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| From | Eric Sosman <esosman@comcast-dot-net.invalid> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Pointer Arithmetic & UB |
| Date | 2012-12-11 15:27 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <ka8501$545$1@dont-email.me> (permalink) |
| References | <ka559a$hdg$1@speranza.aioe.org> <50C621F9.8050705@verizon.net> <ka59e6$mq7$1@dont-email.me> <ka5vq2$lq6$1@blue-new.rahul.net> |
On 12/10/2012 7:46 PM, Edward A. Falk wrote:
> In article <ka59e6$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?
Assuming `i-j' in range, yes.
More on my colleague's tale: The code maintained a buffer
in which items of various sizes accumulated, and which drained
to disk when it got too full or too old. To decide whether a
newly-offered item would fit, the code did something like
itemEndPtr = nextBufferSpacePtr + itemSize;
if (itemEndPtr < bufferStart + bufferSize) ...
This worked as intended on all the other target systems, but
failed on AS/400. I suspect the failure had something to do
with the fact that the buffer was in a shared memory area, so
stepping off the end also meant stepping outside of mapped
address space; the problem might not have shown up with the
`auto' array in your example.
Still, perhaps a salutary lesson for the folks who still
believe "All the world's a VAX^H^H^Hx86^H^H^Hx64^H^H^H..."
--
Eric Sosman
esosman@comcast-dot-net.invalid
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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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