Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | jacob navia <jacob@spamsink.net> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Variable-length arrays: should they be used at all? |
| Date | 2012-06-26 21:05 +0200 |
| Organization | lccwin |
| Message-ID | <jsd15l$28f$1@speranza.aioe.org> (permalink) |
| References | <jscgum$lk6$1@speranza.aioe.org> |
Le 26/06/12 16:28, Rui Maciel a écrit :
> In the thread "Learning C as an existing programmer", an interesting
> discussion arose over the use of variable-length arrays (VLAs), specifically
> the dangers they pose by not providing a way to detect potential memory
> allocation bugs.
>
> GCC's page on variable-length arrays says nothing about what to expect when
> a VLA is too large to handle.[1] In addition, what has been said in GCC's
> mailing list about avoiding segfaults induced by huge VLAs isn't very
> reassuring.[2]
>
> With this in mind, and considering that VLAs were made optional in C11, is
> it a good idea to simply refuse using them?
>
>
> Rui Maciel
>
> [1] http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html
> [2] http://gcc.gnu.org/ml/gcc/2007-01/msg00179.html
>
VLAs are indispensable when you want to avoid unnecessary calls
to the expensive malloc function.
For instance if you have some structure X that is hidden as an opaque
structure to avoid that client code
You can of course get the size of the hidden structure by calling a
library function.
Example:
int main(void)
{
char buffer[iList.GetSize(NULL)];
List *L = (List *)&buffer[0];
iList.InitList(L);
// Here you use your list.
iList.Clear(L);
/// Here you do not need to call iList.Finalize since
// you haven't allocated it with malloc
}
The crucial call here is:
char buffer[iList.GetSize(NULL)];
This allows tghe library to return the size of the structure WITHOUT
disclosing its internal state. This is very important.
The alternatives are very bad since you would have to
#define SIZEOF_LIST_HEADER 56
and do not forget to update that each time your List structure changes.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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
csiph-web