Re: C is not a low level language

From	Richard Heathfield <rjh@cpax.org.uk>
Newsgroups	comp.lang.c, comp.programming, comp.sys.raspberry-pi
Subject	Re: C is not a low level language
Date	2019-02-24 19:26 +0000
Organization	Fix this later
Message-ID	<q4ur5a$v7v$1@dont-email.me> (permalink)
References	(7 earlier) <q4ua9h$j2g$1@dont-email.me> <q4ucji$vqc$1@dont-email.me> <q4ug9o$q6j$1@gioia.aioe.org> <q4un6q$5bo$1@dont-email.me> <q4upp6$5k2$1@gioia.aioe.org>

Cross-posted to 3 groups.

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On 24/02/2019 19:02, R.Wieser wrote:
> Richard,
> 
>> Okay, so that's so obvious a retort that I have to deduce you meant
>> something else, but I don't know what. Care to explain for the benefit of
>> my befuddled grey cells?
> 
> You responded to a post in which was explained that "strncpy" could be
> dangerous because you could fill the buffer out with a too-long string,
> leaving it without a terminator.

With you so far...

> The defensive method would be to stop
> copying before you overwrite the last byte in the target buffer - thereby
> making sure that whatever may happen, the buffer will hold a zero-terminated
> string.

But my code protected against that possibility by obtaining the length 
of the source string including terminator: len = strlen(src) + 1; and 
then allocating exactly that amount of memory via malloc, and then using 
memcpy to copy exactly that many bytes. The only way this could break 
would be if the source string grew between two consecutive lines of code 
that did not grow that string. This *could* happen in a multi-threaded 
context, of course, but in a multi-threaded context one would take 
additional precautions to ensure that only one thread had access to the 
string at the point of duplication.

OR... I'm missing something! :-)

> 
>> Reporting an error is certainly preferable to undefined behaviour, but I
>> would prefer to grab the data - all of it - if that's possible and
>> reasonable.
> 
> I went along with you upto-and-including the "- all of it -".  The latter
> part ?  Not so much.  Not even humans are really capable of acting
> (correctly!) on partial messages, let alone un-imaginative programs.  And
> boy, can they do a lot of damage ...

Well, if it's impossible it's impossible and that's all there is to it. 
And I gave an example of a scenario in which an unreasonable amount of 
data could be deliberately thrown at the program with the express intent 
of consuming all available memory. If these circumstances are at all 
likely, it seems to me that it is better to protect against them than to 
succumb blindly to them.

