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Groups > comp.lang.c > #393215
| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Regarding assignment to struct |
| Date | 2025-05-06 13:06 -0700 |
| Organization | None to speak of |
| Message-ID | <87msbpfqs5.fsf@nosuchdomain.example.com> (permalink) |
| References | (5 earlier) <vv9stv$2i8j$1@dont-email.me> <20250505120145.000014f8@yahoo.com> <vvame5$ppqp$1@dont-email.me> <87jz6uhkgo.fsf@nosuchdomain.example.com> <vvdhb2$3m8gn$1@paganini.bofh.team> |
antispam@fricas.org (Waldek Hebisch) writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>> Andrey Tarasevich <noone@noone.net> writes:
>> [...]
>>> #include <stdio.h>
>>>
>>> struct S { int a[10]; };
>>>
>>> int main()
>>> {
>>> struct S a, b = { 0 };
>>> int *pa, *pb, *pc;
>>>
>>> pa = &a.a[5],
>>> pb = &b.a[5],
>>> pc = &(a = b).a[5],
>>> printf("%p %p %p\n", (void *) pa, (void *) pb, (void *) pc);
>>> }
>>>
>>> This version has no UB.
>>
>> I believe it does. pc points to an element of an object with
>> temporary lifetime. The value of pc is then used after the object
>> it points to has reached the end of its lifetime. At that point,
>> pc has an indeterminate value.
>>
>> N3096 6.2.4p2: "If a pointer value is used in an evaluation after
>> the object the pointer points to (or just past) reaches the end of
>> its lifetime, the behavior is undefined. The representation of a
>> pointer object becomes indeterminate when the object the pointer
>> points to (or just past) reaches the end of its lifetime."
>
> Note commas above. Assignment to pc and call to printf are parts
> of a single expression, so use of pc is within lifetime of the
> temporary object.
Right, I didn't see the commas and assumed semicolons. Changing the
formatting would have made the point much clearer.
--
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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Regarding assignment to struct Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2025-05-02 18:34 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-02 13:17 -0700
Re: Regarding assignment to struct Barry Schwarz <schwarzb@delq.com> - 2025-05-02 13:35 -0700
That depends... (Was: Regarding assignment to struct) gazelle@shell.xmission.com (Kenny McCormack) - 2025-05-02 20:44 +0000
Re: That depends... (Was: Regarding assignment to struct) Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2025-05-03 01:13 +0000
Re: That depends... (Was: Regarding assignment to struct) Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-05-03 02:28 +0000
Re: That depends... (Was: Regarding assignment to struct) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-05-03 06:17 +0200
Re: That depends... (Was: Regarding assignment to struct) Kaz Kylheku <643-408-1753@kylheku.com> - 2025-05-03 04:31 +0000
Re: That depends... (Was: Regarding assignment to struct) Kaz Kylheku <643-408-1753@kylheku.com> - 2025-05-03 05:11 +0000
Re: That depends... (Was: Regarding assignment to struct) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-05-05 12:30 +0200
Re: That depends... (Was: Regarding assignment to struct) Kaz Kylheku <643-408-1753@kylheku.com> - 2025-05-05 18:47 +0000
Re: That depends... (Was: Regarding assignment to struct) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-04 11:05 -0700
Re: That depends... (Was: Regarding assignment to struct) James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-05-03 00:47 -0400
Re: That depends... (Was: Regarding assignment to struct) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-04 10:59 -0700
Re: That depends... (Was: Regarding assignment to struct) Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2025-05-04 18:16 +0000
Re: Regarding assignment to struct antispam@fricas.org (Waldek Hebisch) - 2025-05-02 21:35 +0000
Re: Regarding assignment to struct Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2025-05-03 01:43 +0000
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-03 01:14 -0700
Re: Regarding assignment to struct Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-05-03 22:46 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-03 17:37 -0700
Re: Regarding assignment to struct James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-05-03 23:38 -0400
Re: Regarding assignment to struct gazelle@shell.xmission.com (Kenny McCormack) - 2025-05-04 09:25 +0000
Re: Regarding assignment to struct scott@slp53.sl.home (Scott Lurndal) - 2025-05-04 14:27 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-04 18:45 +0200
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-04 13:20 -0700
Re: Regarding assignment to struct scott@slp53.sl.home (Scott Lurndal) - 2025-05-05 00:41 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-04 18:42 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 21:57 -0700
Re: Regarding assignment to struct James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-05-04 21:08 -0400
Re: Regarding assignment to struct Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-05-03 22:47 +0000
Re: Regarding assignment to struct Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-05-03 22:46 +0000
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-04 06:48 -0700
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-04 22:22 -0700
Re: Regarding assignment to struct Michael S <already5chosen@yahoo.com> - 2025-05-05 11:12 +0300
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-05 01:29 -0700
Re: Regarding assignment to struct Michael S <already5chosen@yahoo.com> - 2025-05-05 12:01 +0300
