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Groups > comp.lang.c > #390278
| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Two questions on arrays with size defined by variables |
| Date | 2025-02-09 22:49 -0800 |
| Organization | None to speak of |
| Message-ID | <87cyfqpa55.fsf@nosuchdomain.example.com> (permalink) |
| References | (3 earlier) <voae3a$2rke4$1@paganini.bofh.team> <voao29$o6uh$2@dont-email.me> <87bjvar83h.fsf@nosuchdomain.example.com> <vobna3$tmev$1@dont-email.me> <voc68c$13fkt$1@dont-email.me> |
Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
> On 10.02.2025 03:12, Janis Papanagnou wrote:
[...]
>> The Cim compiler I use actually supports a constant initialization -
>> but I'm positive this is non-standard! - like
>>
>> begin
>> integer n = 10;
>> integer array arr (1:n);
>> arr(5) := 9;
>> end
>
> I should have noted that this (non-standard) syntax doesn't really
> address the problem (since you have just a named constant that you
> may use in several places, but the array is *not* really dynamic,
> its memory demands are fixed and known for that block).
>
> I think the primary point for an explanation of the necessity of a
> block structure is different. - It is typical that stack memory is
> allocated when a block is "entered". For the stack allocation the
> size of all local objects should be known. But in the first example
> above the outer block has only knowledge about the size of the 'n'
> integer variable, but without a concrete value for 'n' we don't
> know how many space the dynamic array will need. But if we open a
> new (subordinated) block the array size is determined if declared
> there.
In C lifetime of a non-VLA object with automatic storage duration
(defined within a block without "static") extends from when execution
reaches the opening "{" of the enclosing block to when it reaches the
closing "}". There are well-defined ways you can even access such an
object in code that appears textually before its definition (by saving
its address and using a goto). This means that a conforming
implementation *must* allocate memory for non-VLA automatic objects on
block entry; waiting until the definition is encountered would be
non-conforming.
But a VLA object's lifetime begins, not when execution reaches the
opening "{", but when it reaches the object definition.
[...]
--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar
Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 08:50 +0100
Re: Two questions on arrays with size defined by variables Andrey Tarasevich <noone@noone.net> - 2025-02-09 00:06 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 10:54 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 02:25 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:17 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 16:38 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 03:35 +0100
Re: Two questions on arrays with size defined by variables James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-09 23:03 -0500
Re: Two questions on arrays with size defined by variables Andrey Tarasevich <noone@noone.net> - 2025-02-09 20:14 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 07:43 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 22:57 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 19:33 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-10 14:17 -0800
Re: Two questions on arrays with size defined by variables Michael S <already5chosen@yahoo.com> - 2025-02-09 12:39 +0200
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:18 +0100
Re: Two questions on arrays with size defined by variables Michael S <already5chosen@yahoo.com> - 2025-02-09 19:57 +0200
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 19:10 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 16:46 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 02:56 +0100
Re: Two questions on arrays with size defined by variables antispam@fricas.org (Waldek Hebisch) - 2025-02-09 14:29 +0000
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:19 +0100
Re: Two questions on arrays with size defined by variables Andrey Tarasevich <noone@noone.net> - 2025-02-09 09:29 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:46 +0100
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:53 +0100
Re: Two questions on arrays with size defined by variables James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-09 15:55 -0500
Re: Two questions on arrays with size defined by variables antispam@fricas.org (Waldek Hebisch) - 2025-02-10 01:36 +0000
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 03:01 +0100
Re: Two questions on arrays with size defined by variables David Brown <david.brown@hesbynett.no> - 2025-02-10 11:39 +0100
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 18:57 +0100
Re: Two questions on arrays with size defined by variables David Brown <david.brown@hesbynett.no> - 2025-02-10 19:19 +0100
Re: Two questions on arrays with size defined by variables Michael S <already5chosen@yahoo.com> - 2025-02-09 20:19 +0200
Re: Two questions on arrays with size defined by variables Opus <ifonly@youknew.org> - 2025-02-10 02:44 +0100
Re: Two questions on arrays with size defined by variables Michael S <already5chosen@yahoo.com> - 2025-02-10 12:38 +0200
Re: Two questions on arrays with size defined by variables Opus <ifonly@youknew.org> - 2025-02-10 23:08 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 15:50 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 03:12 +0100
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 07:27 +0100
Re: Two questions on arrays with size defined by variables Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-02-09 22:49 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-10 19:14 +0100
Re: Two questions on arrays with size defined by variables Andrey Tarasevich <noone@noone.net> - 2025-02-09 07:15 -0800
Re: Two questions on arrays with size defined by variables Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-02-09 18:20 +0100
Re: Two questions on arrays with size defined by variables James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-09 15:34 -0500
Re: Two questions on arrays with size defined by variables James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-09 15:27 -0500
Re: Two questions on arrays with size defined by variables James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-02-09 15:16 -0500
Re: Two questions on arrays with size defined by variables Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-02-15 08:19 -0800
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