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Re: UB or not UB? was: On Undefined Behavior

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: UB or not UB? was: On Undefined Behavior
Date 2026-01-12 12:03 -0800
Organization A noiseless patient Spider
Message-ID <86qzrulht3.fsf@linuxsc.com> (permalink)
References <10j6qdt$3q9n4$1@dont-email.me> <20260112162857.00003dd8@yahoo.com> <10k360j$2epre$1@dont-email.me> <20260112193652.000051d0@yahoo.com>

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Michael S <already5chosen@yahoo.com> writes:

> On Mon, 12 Jan 2026 08:03:31 -0800
> Andrey Tarasevich <noone@noone.net> wrote:
>
>> On Mon 1/12/2026 6:28 AM, Michael S wrote:
>>
>>> According to C Standard, access to p->table[4] in foo1() is UB.
>>> ...
>>> Now the question.
>>> What The Standard says about foo2() ? Is there UB in foo2() as
>>> well?
>>
>> Yes, in the same sense as in `foo1`.
>>
>>> gcc code generator does not think so.
>>
>> It definitely does.

Right.

> Do you have citation from the Standard?

The short answer is section 6.5.6 paragraph 8.

There is amplification in Annex J.2, roughly three pages
after the start of J.2.  You can search for "an array
subscript is out of range", where there is a clarifying
example.

