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Groups > comp.lang.c > #162782

Re: C23 (C2x) changes

From Bart <bc@freeuk.com>
Newsgroups comp.lang.c
Subject Re: C23 (C2x) changes
Date 2021-09-20 23:05 +0100
Organization A noiseless patient Spider
Message-ID <sib0ie$uve$1@dont-email.me> (permalink)
References <si99fr$ma4$1@dont-email.me> <siaa3b$t76$1@dont-email.me> <siac7m$8r0$1@dont-email.me> <siahul$tb8$1@dont-email.me> <siao15$qbr$1@dont-email.me>

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On 20/09/2021 20:39, David Brown wrote:
> On 20/09/2021 19:55, Bart wrote:
>> On 20/09/2021 17:17, David Brown wrote:

>>> For those that think it makes sense to have a pile of 2147483647 apples,
>>> add another apple to the pile, and end up with -2147483648 apples, gcc
>>> still has the "-fwrapv" option.
>>
>> Of course it makes perfect sense to have a pile of 4294967295 apples,
>> add another apple to the pile, and suddenly end up with 0 apples!
> 
> I don't think it does make sense - although it is a good deal less silly
> than wrapping signed integers.  Unsigned types in C model modulo
> arithmetic precisely - signed types model integer arithmetic with size
> limitations.  In integer arithmetic, and in C signed arithmetic, you
> can't add two positive numbers and get a negative number.  That seems
> pretty obvious and sensible to me.
> 
>>
>> Meanwhile, someone could remove that extra apple from the pile of
>> -2147483648, to restore the original 2147483647, however that's too
>> late: the overflow police have already been, and will do so again even
>> when it becomes legal.
>>
> 
> "Someone could remove an apple from a pile of -2147483648 apples" ?  Do
> you not see how nonsensical that is?

Try this program, where the number of applies is represented with an 
8-bit value:

     int8_t apples;

     apples = 127;
     printf("Initial pile of apples: %d\n",apples);
     apples += 1;
     printf("After adding one more apple: %d\n",apples);
     apples -= 1;
     printf("After removing an apple: %d\n",apples);

The number of apples goes from 127 to -128, and back to 127, just like 
my example using 32 bits.

Yet, this is not NOT undefined behaviour, and is suddenly sensible in 
the eyes of C?

Same with 16 bits. And same with 32 bits IF C had adopted a 64-bit int.

All I see is inconsistency if you say one is UB but not another.

