus.mib.org> <ljo1b6$rba$1@news.albasani.net> <ljob8f$f8i$1@dont-email.me>

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On 04/29/2014 09:59 AM, James Kuyper wrote:
...
> ... There are real
> systems which have the ability to make blocks of memory switch from
> being valid to being invalid while a program is running, ...

I left out a key step: on such systems it is often the case that loading
an invalid into an address register is sufficient to cause your program
abort. Dereferencing the pointer isn't necessary. This is a safety
measure: the designers felt that any program written badly enough to
treat an invalid address as if were a valid one, is sufficiently
dangerous that it's safest to have a policy of stopping such programs as
soon as possible.

> ... and because of
> the clauses listed above, a fully conforming implementation of free()
> could have that effect.

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Thread

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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