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Re: int a = a

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: int a = a
Date	2025-03-22 15:37 -0700
Organization	None to speak of
Message-ID	<87ldsw8zer.fsf@nosuchdomain.example.com> (permalink)
References	(10 earlier) <vrhbsf$3e7sn$4@dont-email.me> <87msdfscxj.fsf@nosuchdomain.example.com> <vrjcd5$18m5n$1@dont-email.me> <87pliaqjb9.fsf@nosuchdomain.example.com> <86a59clr3a.fsf@linuxsc.com>

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Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>> David Brown <david.brown@hesbynett.no> writes:
>>> [...]I believe it would be much simpler and clearer if attempting
>>> to read an uninitialised and unassigned local variable were
>>> undefined behaviour in every case.
>>
>> I probably agree (I haven't given it all that much thought), but
>> the committee made a specific decision between C90 and C99 to say
>> that reading an uninitialized automatic object is *not* undefined
>> behavior.  I'm don't know why they did that (though, all else
>> being equal, reducing the number of instances of undefined
>> behavior is a good thing), but reversing that decision for this
>> one issue is not something they decided to do.
>
> Your description of what was done is wrong.  It is still the case in
> C99 that trying to access an uninitialized object is undefined
> behavior, at least potentially, except for accesses using a type
> that either is a character type or has no trap representations (and
> all types other than unsigned char may have trap representations,
> depending on the implementation).  A statement like
>
>     int a = a;
>
> may still be given a warning as potential undefined behavior, even
> in C99.

I had already mentioned that distinction earlier in the thread.

[...]

> The mistake is thinking that UB for uninitialized access was
> removed in C99.  It wasn't.  Narrowed, yes;  removed, no.

Acknowledged.

[...]

-- 
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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Bart's Language bart <bc@freeuk.com> - 2025-03-17 23:51 +0000
  Re: Bart's Language antispam@fricas.org (Waldek Hebisch) - 2025-03-18 12:17 +0000
    Re: Bart's Language bart <bc@freeuk.com> - 2025-03-18 13:54 +0000
      Re: Bart's Language antispam@fricas.org (Waldek Hebisch) - 2025-03-18 15:10 +0000
        Re: Bart's Language bart <bc@freeuk.com> - 2025-03-18 15:45 +0000
          Re: Bart's Language David Brown <david.brown@hesbynett.no> - 2025-03-18 17:31 +0100
            int a = a (Was: Bart's Language) gazelle@shell.xmission.com (Kenny McCormack) - 2025-03-18 18:04 +0000
              Re: int a = a (Was: Bart's Language) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-03-18 19:36 +0100
                Re: int a = a (Was: Bart's Language) Kaz Kylheku <643-408-1753@kylheku.com> - 2025-03-18 19:11 +0000
                Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-19 15:56 +0100
                Re: int a = a (Was: Bart's Language) scott@slp53.sl.home (Scott Lurndal) - 2025-03-19 16:38 +0000
                Re: int a = a (Was: Bart's Language) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-03-19 14:29 -0700
                Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-20 09:39 +0100
                Re: int a = a (Was: Bart's Language) bart <bc@freeuk.com> - 2025-03-20 11:59 +0000
                Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-20 15:46 +0100
                Re: int a = a (Was: Bart's Language) wij <wyniijj5@gmail.com> - 2025-03-20 23:13 +0800
                Re: int a = a (Was: Bart's Language) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-20 02:02 -0700
                Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-20 15:57 +0100
                Re: int a = a (Was: Bart's Language) Kaz Kylheku <643-408-1753@kylheku.com> - 2025-03-19 17:07 +0000
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-19 13:34 -0700
                Re: int a = a Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-20 02:54 -0700
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-20 03:20 -0700
                Re: int a = a David Brown <david.brown@hesbynett.no> - 2025-03-20 16:22 +0100
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-20 12:46 -0700
                Re: int a = a David Brown <david.brown@hesbynett.no> - 2025-03-21 10:44 +0100
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-21 12:23 -0700
                Re: int a = a David Brown <david.brown@hesbynett.no> - 2025-03-21 21:46 +0100
                Re: int a = a Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-22 13:59 -0700
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-22 15:37 -0700
                Re: int a = a David Brown <david.brown@hesbynett.no> - 2025-03-20 15:42 +0100
              Re: int a = a (Was: Bart's Language) scott@slp53.sl.home (Scott Lurndal) - 2025-03-18 19:37 +0000
              Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-18 20:51 +0100
                Re: int a = a (Was: Bart's Language) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-03-18 23:27 +0100
                Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-19 11:40 +0100
              Re: int a = a (Was: Bart's Language) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-18 23:52 -0700
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-19 01:55 -0700
                Re: int a = a (Was: Bart's Language) David Brown <david.brown@hesbynett.no> - 2025-03-19 11:43 +0100
                Re: int a = a (Was: Bart's Language) Rosario19 <Ros@invalid.invalid> - 2025-03-19 13:23 +0100
                Re: int a = a (Was: Bart's Language) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-20 01:32 -0700
          Re: Bart's Language antispam@fricas.org (Waldek Hebisch) - 2025-03-20 22:55 +0000
            Re: Bart's Language Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-03-20 16:22 -0700
              Re: Bart's Language antispam@fricas.org (Waldek Hebisch) - 2025-03-22 14:37 +0000
                Re: Bart's Language James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-03-22 11:41 -0400
                Re: Bart's Language antispam@fricas.org (Waldek Hebisch) - 2025-03-22 16:52 +0000
                Re: Bart's Language James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-03-22 20:12 -0400
                By definition... (Was: Bart's Language) gazelle@shell.xmission.com (Kenny McCormack) - 2025-03-23 17:20 +0000
        Re: Bart's Language bart <bc@freeuk.com> - 2025-03-18 22:19 +0000
          Re: Bart's Language antispam@fricas.org (Waldek Hebisch) - 2025-03-20 22:38 +0000
            Re: Bart's Language Kaz Kylheku <643-408-1753@kylheku.com> - 2025-03-20 23:45 +0000
              Re: Bart's Language bart <bc@freeuk.com> - 2025-03-21 00:56 +0000
                Re: Bart's Language Kaz Kylheku <643-408-1753@kylheku.com> - 2025-03-21 17:47 +0000
                Re: Bart's Language Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-22 07:12 -0700
            Re: Bart's Language bart <bc@freeuk.com> - 2025-03-21 00:33 +0000

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