Re: UB of memcpy(NULL, NULL, 0)

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From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: UB of memcpy(NULL, NULL, 0)
Date	Sun, 23 Oct 2016 12:22:57 -0700
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Lőrinczy Zsigmond <nospam@for.me> writes:
> How to resolve this? It is not possible,
> it cannot be resolved;
> the standard is out, so libc-implementors
> and compiler-writer are allowed to do
> tricks I don't like, but are legal
> according to the standard.
> (see the original post)
>
> Also there is no point in changing the standard,
> or fix this in later versions,
> it would only increase the chaos.

When you post a followup, please retain enough quoted context
from the parent article, including attribution lines, so that your
followup makes sense.  I see you're using Thunderbird; I'm reasonably
sure it will do this for you.

What exactly needs to be "resolved"?  The standard is clear that
the behavior of memcpy(NULL, NULL, 0) is undefined.  If you want
to assume that it's a harmless no-op, you're free to do so; your
implementation might support that assumption, but the standard
doesn't.  If you're writing an implementation, you can make it
behave as a harmless no-op; that's entirely consistent with what
the standard requires.  If you want a future edition of the standard
to define the behavior, you can certainly advocate such a change.

Meanwhile, any remaining problems can be avoided simply by *not*
passing null pointers to memcpy().  The effort needed to do this is
nonexistent in most cases, and minimal in all other cases.

-- 
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"

Thread

UB of memcpy(NULL, NULL, 0) Noob <root@127.0.0.1> - 2016-10-13 12:42 +0200
  Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-13 11:55 +0100
    Re: UB of memcpy(NULL, NULL, 0) Noob <root@127.0.0.1> - 2016-10-13 13:09 +0200
      Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-13 12:22 +0100
        Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-13 12:22 -0700
          Re: UB of memcpy(NULL, NULL, 0) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-10-13 12:32 -0700
            Re: UB of memcpy(NULL, NULL, 0) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-10-13 12:34 -0700
    Re: UB of memcpy(NULL, NULL, 0) Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-10-13 08:24 -0600
      Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-13 16:22 +0100
      Re: UB of memcpy(NULL, NULL, 0) Noob <root@127.0.0.1> - 2016-10-13 17:49 +0200
        Re: UB of memcpy(NULL, NULL, 0) Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-10-13 12:02 -0600
  Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-15 20:56 +0200
    Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-15 12:52 -0700
    Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-15 15:55 -0400
    Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-15 13:41 -0700
      Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-16 11:17 +0200
        Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-16 10:26 +0100
        Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-16 09:55 +0000
          Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-16 08:44 -0400
            Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 10:06 +0200
              Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-17 09:06 -0400
                Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 16:29 +0200
                Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-17 17:05 -0400
                Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-18 11:19 +0200
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 08:04 -0700
                Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-18 16:27 -0400
            Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 08:59 -0700
              Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-17 11:21 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 13:42 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-17 14:46 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 15:52 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-17 16:43 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 08:00 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-18 09:14 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 09:43 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-18 11:31 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 12:49 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-18 12:03 -0700
              Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-17 17:06 -0400
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 14:55 -0700
        Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-16 11:23 -0700
      Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 08:49 -0700
        Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-18 16:54 +0000
          Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 11:09 -0700
            Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-23 13:24 +0000
              Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 09:28 -0700
              Re: UB of memcpy(NULL, NULL, 0) <william@wilbur.25thandClement.com> - 2016-10-29 11:32 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-29 14:12 -0700
    Re: UB of memcpy(NULL, NULL, 0) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-15 22:00 +0100
      Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-16 02:51 -0700
        Re: UB of memcpy(NULL, NULL, 0) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-16 11:20 +0100
          Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-16 04:14 -0700
            Re: UB of memcpy(NULL, NULL, 0) BartC <bc@freeuk.com> - 2016-10-16 12:22 +0100
            Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-16 13:01 +0100
              Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-16 05:29 -0700
                Re: UB of memcpy(NULL, NULL, 0) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-16 20:47 +0100
                Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-17 02:08 -0700
                Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 10:24 +0200
                Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-17 08:05 -0700
                Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 17:25 +0200
  Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-17 17:08 +0200
    Re: UB of memcpy(NULL, NULL, 0) Lorinczy Zsigmond <zsiga@nospam.for.me> - 2016-10-21 12:46 +0200
      Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-21 08:06 -0700
        Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-21 18:30 +0200
          Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-21 09:34 -0700
            Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-22 07:42 +0200
              Re: UB of memcpy(NULL, NULL, 0) James Kuyper <jameskuyper@verizon.net> - 2016-10-22 10:31 -0400
                Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-22 17:49 +0200
                Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-22 13:43 -0700
                Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-23 07:47 +0200
                Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-23 11:07 -0400
                Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-23 17:45 +0200
                Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-23 12:16 -0400
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 07:38 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 08:38 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 09:44 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-23 12:22 -0700
                Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-23 13:37 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-23 14:15 -0700
                Re: UB of memcpy(NULL, NULL, 0) Ike Naar <ike@iceland.freeshell.org> - 2016-10-24 06:11 +0000
                Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-24 00:58 -0700
                Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-23 14:07 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 07:48 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 08:40 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 10:03 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 12:06 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 13:36 -0700
                Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 13:57 -0700
                Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-24 14:16 -0700
                Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 17:23 -0700
                Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-25 07:57 -0700
                Re: UB of memcpy(NULL, NULL, 0) James Kuyper <jameskuyper@verizon.net> - 2016-10-22 18:23 -0400
                Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-23 10:44 -0400
                Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-23 16:24 +0100
                Re: Verbing Noob <root@127.0.0.1> - 2016-10-23 18:02 +0200
        Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-23 13:26 +0000
          Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-23 07:40 -0700
      Re: UB of memcpy(NULL, NULL, 0) asetofsymbols@gmail.com - 2016-10-21 23:56 -0700
        Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-22 12:21 +0200
          Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-22 16:33 -0700

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