Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #396234

Re: Bart's Language

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: Bart's Language
Date 2026-01-06 14:04 -0800
Organization A noiseless patient Spider
Message-ID <86seciqtxs.fsf@linuxsc.com> (permalink)
References (4 earlier) <vrc4eb$2p28t$1@dont-email.me> <vri6co$26v8m$2@paganini.bofh.team> <87a59fs2xm.fsf@nosuchdomain.example.com> <86wmb58mi6.fsf@linuxsc.com> <877c35pa37.fsf@nosuchdomain.example.com>

Show all headers | View raw

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>
>>> antispam@fricas.org (Waldek Hebisch) writes:
>>> [...]
>>>
>>>> Well, it is rather easy to see if variable is used within its
>>>> own initialization, so practically it is minor gap.  Of course,
>>>> there is problem with C standard:  IIUC depending on rest of
>>>> the code declarations as above are merely undefined behaviour
>>>> or even produce unspecified value.  So C compiler is
>>>> forbidden to stop compilation are report compile time error.
>>>
>>> Valid responses to undefined behavior include "terminating a translation
>>> or execution (with the issuance of a diagnostic message)".
>>
>> That's true, but doing so is allowed only if the circumstances
>> of undefined behavior have occurred.  In the case of compiling
>> a declaration such as
>>
>>     int a = a;
>>
>> no undefined behavior has as yet occurred.
>
> N3096 6.3.2.1p2 (lvalue conversion):
>
>     If the lvalue designates an object of automatic storage duration
>     that could have been declared with the register storage class (never
>     had its address taken), and that object is uninitialized (not
>     declared with an initializer and no assignment to it has been
>     performed prior to use), the behavior is undefined.
>
> Strictly speaking, `a` doesn't meet the definition of
> "uninitialized", since it is declared with an initializer, but
> its value is accessed before the initialization has been executed.
> I'm not entirely certain that `int a = a;` has undefined behavior,
> but it's unclear that the behavior is defined.

Clearly the term "uninitialized" is meant to refer to a dynamic
property, not a static property.  At the point on the right side
of the '=' where the access is performed, the object designated
by 'a' has not been initialized.

>>> In other
>>> words, if a compiler is able to prove that a program has undefined
>>> behavior (that will occur on each execution), it can reject it at
>>> compile time.
>>
>> The program can be rejected, but not because of the rule about
>> terminating a translation.  The program can be rejected because
>> the program is not strictly conforming, and implementations are
>> not required to accept programs that are not strictly conforming.
>
> I disagree, but we've gone over this before with no resolution.

Have you ever offered reasoning to explain your belief, or
did you give just an unsupported conclusion?  Can you explain
the reasoning that underlies your disagreement?

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

Thread

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 Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-04-28 09:39 -0700
                Re: int a = a Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-04-29 13:12 -0700
                Re: int a = a Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-04-29 13:34 -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 Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-04-27 13:41 -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 Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-04-27 11:53 -0700
                Re: Bart's Language Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-04-27 14:29 -0700
                Re: Bart's Language Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-06 14:04 -0800
                Re: Bart's Language Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-01-06 17:12 -0800
                Re: Bart's Language Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-06 09:04 -0800
        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

csiph-web