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Re: Why are VLAs optional in C11?

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Am 18.08.2012 06:04, schrieb John Nagle:
>    True.  Here are some of the known problems with VLAs:
> 

-- snip --

> - The semantics of VLA parameters is painful.

true, but you yourself with your proposal of reference show a way out
of that, that would make them bearable

>  They're
> automatically reduced to pointers, with the length information
> lost.  "sizeof" returns the size of a pointer.

technically not true, or only half the truth

only the size for innermost dimension is lost, the other dimensions
come accross and are perfectly accessible through sizeof. The first
dimension (as a sizeof expression) is usually not needed for the
computation inside the function.

And the reason that this dimension is lost is not the fault of VLA,
this dimension is lost for all "array" parameters.

Most disadvantages of VLA disappear if you just use pointers to VLA.

double (*A)[n][m] = malloc(sizeof(double[n][m]));

is easy to read, keeps track of both dimensions, is checkable for
allocation problems and is in no risk of smashing the stack.

If you want to introduce references à-la C++ to make the *use* of them
easier, this would be a strong argument for them.

+++

I have to observe that you reply here in this thread and not in the
other one where I gave you a detailed analysis of your proposal and
where I basically think I have proven that with your proposal you are
doing VLA (or more precisely VM types) anyhow.

Since this is already the second time, should I conclude that you are
more interested in VLA-bashing than in taking your own proposal
forward?

Jens

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Thread

Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-17 15:42 -0700
  Re: Why are VLAs optional in C11? Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-18 01:19 +0200
    Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-17 16:23 -0700
      Re: Why are VLAs optional in C11? Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-18 10:12 +0200
    Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-17 21:04 -0700
      Re: Why are VLAs optional in C11? pacman@kosh.dhis.org (Alan Curry) - 2012-08-18 05:34 +0000
        Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-17 23:07 -0700
          Re: Why are VLAs optional in C11? pacman@kosh.dhis.org (Alan Curry) - 2012-08-18 08:29 +0000
            Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-18 09:37 -0700
              Re: Why are VLAs optional in C11? pa@see.signature.invalid (Pierre Asselin) - 2012-08-19 02:27 +0000
            Re: Why are VLAs optional in C11? Ike Naar <ike@sverige.freeshell.org> - 2012-08-18 17:49 +0000
      Re: Why are VLAs optional in C11? Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-18 08:32 +0200
      Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-18 02:50 -0700
      Re: Why are VLAs optional in C11? jacob navia <jacob@spamsink.net> - 2012-08-18 14:33 +0200
        Re: Why are VLAs optional in C11? Ike Naar <ike@sverige.freeshell.org> - 2012-08-18 13:23 +0000
        Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-18 13:48 -0700
          Re: Why are VLAs optional in C11? jacob navia <jacob@spamsink.net> - 2012-08-18 23:31 +0200
            Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-18 18:14 -0700
              Re: Why are VLAs optional in C11? jacob navia <jacob@spamsink.net> - 2012-08-19 09:38 +0200
                Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-19 03:07 -0700
                Re: Why are VLAs optional in C11? jacob navia <jacob@spamsink.net> - 2012-08-19 12:29 +0200
                Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-19 10:38 -0700
                Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-19 13:14 -0700
                Re: Why are VLAs optional in C11? Keith Thompson <kst-u@mib.org> - 2012-08-19 13:59 -0700
                Re: Why are VLAs optional in C11? Owen Shepherd <nntp@owenshepherd.net> - 2012-08-27 22:17 +0100
                Re: Why are VLAs optional in C11? Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-28 00:34 +0200
                Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-27 19:36 -0700
                Re: Why are VLAs optional in C11? James Kuyper <jameskuyper@verizon.net> - 2012-08-27 22:54 -0400
                Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-27 22:39 -0700
        Re: Why are VLAs optional in C11? "pdx_scooter@yahoo.com" <pdx_scooter@yahoo.com> - 2022-10-01 13:15 -0700
          Re: Why are VLAs optional in C11? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-10-01 14:33 -0700
          Re: Why are VLAs optional in C11? Tomasz Stanislawski <stanislawski.tomasz@googlemail.com> - 2023-01-25 04:21 -0800
  Re: Why are VLAs optional in C11? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-17 20:54 -0400
  Re: Why are VLAs optional in C11? John Nagle <nagle@animats.com> - 2012-08-17 20:56 -0700

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