Re: Two questions on arrays with size defined by variables

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From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: Two questions on arrays with size defined by variables
Date	Sat, 15 Feb 2025 08:19:10 -0800
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Andrey Tarasevich <noone@noone.net> writes:

> On Sat 2/8/2025 11:50 PM, Janis Papanagnou wrote:
>
>> I've found examples on the Net where the arrays have been defined
>> in a function context and the size passed as parameter
>>
>>    f(int n) {
>>       char * arr[n];
>>       ...
>>    }
>
> Yes, that would be a VLA.
>
>> That reminded me on other languages where you'd need at least a
>> block context for dynamically sized arrays, like
>>
>>    int n = 5;
>>    {
>>       char * arr[n];
>>       ...
>>    }
>
> But a function body is in itself a block.  Inside a function body
> you are already in "a block context".
>
>> Anyway.  I tried it without function or block context
>>
>>    int n = 5;
>>    char * arr[n];
>>    ...
>>
>> and it seemed to work seamlessly like that (with GNU cc,
>> -std=C99).
>
> You mean you did this at file scope?  No, VLAs are illegal at file
> scope.  And I was unable to repeat this feat in GCC.
>
>> Q1:  Is this a correct (portable) form?
>
> VLA objects have to be declared locally.  However, keep in mind
> that support for local declarations of VLA _objects_ is now
> optional (i.e. not portable).  Support for variably-modified
> _types_ themselves (VLA types) is mandatory.  But you are not
> guaranteed to be able to declare an actual VLA variable.

In regular English usage, there is no hyphen between "variably"
and "modified" in "variably modified types".  The reason for this
rule is "variably" is an adverb, and thus can pertain only to the
adjective "modified", and not to the noun "types".  A hyphen is
used only when needed to clarify ambiguity;  because there is no
ambiguity, there is no hyphen.

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Thread

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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