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 07:14 -0700
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-05 08:45 -0700
Re: Regarding assignment to struct Michael S <already5chosen@yahoo.com> - 2025-05-05 20:20 +0300
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 22:26 -0700
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-29 05:11 -0700
Re: Regarding assignment to struct James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-05-29 12:57 -0400
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 13:27 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 17:04 -0700
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 17:53 -0700
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-06 11:35 +0200
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-29 05:19 -0700
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-29 21:05 +0200
Re: Regarding assignment to struct antispam@fricas.org (Waldek Hebisch) - 2025-05-06 17:36 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-06 20:46 +0200
Re: Regarding assignment to struct scott@slp53.sl.home (Scott Lurndal) - 2025-05-06 19:22 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-07 09:37 +0200
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-29 05:49 -0700
Re: Regarding assignment to struct Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-05-29 16:33 +0200
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-29 21:20 +0200
Re: Regarding assignment to struct scott@slp53.sl.home (Scott Lurndal) - 2025-05-29 21:15 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-29 14:54 -0700
Re: Regarding assignment to struct scott@slp53.sl.home (Scott Lurndal) - 2025-05-30 14:29 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-30 10:50 +0200
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-06 13:06 -0700
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-29 05:21 -0700
Re: Regarding assignment to struct Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-05-29 16:43 +0200
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-29 05:14 -0700
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-29 13:56 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 07:03 -0700
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 01:26 -0700
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-05 10:14 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-08 12:45 -0700
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-08 22:20 +0200
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 01:34 -0700
Re: Regarding assignment to struct Michael S <already5chosen@yahoo.com> - 2025-05-05 12:03 +0300
Re: Regarding assignment to struct gazelle@shell.xmission.com (Kenny McCormack) - 2025-05-05 11:30 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 13:32 -0700
Re: Regarding assignment to struct Kaz Kylheku <643-408-1753@kylheku.com> - 2025-05-05 21:10 +0000
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 22:57 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 22:40 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 06:34 -0700
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 13:43 -0700
Re: Regarding assignment to struct Nick Bowler <nbowler@draconx.ca> - 2025-05-06 19:06 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-06 13:21 -0700
Re: Regarding assignment to struct Nick Bowler <nbowler@draconx.ca> - 2025-05-07 19:09 +0000
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-07 14:23 -0700
Re: Regarding assignment to struct Nick Bowler <nbowler@draconx.ca> - 2025-05-08 12:58 +0000
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-07 21:17 -0700
Re: Regarding assignment to struct Andrey Tarasevich <noone@noone.net> - 2025-05-29 05:36 -0700
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-29 14:36 -0700
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 07:56 -0700
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-05 20:00 +0200
Re: Regarding assignment to struct NotAorB <atod101101@gmail.com> - 2025-05-12 16:38 -0400
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-03 11:46 +0200
Re: Regarding assignment to struct Muttley@dastardlyhq.com - 2025-05-05 08:50 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-05 13:34 +0200
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-05 13:53 -0700
Re: Regarding assignment to struct Muttley@DastardlyHQ.org - 2025-05-06 07:16 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-06 11:46 +0200
Re: Regarding assignment to struct Muttley@DastardlyHQ.org - 2025-05-06 10:18 +0000
Re: Regarding assignment to struct Michael S <already5chosen@yahoo.com> - 2025-05-06 16:34 +0300
Re: Regarding assignment to struct Richard Damon <richard@damon-family.org> - 2025-05-03 21:42 -0400
Re: Regarding assignment to struct Michael S <already5chosen@yahoo.com> - 2025-05-04 11:01 +0300
Re: Regarding assignment to struct Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-05-04 08:34 +0000
Re: Regarding assignment to struct David Brown <david.brown@hesbynett.no> - 2025-05-04 14:06 +0200
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-05 21:25 -0700
Re: Regarding assignment to struct Rosario19 <Ros@invalid.invalid> - 2025-05-12 11:23 +0200
Re: Regarding assignment to struct Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-05-04 07:49 -0700
Re: Regarding assignment to struct Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-05-04 14:09 -0700
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