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Thread

C23 (C2x) changes Mehdi Amini <atorrses@gmail.com> - 2021-09-20 10:54 +0430
  Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 09:35 +0200
    Re: C23 (C2x) changes Mehdi Amini <atorrses@gmail.com> - 2021-09-21 11:01 +0430
  Re: C23 (C2x) changes John Bode <jfbode1029@gmail.com> - 2021-09-20 10:41 -0500
    Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 18:17 +0200
      Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 18:55 +0100
        Re: C23 (C2x) changes scott@slp53.sl.home (Scott Lurndal) - 2021-09-20 18:21 +0000
        Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 21:39 +0200
          Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 21:07 +0100
            Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-20 22:59 +0200
              Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 22:29 +0100
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-20 17:43 -0700
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-21 17:56 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-21 18:05 +0100
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-21 11:42 -0700
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-22 11:37 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-22 11:55 +0100
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-22 14:21 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-22 13:58 +0100
                Re: C23 (C2x) changes Ian Pilcher <arequipeno@gmail.com> - 2021-09-22 12:02 -0500
                Re: C23 (C2x) changes scott@slp53.sl.home (Scott Lurndal) - 2021-09-22 17:19 +0000
          Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-20 23:05 +0100
            Re: C23 (C2x) changes scott@slp53.sl.home (Scott Lurndal) - 2021-09-20 22:47 +0000
              Re: C23 (C2x) changes Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-09-20 22:58 +0000
              Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-02 07:16 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 15:15 +0000
            Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-20 17:45 -0700
        Re: C23 (C2x) changes Manfred <noname@add.invalid> - 2021-09-27 17:15 +0200
          Re: C23 (C2x) changes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-27 17:38 +0100
            Re: C23 (C2x) changes Manfred <noname@add.invalid> - 2021-09-27 23:18 +0200
              Re: C23 (C2x) changes antispam@math.uni.wroc.pl - 2021-09-28 13:53 +0000
              Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-02 08:07 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 15:18 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-02 15:04 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 01:58 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-02 22:06 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 10:43 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-03 13:30 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 05:04 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-03 23:24 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 06:54 +0000
                Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-04 09:58 +0200
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 15:52 +0000
                Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-04 10:45 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 20:30 +0000
                Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 03:57 -0700
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-06 12:27 +0000
          Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-29 03:38 +0000
      Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-15 11:35 +0100
        Re: C23 (C2x) changes Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-10-15 18:27 +0000
          Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-15 20:08 +0100
          Re: C23 (C2x) changes Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-10-15 19:20 +0000
            Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-15 21:50 +0100
    Re: C23 (C2x) changes Florian Weimer <fw@deneb.enyo.de> - 2021-10-03 09:43 +0200
      Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-03 18:53 +0200
      Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-03 13:55 -0700
  Re: C23 (C2x) changes William Ahern <william@25thandClement.com> - 2021-09-21 22:57 -0700
    Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-02 08:55 -0700
      Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 16:36 +0000
  Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-09-22 20:27 +0200
    Re: C23 (C2x) changes Philipp Klaus Krause <pkk@spth.de> - 2021-09-22 22:25 +0200
      Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-22 14:05 -0700
        Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-09-22 23:24 +0100
          Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-22 18:49 -0700
        Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-09-23 18:47 +0200
  Static bounds checking (was Re: C23 (C2x) changes) William Ahern <william@25thandClement.com> - 2021-09-23 21:11 -0700
    Re: Static bounds checking (was Re: C23 (C2x) changes) David Brown <david.brown@hesbynett.no> - 2021-09-24 08:51 +0200
      Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-24 09:30 +0200
    Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-24 07:52 +0000
      Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-24 12:32 +0200
        Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-24 10:49 +0000
          Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-24 14:46 +0200
      Re: Static bounds checking (was Re: C23 (C2x) changes) Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-24 18:14 +0200
        Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 01:00 +0000
          Re: Static bounds checking (was Re: C23 (C2x) changes) Philipp Klaus Krause <pkk@spth.de> - 2021-09-25 07:44 +0200
            Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 11:28 +0000
            Re: Static bounds checking (was Re: C23 (C2x) changes) antispam@math.uni.wroc.pl - 2021-09-28 10:56 +0000
          Re: Static bounds checking (was Re: C23 (C2x) changes) Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 09:48 +0200
            Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 11:30 +0000
              Re: Static bounds checking (was Re: C23 (C2x) changes) Kaz Kylheku <480-992-1380@kylheku.com> - 2021-09-25 20:49 +0000
                Re: Static bounds checking (was Re: C23 (C2x) changes) Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-26 00:04 +0000
              Re: Static bounds checking (was Re: C23 (C2x) changes) Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-26 06:56 +0200
  Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-27 10:15 -0700
    Re: C23 (C2x) changes Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-27 11:15 -0700
      Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-09-27 22:11 +0200
      Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-27 14:20 -0700
        Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-09-27 14:31 -0700
      Re: C23 (C2x) changes Mehdi Amini <atorrses@gmail.com> - 2021-09-28 10:43 +0330
  Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 04:01 -0700
    Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-10-06 04:42 -0700
      Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-29 04:04 -0700
        Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-29 16:34 +0200
    Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-06 19:07 +0200
      Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-07 11:06 +0200
        Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-07 19:31 +0200
          Re: C23 (C2x) changes David Brown <david.brown@hesbynett.no> - 2021-10-07 22:14 +0200
            Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-10-08 06:18 -0700
              Re: C23 (C2x) changes Thiago Adams <thiago.adams@gmail.com> - 2021-10-08 06:21 -0700
      Re: C23 (C2x) changes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-29 04:01 -0700
    Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-15 12:59 +0200
      Re: C23 (C2x) changes Jim Jackson <jj@franjam.org.uk> - 2021-10-15 16:50 +0000
        Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-16 07:51 +0200
          Re: C23 (C2x) changes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-16 11:50 -0700
            Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-16 21:28 +0200
              Re: C23 (C2x) changes Jim Jackson <jj@franjam.org.uk> - 2021-10-17 17:18 +0000
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-17 20:00 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-17 19:17 +0100
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-18 06:49 +0200
                Re: C23 (C2x) changes Bart <bc@freeuk.com> - 2021-10-18 11:23 +0100
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-18 14:09 +0200
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-21 01:07 +0000
                Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-21 01:02 +0000
          Re: C23 (C2x) changes Guillaume <message@bottle.org> - 2021-10-16 21:28 +0200
            Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-17 06:04 +0200
              Re: C23 (C2x) changes Manfred <noname@add.invalid> - 2021-10-17 19:35 +0200
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-17 20:01 +0200
                Re: C23 (C2x) changes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-17 14:15 -0700
              Re: C23 (C2x) changes Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-21 01:02 +0000
                Re: C23 (C2x) changes Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-21 13:15 +0200

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