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

From	Michael S <already5chosen@yahoo.com>
Newsgroups	comp.lang.c
Subject	Re: UB or not UB? was: On Undefined Behavior
Date	2026-01-13 11:07 +0200
Organization	A noiseless patient Spider
Message-ID	<20260113110727.00005477@yahoo.com> (permalink)
References	<10j6qdt$3q9n4$1@dont-email.me> <20260112162857.00003dd8@yahoo.com> <10k47gd$15aeb$5@dont-email.me>

Show all headers | View raw

On Mon, 12 Jan 2026 20:35:09 -0500
"James Russell Kuyper Jr." <jameskuyper@alumni.caltech.edu> wrote:

> On 12/01/2026 14:28, Michael S wrote:
> > On Thu, 1 Jan 2026 22:54:05 +0100  
> 
> > On related note.
> > 
> > 
> > struct bar1 {
> >    int table[4];
> >    int other_table[4];
> > };
> > 
> > struct bar2 {
> >    int other_table[4];
> >    int table[4];
> > };
> > 
> > int foo1(struct bar1* p, int v)
> > {
> >    for (int i = 0; i <= 4; ++i)
> >      if (p->table[i] == v)
> >        return 1;
> >    return 0;
> > }
> > 
> > 
> > int foo2(struct bar2* p, int v)
> > {
> >    for (int i = 0; i <= 4; ++i)
> >      if (p->table[i] == v)
> >        return 1;
> >    return 0;
> > }
> > 
> > According to C Standard, access to p->table[4] in foo1() is UB.
> > [O.T.]
> > I want to use language (or, better, standardize dialect of C) in
> > which behavior in this case is defined, but I am bad at influencing
> > other people. So can not get what I want.  
> 
> OK - so how do you want it to be defined? I've used languages where 
> table[n] for n>3 would have exactly the same effect as table[3], and 
> table[n] for n<0 would have exactly the same effect as table[0]. I've 
> seen algorithms that were actually simplified by relying upon this
> behavior.

I want "my" dialect to be based on abstract machine with flat memory
model. All variables, except for automatic variables which address
was never taken by the program, are laid upon one big implicit
array of char. 
For my purposes, Harvard abstract machine is sufficient. 
I am sure that there are multiple people that would want option for Von
Neumann abstract machine, i.e. for program code to be laid over the same
implicit array as variables, with as many things defined in the
standard as practically possible. My aspirations do not go that far.

In specific case of 'struct bar1', it means that I want p->table[4:7] to
be absolute equivalents of p->other_table[0:3]. For p->table[n] where n
< 0 or n > 7,  I want generated code to access respective locations in
implicit underlying array. Whether resulting behavior defined or
undefined would depend on the specifics of the caller.

If you say that "my" dialect is less optimizable than Standard C then
my answer is "Yes, I know and I don't care". 

If you say that "my" dialect removes certain potential for detection of
buffer overflows by compiler then my answer is "Generally, yes, and it's
not great, but I consider it a fair price.". Pay attention that there
are still plenty of places where compiler can warn, like in majority of
automatic and static arrays. In other situations bound checking can be
enabled at spot by special attribute.

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

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

csiph-web