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On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-01 22:54 +0100
  Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-02 00:26 +0200
    Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-01 23:57 +0100
    Re: On Undefined Behavior Kaz Kylheku <046-301-5902@kylheku.com> - 2026-01-02 22:56 +0000
      Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-03 20:48 +0200
      Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-04 14:38 +0100
        Re: On Undefined Behaviour Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-04 21:42 +0000
          Re: On Undefined Behaviour candycanearter07 <candycanearter07@candycanearter07.nomail.afraid> - 2026-01-07 06:40 +0000
        Re: On Undefined Behavior James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-04 16:58 -0500
          Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-05 08:49 +0100
  Re: On Undefined Behavior James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-01 17:49 -0500
  Re: On Undefined Behavior antispam@fricas.org (Waldek Hebisch) - 2026-01-02 05:53 +0000
    Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-02 17:38 +0100
      Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-03 13:30 +0100
  Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-02 10:31 +0100
    Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-02 17:51 +0100
      Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-03 13:42 +0100
        Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-03 14:42 +0100
          Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-03 17:51 +0100
            Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-04 00:20 +0100
  Re: On Undefined Behavior Kaz Kylheku <046-301-5902@kylheku.com> - 2026-01-02 22:52 +0000
    Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-03 23:47 +0100
      Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-04 12:58 +0100
  Re: On Undefined Behavior Andrey Tarasevich <noone@noone.net> - 2026-01-03 07:53 -0800
    Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-04 00:15 +0100
      NULL dereference in embedded [was: On Undefined Behavior] highcrew <high.crew3868@fastmail.com> - 2026-01-04 00:25 +0100
        Re: NULL dereference in embedded [was: On Undefined Behavior] James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-03 18:59 -0500
          Re: NULL dereference in embedded [was: On Undefined Behavior] scott@slp53.sl.home (Scott Lurndal) - 2026-01-04 15:51 +0000
            Re: NULL dereference in embedded [was: On Undefined Behavior] David Brown <david.brown@hesbynett.no> - 2026-01-05 08:55 +0100
        Re: NULL dereference in embedded [was: On Undefined Behavior] Andrey Tarasevich <noone@noone.net> - 2026-01-03 17:24 -0800
          Re: NULL dereference in embedded [was: On Undefined Behavior] Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-04 02:19 +0000
            Re: NULL dereference in embedded [was: On Undefined Behavior] James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-03 21:31 -0500
              Re: NULL dereference in embedded [was: On Undefined Behavior] Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-04 04:52 +0000
                Re: NULL dereference in embedded [was: On Undefined Behavior] James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-04 13:00 -0500
                Re: NULL dereference in embedded [was: On Undefined Behavior] Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-04 21:22 +0000
                Re: NULL dereference in embedded [was: On Undefined Behavior] James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-04 16:53 -0500
                Re: NULL dereference in embedded [was: On Undefined Behavior] Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-05 00:16 +0000
                Re: NULL dereference in embedded [was: On Undefined Behavior] James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-05 06:41 -0500
                Re: NULL dereference in embedded [was: On Undefined Behavior] David Brown <david.brown@hesbynett.no> - 2026-01-05 09:07 +0100
            Re: NULL dereference in embedded [was: On Undefined Behavior] scott@slp53.sl.home (Scott Lurndal) - 2026-01-04 15:56 +0000
          Re: NULL dereference in embedded [was: On Undefined Behavior] Andrey Tarasevich <noone@noone.net> - 2026-01-03 18:44 -0800
        Re: NULL dereference in embedded [was: On Undefined Behavior] David Brown <david.brown@hesbynett.no> - 2026-01-04 17:16 +0100
          Re: NULL dereference in embedded [was: On Undefined Behavior] antispam@fricas.org (Waldek Hebisch) - 2026-01-06 13:08 +0000
            Re: NULL dereference in embedded [was: On Undefined Behavior] Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-06 21:59 +0000
            Re: NULL dereference in embedded [was: On Undefined Behavior] Andrey Tarasevich <noone@noone.net> - 2026-01-07 20:48 -0800
              Re: NULL dereference in embedded [was: On Undefined Behavior] Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-08 23:56 +0000
  Re: On Undefined Behavior Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-01-03 23:14 +0000
  Re: On Undefined Behavior "Paul J. Lucas" <paul@lucasmail.org> - 2026-01-03 17:10 -0800
    Re: On Undefined Behavior highcrew <high.crew3868@fastmail.com> - 2026-01-04 12:51 +0100
      Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-05 15:39 +0100
        Re: On Undefined Behavior "Paul J. Lucas" <paul@lucasmail.org> - 2026-01-06 18:08 -0800
          Re: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-07 11:25 +0100
          Re: On Undefined Behavior James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-07 06:31 -0500
          Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-07 14:10 +0200
  Re: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-09 01:42 -0800
    Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-09 14:36 +0200
      Re: On Undefined Behavior Kaz Kylheku <046-301-5902@kylheku.com> - 2026-01-09 20:14 +0000
        Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-10 18:19 +0200
        Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-10 18:41 +0200
          Re: On Undefined Behavior Kaz Kylheku <046-301-5902@kylheku.com> - 2026-01-13 23:31 +0000
            Re: On Undefined Behavior antispam@fricas.org (Waldek Hebisch) - 2026-01-14 03:57 +0000
            Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-14 10:47 +0200
            Re: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-14 14:49 +0000
        Re: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-10 17:08 +0000
      Re: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-11 11:48 -0800
        Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-11 22:52 +0200
          Re: On Undefined Behavior Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-11 22:53 -0800
            Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-12 11:44 +0200
              Re: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-12 20:29 -0500
          Re: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-03 05:29 -0800
  Re: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-09 15:54 +0200
    Re: On Undefined Behavior wij <wyniijj5@gmail.com> - 2026-01-10 00:08 +0800
  UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-12 16:28 +0200
    Re: UB or not UB? was: On Undefined Behavior bart <bc@freeuk.com> - 2026-01-12 15:58 +0000
      Re: UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-12 20:08 +0200
        Re: UB or not UB? was: On Undefined Behavior scott@slp53.sl.home (Scott Lurndal) - 2026-01-12 20:02 +0000
          Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-12 21:09 -0500
            Re: UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-13 11:31 +0200
              Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-13 22:21 -0500
        Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-13 22:19 -0500
          Re: UB or not UB? was: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-14 09:35 +0100
            Re: UB or not UB? was: On Undefined Behavior antispam@fricas.org (Waldek Hebisch) - 2026-01-14 17:23 +0000
              Re: UB or not UB? was: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-14 12:53 -0800
            Re: UB or not UB? was: On Undefined Behavior Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-14 14:43 -0800
              Re: UB or not UB? was: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-15 11:45 +0100
                Re: UB or not UB? was: On Undefined Behavior James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-01-15 06:16 -0500
                Re: UB or not UB? was: On Undefined Behavior Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-15 04:04 -0800
                Re: UB or not UB? was: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-15 13:56 +0100
                Re: UB or not UB? was: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-03 05:34 -0800
                Re: UB or not UB? was: On Undefined Behavior scott@slp53.sl.home (Scott Lurndal) - 2026-01-15 15:10 +0000
                Re: UB or not UB? was: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-15 16:23 +0100
      Re: UB or not UB? was: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-13 21:54 +0000
        Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-13 21:58 -0500
          Re: UB or not UB? was: On Undefined Behavior Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-13 22:02 -0800
            Re: UB or not UB? was: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-14 14:24 +0000
              Re: UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-14 16:48 +0200
    Re: UB or not UB? was: On Undefined Behavior Andrey Tarasevich <noone@noone.net> - 2026-01-12 08:03 -0800
      Re: UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-12 19:36 +0200
        Re: UB or not UB? was: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-12 12:03 -0800
          Re: UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-12 22:41 +0200
            Re: UB or not UB? was: On Undefined Behavior David Brown <david.brown@hesbynett.no> - 2026-01-13 09:12 +0100
            Re: UB or not UB? was: On Undefined Behavior pa@see.signature.invalid (Pierre Asselin) - 2026-01-13 20:19 +0000
            Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-13 22:20 -0500
            Re: UB or not UB? was: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-03 21:53 -0800
          Re: UB or not UB? was: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-13 23:53 +0000
            Re: UB or not UB? was: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-14 08:06 +0000
        Re: UB or not UB? was: On Undefined Behavior Andrey Tarasevich <noone@noone.net> - 2026-01-13 08:11 -0800
          Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-13 22:10 -0500
          Re: UB or not UB? was: On Undefined Behavior Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-01 22:53 -0800
        Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-13 22:20 -0500
    Re: UB or not UB? was: On Undefined Behavior "James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> - 2026-01-12 20:35 -0500
      Re: UB or not UB? was: On Undefined Behavior Michael S <already5chosen@yahoo.com> - 2026-01-13 11:07 +0200
  Re: On Undefined Behavior Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-01-13 20:37 +0000

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