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Re: Pointer Arithmetic & UB

From Ken Brody <kenbrody@spamcop.net>
Newsgroups comp.lang.c
Subject Re: Pointer Arithmetic & UB
Date 2012-12-12 14:30 -0500
Organization A noiseless patient Spider
Message-ID <kaam0m$6cd$1@dont-email.me> (permalink)
References <ka559a$hdg$1@speranza.aioe.org> <50C621F9.8050705@verizon.net> <ka59e6$mq7$1@dont-email.me> <ka5vq2$lq6$1@blue-new.rahul.net>

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On 12/10/2012 7:46 PM, Edward A. Falk wrote:
> In article <ka59e6$mq7$1@dont-email.me>,
> Eric Sosman  <esosman@comcast-dot-net.invalid> wrote:
>>
>>      A colleague who did some work on IBM's AS/400 (they've
>> changed the name; I forget the new one) told me that simply
>> trying to calculate an out-of-range pointer yielded a null
>> pointer as a result.
>
> Heh; learn something new every day.  I never would have guessed
> that there was an actual architecture that would blow up with
> this construct.
>
> I assume that *(a+(i-j)) would be ok?

No.  There is no requirement that the value of "i-j" be calculated prior to 
adding it to "a".  (Check the numerous threads here involving using 
parentheses to "fix" UB in things involving such constructs as "i + (i++)".) 
  Operator precedence only guarantees how the expression is to be 
interpreted, not the actual order of evaluation.

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Thread

Pointer Arithmetic & UB Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-12-10 17:14 +0000
  Re: Pointer Arithmetic & UB "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-12-10 09:35 -0800
  Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 12:55 -0500
    Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-10 13:25 -0500
      Re: Pointer Arithmetic & UB falk@rahul.net (Edward A. Falk) - 2012-12-11 00:46 +0000
        Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 21:28 -0500
          Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:36 -0500
            Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-12 20:35 +0000
            Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-12 15:57 -0500
            Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-12 16:02 -0500
              Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-12 16:13 -0500
                Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-12 21:18 -0500
                Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-12 22:42 -0500
                Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:04 +0200
                Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-17 08:47 -0500
                Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 14:58 +0000
                Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-17 10:59 -0500
                Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 17:26 +0000
                Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-17 19:33 -0500
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-20 11:00 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-20 10:03 -0800
                Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-20 22:02 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-21 13:09 -0800
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-21 22:40 +0000
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-21 23:39 -0500
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-22 06:50 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-22 00:15 -0800
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-22 10:34 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-22 09:32 -0800
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-23 09:38 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-23 09:55 -0800
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-26 13:35 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 09:03 -0800
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-27 21:31 -0500
                Re: Pointer Arithmetic & UB Philip Lantz <prl@canterey.us> - 2012-12-28 01:55 -0800
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-29 13:43 -0800
                Re: Pointer Arithmetic & UB Philip Lantz <prl@canterey.us> - 2012-12-28 01:39 -0800
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-28 11:31 +0000
                Re: Pointer Arithmetic & UB Keith Thompson <kst-u@mib.org> - 2012-12-28 08:47 -0800
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-29 17:45 -0800
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-30 04:06 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-02 10:08 -0800
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-26 13:29 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 07:55 -0800
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 08:01 -0800
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-27 21:10 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-29 18:03 -0800
                Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-23 03:48 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-23 10:22 -0800
                Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-27 10:34 +0000
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 10:16 -0800
                Re: Pointer Arithmetic & UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-10 17:26 +0000
                Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-20 12:21 -0600
                Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-20 13:40 -0500
                Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-20 13:32 -0600
                Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-20 14:58 -0500
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-20 21:54 +0000
                Re: Pointer Arithmetic & UB Lanarcam <lanarcam1@yahoo.fr> - 2012-12-20 19:49 +0100
                Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-21 02:38 +0200
                Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-21 14:33 -0500
                Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-21 03:18 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-21 13:16 -0800
                Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-21 17:57 -0500
                Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-21 23:52 +0000
                Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-21 19:47 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-21 22:54 -0800
                Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-22 03:31 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-22 09:16 -0800
                Re: Pointer Arithmetic & UB Shao Miller <sha0.miller@gmail.com> - 2012-12-24 04:23 -0500
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-27 11:07 -0800
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 02:33 -0800
                Re: Pointer Arithmetic & UB Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 02:18 -0800
        Re: Pointer Arithmetic & UB Noob <root@127.0.0.1> - 2012-12-11 11:36 +0100
          Re: Pointer Arithmetic & UB "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-12-11 10:00 -0800
            Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:11 +0200
        Re: Pointer Arithmetic & UB Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-12-11 15:27 -0500
          Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-11 21:09 +0000
        Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:30 -0500
          Re: Pointer Arithmetic & UB Keith Thompson <kst-u@mib.org> - 2012-12-12 11:42 -0800
          Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 17:12 -0500
          Re: Pointer Arithmetic & UB Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:16 +0200
  Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 12:04 -0800
    Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 15:29 -0500
      Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 12:44 -0800
        Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 12:47 -0800
          Re: Pointer Arithmetic & UB James Kuyper <jameskuyper@verizon.net> - 2012-12-10 16:02 -0500
            Re: Pointer Arithmetic & UB Prathamesh Kulkarni <bilbotheelffriend@gmail.com> - 2012-12-10 13:08 -0800
              Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:26 -0500
            Re: Pointer Arithmetic & UB Greg Martin <greg@softsprocket.com> - 2012-12-10 14:55 -0800
        Re: Pointer Arithmetic & UB Sjouke Burry <s@b> - 2012-12-10 21:18 +0000
        Re: Pointer Arithmetic & UB falk@rahul.net (Edward A. Falk) - 2012-12-11 00:48 +0000
      Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-10 21:01 +0000
      Re: Pointer Arithmetic & UB Ken Brody <kenbrody@spamcop.net> - 2012-12-12 14:24 -0500
        Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-12 14:34 -0600
        Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-12 20:45 +0000
          Re: Pointer Arithmetic & UB Robert Wessel <robertwessel2@yahoo.com> - 2012-12-12 15:29 -0600
            Re: Pointer Arithmetic & UB glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-13 02:02 +0000
        Re: Pointer Arithmetic & UB Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-12-17 05:57 -0800
    Re: Pointer Arithmetic & UB pete <pfiland@mindspring.com> - 2012-12-10 20:20 -0500

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