Re: how cast works?

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: how cast works?
Date	2024-08-08 16:14 -0700
Organization	None to speak of
Message-ID	<87frre8v5q.fsf@nosuchdomain.example.com> (permalink)
References	(4 earlier) <20240808193203.00006287@yahoo.com> <v92va5$4msg$1@dont-email.me> <v9310a$4v1a$2@dont-email.me> <v93565$6ffo$1@dont-email.me> <v93h12$9vom$1@dont-email.me>

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David Brown <david.brown@hesbynett.no> writes:
[...]
> A _Bool is always either 0 or 1.  The conversion is whatever the
> compiler needs to give an int of value 0 or 1.

The value of a _Bool object is always either 0 or 1 *unless* the program
does something weird.

C23 is a bit clearer about the representation of bool (still also called
_Bool) than previous editions.  It states (draft N3220) that :

    The type bool shall have one value bit and (sizeof(bool)*CHAR_BIT)-1
    padding bits.

There are several ways to force a representation other than 00000000 or
00000001 into a _Bool object, including a union, memset(), or type
punning via a pointer cast.

C23 dropped the term "trap representation", replacing it with "non-value
representation" -- a reasonable change, since accessing a trap
representation is not guaranteed to cause the program to "perform a
trap" (defined as "interrupt execution of the program such that no
further operations are performed").

It doesn't specify whether setting the padding bits to 1 results in a
non-value representation.

If non-zero padding bits create a non-value representation, then
accessing a bool object holding such a representation has undefined
behavior.  It could, among other things, yield the same value implied by
the representation as if it were an ordinary integer of the same size.

If there are no non-value representations, then only the
single value bit determines the value, which is either false or true.

As you mentioned, I expect that sizeof (bool) will normally be 1, but an
implementation could make it wider, e.g. with 1 value bit and 31 padding
bits.

[...]

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */

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how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-07 08:28 -0300
  Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-07 08:33 -0300
    Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-07 13:13 -0700
    Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 17:43 -0700
      Re: how cast works? Vir Campestris <vir.campestris@invalid.invalid> - 2024-08-12 11:51 +0100
        Challenge/exercise problem - signum() function Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-12 08:17 -0700
          Re: Challenge/exercise problem - signum() function Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2024-08-12 16:07 +0000
            Re: Challenge/exercise problem - signum() function Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-12 09:57 -0700
  Re: how cast works? Dan Purgert <dan@djph.net> - 2024-08-07 20:00 +0000
    Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-07 13:26 -0700
    Re: how cast works? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-08-07 23:00 +0000
    Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 08:14 -0300
      Re: how cast works? Bart <bc@freeuk.com> - 2024-08-08 14:23 +0100
        Re: how cast works? Michael S <already5chosen@yahoo.com> - 2024-08-08 19:32 +0300
          Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 14:11 -0300
          Re: how cast works? Bart <bc@freeuk.com> - 2024-08-08 18:29 +0100
            Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 14:50 -0300
              Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 14:57 -0300
              Re: how cast works? Bart <bc@freeuk.com> - 2024-08-08 19:01 +0100
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 15:13 -0300
              Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-08 12:29 -0700
            Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-08 19:58 +0200
              Re: how cast works? Bart <bc@freeuk.com> - 2024-08-08 20:09 +0100
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 00:32 +0200
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-08 16:14 -0700
                Re: how cast works? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-08-09 02:47 +0000
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-08 22:55 -0700
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-09 02:08 -0400
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 18:16 +0200
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 12:18 -0700
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 17:07 -0700
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-11 20:14 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-09 01:56 +0100
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 19:08 +0200
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-10 11:03 +0100
                Re: how cast works? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-08-09 02:45 +0000
      Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-08 12:42 -0700
        Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 17:34 -0300
          Re: how cast works? Bart <bc@freeuk.com> - 2024-08-08 22:41 +0100
            Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-08 16:17 -0700
              Re: how cast works? Bart <bc@freeuk.com> - 2024-08-09 11:04 +0100
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 19:12 +0200
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-12 15:36 +0100
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-09 13:57 -0400
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-09 21:59 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 14:47 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-10 00:32 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 17:12 -0700
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-09 18:29 -0400
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-13 11:18 +0200
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-13 11:34 +0100
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-13 07:51 -0400
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-13 14:01 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-13 12:46 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-13 21:51 +0100
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-13 16:46 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-14 00:56 +0100
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-18 03:37 -0700
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 14:29 -0700
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-09 18:35 -0400
                Re: how cast works? Kaz Kylheku <643-408-1753@kylheku.com> - 2024-08-09 21:30 +0000
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 14:57 -0700
                Re: how cast works? Kaz Kylheku <643-408-1753@kylheku.com> - 2024-08-09 23:14 +0000
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 16:58 -0700
                Re: how cast works? Kaz Kylheku <643-408-1753@kylheku.com> - 2024-08-10 00:06 +0000
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 17:27 -0700
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-09 20:31 -0400
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-10 01:11 +0100
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-13 11:23 +0200
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 17:32 -0700
                Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-09 18:35 -0400
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 17:27 -0700
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 12:23 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-09 21:31 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 13:49 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-09 22:01 +0100
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-12 00:33 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-12 12:21 +0100
              Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 17:46 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-12 02:00 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-11 20:23 -0700
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 20:37 -0700
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-11 21:33 -0700
                Re: how cast works? Ben Bacarisse <ben@bsb.me.uk> - 2024-08-12 16:57 +0100
                Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-12 10:04 -0700
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-12 13:35 -0700
            Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-09 07:57 -0300
              Re: how cast works? Bart <bc@freeuk.com> - 2024-08-09 16:25 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 12:06 -0700
              Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 19:20 +0200
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-09 15:54 -0300
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-09 16:05 -0300
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 21:43 +0200
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 13:28 -0700
                Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 22:01 +0200
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-10 11:17 +0100
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-10 10:15 -0300
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-10 17:14 +0100
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-10 20:01 -0300
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-10 17:10 -0700
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-11 09:23 -0300
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-11 13:30 +0100
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-11 14:16 -0300
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-11 13:38 -0700
                Re: how cast works? Bart <bc@freeuk.com> - 2024-08-12 12:24 +0100
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 13:26 -0700
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-09 18:01 -0300
                Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 14:53 -0700
              Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-09 12:03 -0700
                Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-09 16:22 -0300
          Re: how cast works? David Brown <david.brown@hesbynett.no> - 2024-08-09 00:36 +0200
    Re: how cast works? Dan Purgert <dan@djph.net> - 2024-08-08 14:08 +0000
    Re: how cast works? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-08-09 02:42 +0000
  Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-07 13:08 -0700
    Re: how cast works? Thiago Adams <thiago.adams@gmail.com> - 2024-08-08 08:35 -0300
      Re: how cast works? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-08 12:39 -0700
      Re: how cast works? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-08 18:40 -0400
        Re: how cast works? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 17:15 -0700
    Is there an audio book version (Was: how cast works?) gazelle@shell.xmission.com (Kenny McCormack) - 2024-08-08 16:19 +0000
  Re: how cast works? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-08-07 23:03 +0000

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