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within

Thread

Re: C is not a low level language "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-02-24 12:40 +0800
  Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 05:16 +0000
    Re: C is not a low level language "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-02-24 13:20 +0800
      Re: C is not a low level language "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-02-24 13:24 +0800
      Re: C is not a low level language "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-02-24 19:45 +0800
      Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 13:09 +0000
        Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 14:38 +0000
          Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 15:18 +0000
            Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-24 17:21 +0100
              Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 17:43 +0000
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-24 20:17 +0100
              Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 18:19 +0000
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-24 20:02 +0100
                Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 19:26 +0000
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-24 21:36 +0100
                Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 20:47 +0000
                Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 21:10 +0000
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 08:25 +0100
                Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-25 12:24 +0000
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 17:04 +0100
                Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-25 16:52 +0000
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-24 17:59 -0800
                Re: C is not a low level language "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-25 08:46 +0100
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 09:36 +0100
                Re: C is not a low level language "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-25 10:13 +0100
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-26 09:56 +0100
                Re: C is not a low level language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-02-25 14:12 +0000
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 12:20 +0000
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-25 13:36 -0800
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 10:29 +0200
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 09:41 +0100
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 10:55 +0200
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 10:24 +0100
                Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 21:03 +0000
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 08:58 +0100
                Re: C is not a low level language "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-25 09:40 +0100
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 10:01 +0100
              Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-24 12:55 -0800
                Re: C is not a low level language "R.Wieser" <address@not.available> - 2019-02-25 08:31 +0100
            Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 17:42 +0000
              Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 18:19 +0000
            Re: C is not a low level language Bill Findlay <findlaybill@blueyonder.co.uk> - 2019-02-24 17:56 +0000
              Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-24 18:23 +0000
                Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 20:58 +0000
              Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 20:52 +0000
                Re: C is not a low level language Bill Findlay <findlaybill@blueyonder.co.uk> - 2019-02-25 16:31 +0000
              Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-25 14:01 -0800
                Re: C is not a low level language scott@slp53.sl.home (Scott Lurndal) - 2019-02-25 23:04 +0000
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-25 15:53 -0800
                Re: C is not a low level language Bill Findlay <findlaybill@blueyonder.co.uk> - 2019-02-28 16:07 +0000
              Re: C is not a low level language Björn Lundin <b.f.lundin@gmail.com> - 2019-02-25 20:50 +0100
                Re: C is not a low level language Bill Findlay <findlaybill@blueyonder.co.uk> - 2019-02-28 16:04 +0000
                Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-28 16:25 +0000
                Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-28 11:56 -0500
                Re: C is not a low level language "NY" <me@privacy.net> - 2019-02-28 19:45 +0000
              Re: C is not a low level language Bart <bc@freeuk.com> - 2019-02-25 17:55 +0000
                Re: C is not a low level language Bill Findlay <findlaybill@blueyonder.co.uk> - 2019-02-28 16:03 +0000
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-28 11:25 -0800
                Re: C is not a low level language Bart <bc@freeuk.com> - 2019-02-28 19:30 +0000
          Re: C is not a low level language Jasen Betts <jasen@xnet.co.nz> - 2019-02-24 20:47 +0000
            Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 21:29 +0000
              Re: C is not a low level language Jasen Betts <jasen@xnet.co.nz> - 2019-02-25 20:16 +0000
      Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-24 12:53 -0800
      Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 09:49 +0200
    Re: C is not a low level language Björn Lundin <b.f.lundin@gmail.com> - 2019-02-25 21:07 +0100
      Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 22:59 +0000
        Re: C is not a low level language Björn Lundin <b.f.lundin@gmail.com> - 2019-02-26 09:57 +0100
          Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-26 09:59 +0000
  Re: C is not a low level language Eric Stevens <eric.stevens@sum.co.nz> - 2019-02-24 19:54 +1300
    Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-24 07:56 +0000
      Re: C is not a low level language Eric Stevens <eric.stevens@sum.co.nz> - 2019-02-24 21:58 +1300
        Re: C is not a low level language "A. Dumas" <alexandre@dumas.fr.invalid> - 2019-02-24 10:57 +0100
        Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-24 10:13 +0000
        Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 10:47 +0000
          Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-24 08:48 -0500
            Re: C is not a low level language The Natural Philosopher <tnp@invalid.invalid> - 2019-02-24 14:42 +0000
            Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 07:15 +0000
              Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-25 09:25 -0500
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 15:03 +0000
                Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-25 12:10 -0500
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 17:58 +0000
                Re: C is not a low level language Axel Berger <Spam@Berger-Odenthal.De> - 2019-02-25 17:44 +0100
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 19:18 +0200
            Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 10:35 +0200
              Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-25 10:44 +0000
                Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-02-25 12:29 +0000
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 14:26 +0000
                Re: C is not a low level language "NY" <me@privacy.net> - 2019-02-25 17:08 +0000
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 20:08 +0200
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 18:00 +0000
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-27 22:37 -0800
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-28 02:25 -0800
                Re: C is not a low level language Diesel <nobody@haph.org> - 2019-03-05 04:29 +0000
              Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 12:27 +0000
              Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-25 09:36 -0500
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 15:05 +0000
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 19:20 +0200
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-25 23:02 +0000
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-26 06:52 +0000
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-26 12:41 +0200
                Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-26 12:20 +0000
                Re: C is not a low level language David Brown <david.brown@hesbynett.no> - 2019-02-26 14:01 +0100
                Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-26 08:48 -0500
                Re: C is not a low level language Björn Lundin <b.f.lundin@gmail.com> - 2019-02-26 19:20 +0100
              Re: C is not a low level language Wolf K <wolfmac@sympatico.ca> - 2019-02-25 10:04 -0500
        Re: C is not a low level language lonelydad <lonelydad58@gmail.com> - 2019-02-24 14:44 +0000
        Re: C is not a low level language "U-laptop\\Norah" <Norah@laptop.i-did-not-set--mail-host-address--so-tickle-me> - 2019-02-27 16:16 -0600
          Re: C is not a low level language Eric Stevens <eric.stevens@sum.co.nz> - 2019-03-01 12:12 +1300
            Re: C is not a low level language Richard Heathfield <rjh@cpax.org.uk> - 2019-03-01 00:19 +0000
      Re: C is not a low level language Gene Wirchenko <genew@telus.net> - 2019-02-24 19:59 -0800
        Re: C is not a low level language Bill Findlay <findlaybill@blueyonder.co.uk> - 2019-02-25 16:10 +0000
        Re: C is not a low level language Björn Lundin <b.f.lundin@gmail.com> - 2019-02-25 21:02 +0100
          Re: C is not a low level language Lars Enderin <lars.enderin@telia.com> - 2019-02-26 00:37 +0100
            Re: C is not a low level language Wolf K <wolfmac@sympatico.ca> - 2019-02-25 19:09 -0500
            Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-26 06:52 +0000
    Re: C is not a low level language T <T@invalid.invalid> - 2019-02-24 00:30 -0800
      Re: C is not a low level language T <T@invalid.invalid> - 2019-02-24 00:31 -0800
      Re: C is not a low level language Ahem A Rivet's Shot <steveo@eircom.net> - 2019-02-24 10:16 +0000
    Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-24 11:22 +0000
      Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-24 08:51 -0500
        Re: C is not a low level language pyotr filipivich <phamp@mindspring.com> - 2019-02-24 07:20 -0800
          Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-24 15:35 +0000
            Re: C is not a low level language "Mayayana" <mayayana@invalid.nospam> - 2019-02-24 11:05 -0500
            Re: C is not a low level language pyotr filipivich <phamp@mindspring.com> - 2019-02-24 14:39 -0800
              Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-24 19:11 -0800
              Re: C is not a low level language Wolf K <wolfmac@sympatico.ca> - 2019-02-25 09:41 -0500
                Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-25 14:53 +0000
                Re: C is not a low level language Wolf K <wolfmac@sympatico.ca> - 2019-02-25 10:19 -0500
                Re: C is not a low level language David Brown <david.brown@hesbynett.no> - 2019-02-25 16:38 +0100
                Re: C is not a low level language Wolf K <wolfmac@sympatico.ca> - 2019-02-25 11:20 -0500
                Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-25 17:49 +0000
                Re: C is not a low level language David Brown <david.brown@hesbynett.no> - 2019-02-26 09:18 +0100
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 12:17 -0500
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 20:25 +0200
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 13:40 -0500
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-26 12:45 +0200
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-26 08:02 -0500
                Re: C is not a low level language Wolf K <wolfmac@sympatico.ca> - 2019-02-26 09:11 -0500
                Re: C is not a low level language Diesel <nobody@haph.org> - 2019-03-05 04:29 +0000
                Re: C is not a low level language David Brown <david.brown@hesbynett.no> - 2019-02-26 09:23 +0100
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-26 08:02 -0500
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-26 17:57 +0200
                Re: C is not a low level language Diesel <nobody@haph.org> - 2019-03-05 04:29 +0000
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 17:42 -0500
                Re: C is not a low level language Bart <bc@freeuk.com> - 2019-02-25 22:33 +0000
                Re: C is not a low level language David Brown <david.brown@hesbynett.no> - 2019-02-26 09:30 +0100
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 12:17 -0500
                Re: C is not a low level language Keith Thompson <kst-u@mib.org> - 2019-02-25 13:52 -0800
                Re: C is not a low level language "NY" <me@privacy.net> - 2019-02-25 15:20 +0000
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 12:17 -0500
                Re: C is not a low level language Bart <bc@freeuk.com> - 2019-02-25 18:47 +0000
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 13:50 -0500
                Re: C is not a low level language Bart <bc@freeuk.com> - 2019-02-25 18:59 +0000
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-25 20:15 +0200
                Re: C is not a low level language scott@slp53.sl.home (Scott Lurndal) - 2019-02-25 18:38 +0000
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-26 12:49 +0200
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 13:40 -0500
                Re: C is not a low level language Wouter Verhelst <w@uter.be> - 2019-02-26 12:55 +0200
                Re: C is not a low level language scott@slp53.sl.home (Scott Lurndal) - 2019-02-26 16:29 +0000
                Re: C is not a low level language Diesel <nobody@haph.org> - 2019-03-05 04:29 +0000
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-03-04 23:43 -0500
                Re: C is not a low level language "NY" <me@privacy.net> - 2019-02-25 18:16 +0000
                Re: C is not a low level language "NY" <me@privacy.net> - 2019-02-25 17:44 +0000
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 13:05 -0500
                Re: C is not a low level language Robert Wessel <robertwessel2@yahoo.com> - 2019-02-26 00:51 -0600
                Re: C is not a low level language "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-26 10:58 +0100
                Re: C is not a low level language Robert Wessel <robertwessel2@yahoo.com> - 2019-02-26 10:53 -0600
                Re: C is not a low level language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-02-26 17:49 +0000
                Re: C is not a low level language scott@slp53.sl.home (Scott Lurndal) - 2019-02-26 18:11 +0000
                Re: C is not a low level language Bart <bc@freeuk.com> - 2019-02-26 18:24 +0000
                Re: C is not a low level language "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-26 19:24 +0100
                Re: C is not a low level language "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-02-26 19:44 +0100
                Re: C is not a low level language nobody@example.org (Scott) - 2019-02-26 06:33 +0000
                Re: C is not a low level language nospam <nospam@nospam.invalid> - 2019-02-25 12:17 -0500
        Re: C is not a low level language Gene Wirchenko <genew@telus.net> - 2019-02-24 20:03 -0800
      Re: C is not a low level language pyotr filipivich <phamp@mindspring.com> - 2019-02-24 14:56 -0800
  Re: C is not a low level language Jasen Betts <jasen@xnet.co.nz> - 2019-02-24 20:43 +0000
    Re: C is not a low level language "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-02-25 14:14 +0800
      Re: C is not a low level language "J. P. Gilliver (John)" <G6JPG-255@255soft.uk> - 2019-02-25 10:45 +0000
        Re: C is not a low level language "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-02-25 19:04 +0800

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