Re: Variable-length arrays: should they be used at all?

From	Ian Collins <ian-news@hotmail.com>
Newsgroups	comp.lang.c
Subject	Re: Variable-length arrays: should they be used at all?
Date	2012-06-28 09:35 +1200
Message-ID	<a51cldFtntU2@mid.individual.net> (permalink)
References	<jscgum$lk6$1@speranza.aioe.org> <kfnvcic4nxi.fsf@x-alumni2.alumni.caltech.edu>

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On 06/28/12 06:20 AM, Tim Rentsch wrote:
>
> There are two distinct concerns here.  Let's take them one at a
> time.
>
> First, encountering a VLA declaration during execution may blow
> the stack and crash, and there is no portable way to detect or
> deal with that.  However, it is easy for implementations to
> provide a way of doing that, without adding any new language
> constructs, as I explained in another posting.

<snip second>

> The flip side of the first concern is that, one, it often isn't a
> big deal in practice;  two, implementors should be encouraged to
> supply a mechanism for detecting/handling VLA allocation failure,
> since it is easy to provide such a mechanism;  and three, VLA
> support provides an important benefit that does not have the
> associated risk of undetectable allocation failure, namely,
> variably modified types and more specifically pointers to VLAs,
> which are useful even if VLA objects are never declared.

While the "easy to provide" may be true on some platforms, it will be 
false for others without memory management.  Even the easy 
implementations may come at a run time cost which negates the 
performance advantages of VLAs over dynamically allocated memory.

-- 
Ian Collins

Thread

Variable-length arrays: should they be used at all? Rui Maciel <rui.maciel@gmail.com> - 2012-06-26 15:28 +0100
  Re: Variable-length arrays: should they be used at all? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 11:54 -0400
  Re: Variable-length arrays: should they be used at all? jacob navia <jacob@spamsink.net> - 2012-06-26 21:05 +0200
    Re: Variable-length arrays: should they be used at all? Rui Maciel <rui.maciel@gmail.com> - 2012-06-26 21:04 +0100
      Re: Variable-length arrays: should they be used at all? Keith Thompson <kst-u@mib.org> - 2012-06-26 13:09 -0700
        Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-06-27 17:50 +1200
          Re: Variable-length arrays: should they be used at all? jacob navia <jacob@spamsink.net> - 2012-06-27 07:57 +0200
            Re: Variable-length arrays: should they be used at all? gwowen <gwowen@gmail.com> - 2012-06-27 00:49 -0700
            Re: Variable-length arrays: should they be used at all? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-27 13:50 +0100
              Re: Variable-length arrays: should they be used at all? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-27 10:21 -0400
                Re: Variable-length arrays: should they be used at all? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-27 19:56 +0100
          Re: Variable-length arrays: should they be used at all? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-06 00:55 +0300
            Re: Variable-length arrays: should they be used at all? Andrew Cooper <amc96@cam.ac.uk> - 2012-07-05 23:37 +0100
              Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-06 16:53 -0700
            Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-07-06 18:26 +1200
              Re: Variable-length arrays: should they be used at all? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-07 17:37 +0300
                Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-07-08 08:03 +1200
            Re: Variable-length arrays: should they be used at all? gwowen <gwowen@gmail.com> - 2012-07-06 02:58 -0700
              Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-06 18:11 -0700
                Re: Variable-length arrays: should they be used at all? gwowen <gwowen@gmail.com> - 2012-07-09 02:33 -0700
                Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-09 11:35 -0700
                Re: Variable-length arrays: should they be used at all? Ike Naar <ike@iceland.freeshell.org> - 2012-07-09 22:33 +0000
                Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-10 10:52 -0700
                Re: Variable-length arrays: should they be used at all? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-07-09 12:03 -0700
                Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-07-10 09:19 +1200
        Re: Variable-length arrays: should they be used at all? Gareth Owen <gwowen@gmail.com> - 2012-06-27 07:25 +0100
    Re: Variable-length arrays: should they be used at all? jacob navia <jacob@spamsink.net> - 2012-06-27 07:10 +0200
      Re: Variable-length arrays: should they be used at all? jacob navia <jacob@spamsink.net> - 2012-06-27 20:48 +0200
  Re: Variable-length arrays: should they be used at all? Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 21:13 +0200
    Re: Variable-length arrays: should they be used at all? Rui Maciel <rui.maciel@gmail.com> - 2012-06-26 20:47 +0100
      Re: Variable-length arrays: should they be used at all? Keith Thompson <kst-u@mib.org> - 2012-06-26 13:05 -0700
      Re: Variable-length arrays: should they be used at all? David Resnick <lndresnick@gmail.com> - 2012-06-26 13:51 -0700
        Re: Variable-length arrays: should they be used at all? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-26 17:10 -0700
        Re: Variable-length arrays: should they be used at all? Gareth Owen <gwowen@gmail.com> - 2012-06-27 07:27 +0100
        Re: Variable-length arrays: should they be used at all? Rui Maciel <rui.maciel@gmail.com> - 2012-06-27 20:23 +0100
  Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 11:20 -0700
    Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-06-28 09:35 +1200
      Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 17:23 -0700
        Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-06-28 13:06 +1200
          Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 10:48 -0700
            Re: Variable-length arrays: should they be used at all? Ian Collins <ian-news@hotmail.com> - 2012-06-30 21:58 +1200
              Re: Variable-length arrays: should they be used at all? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-30 03:37 -0700
              Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-01 19:31 -0700
            Re: Variable-length arrays: should they be used at all? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-06 00:54 +0300
              Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-06 17:58 -0700
        Re: Variable-length arrays: should they be used at all? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-06 00:49 +0300
          Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-06 16:38 -0700
            Re: Variable-length arrays: should they be used at all? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-07 18:00 +0300
              Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-07 12:40 -0700
                Re: Variable-length arrays: should they be used at all? pacman@kosh.dhis.org (Alan Curry) - 2012-07-08 02:54 +0000
                Re: Variable-length arrays: should they be used at all? jacob navia <jacob@spamsink.net> - 2012-07-08 13:33 +0200
                Re: Variable-length arrays: should they be used at all? pacman@kosh.dhis.org (Alan Curry) - 2012-07-08 22:18 +0000
                Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-09 10:57 -0700
                Re: Variable-length arrays: should they be used at all? pacman@kosh.dhis.org (Alan Curry) - 2012-07-09 21:38 +0000
                Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-10 11:12 -0700
                Re: Variable-length arrays: should they be used at all? Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-08 11:28 -0700

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