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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Compatibility question |
| Date | 2012-10-20 11:41 -0700 |
| Organization | None to speak of |
| Message-ID | <lnlif1gf5m.fsf@nuthaus.mib.org> (permalink) |
| References | <Li3Gtk.7Rk.IPeax@gmail.com> <aeejkmFnpi3U11@mid.individual.net> <0.a54a7a03bedb5e053e7b.20121020115019BST.87d30d1kpg.fsf@bsb.me.uk> |
Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> Ian Collins <ian-news@hotmail.com> writes:
>> On 10/20/12 16:08, Steve Thompson wrote:
>>> I have been using structures containing zero-length arrays as a means
>>> of combining descriptors and array data in a single allocation unit.
>>> Something like the following is a common idiom:
>>>
>>> struct foo {
>>> int a, b;
>>> size_t len;
>>> char p[0];
>>> };
>>
>> That should really be
>>
>> char p[];
>>
>> Which is the standardised (as of C99) form of the struct hack.
>>
>>> So far, so good. My questions regards the availability of zero-length
>>> arrays in common systems. That is, if I wish my code to be compatible
>>> with most C compilers in use today, should I worry about avoiding
>>> zero-length arrays, or is the feature old enough, with sufficient
>>> prevalence to make it's use reasonable in portable code?
>>
>> Most compilers should support the standard form, or the zero length
>> array form of the struct hack.
>
> Before C99, the usual form was a one-element array -- a small amount of
> waste, but guaranteed to compile everywhere. A zero-length array is a
> constraint violation so, of the three options (p[], p[1] and p[0]) it is
> the most likely to give a compiler stomach ache.
>
> Lots of part of C99 (such as // comments) are nearly ubiquitous, even in
> the Microsoft world, but I don't know how wide-spread p[] is.
Microsoft's C compiler, which is notorious for its lack of C99 support,
does support flexible array members -- but only if you enable "language
extensions". (I'm using Microsoft Visual C++ 2010 Express.)
So my advice is to go ahead and use the C99 feature p[] in preference to
either p[0] (which is a constraint violation in C90, C99, and C11) or
p[1] (which is a valid declaration, but accessing elements past p[0],
strictly speaking, has undefined behavior.)
If you're concerned about C90 compatility, you'll need to decide which
form is more portable *to the compilers you're using*.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Will write code for food.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-20 03:08 +0000
Re: Compatibility question Ian Collins <ian-news@hotmail.com> - 2012-10-20 16:20 +1300
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-20 11:50 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-20 11:41 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-21 23:04 +0000
Re: Compatibility question Barry Schwarz <schwarzb@dqel.com> - 2012-10-21 20:27 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-20 04:01 +0000
Re: Compatibility question Ian Collins <ian-news@hotmail.com> - 2012-10-21 09:26 +1300
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-21 22:54 +0000
Re: Compatibility question Ian Collins <ian-news@hotmail.com> - 2012-10-22 12:29 +1300
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-21 23:50 +0000
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-22 02:27 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 02:28 +0000
Re: Compatibility question Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-22 11:18 -0400
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 16:19 +0000
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-22 17:37 +0100
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-22 17:40 +0100
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-22 17:30 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 17:23 +0000
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-22 10:52 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 18:42 +0000
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-22 21:06 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 22:52 +0000
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-23 03:33 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-23 12:28 +0000
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-23 16:45 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-23 17:53 +0000
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-23 12:41 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-23 21:28 +0100
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-23 20:57 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-23 12:26 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-23 20:39 +0000
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-23 15:53 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-24 00:57 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-23 20:06 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-24 11:18 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-24 12:04 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-24 23:10 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-24 16:58 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-25 01:46 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-24 19:40 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-24 20:20 +0000
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-24 14:38 -0700
Re: Compatibility question James Kuyper <jameskuyper@verizon.net> - 2012-10-24 17:55 -0400
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-24 16:29 -0700
Re: Compatibility question Greg Martin <greg@softsprocket.com> - 2012-10-24 15:21 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-26 03:30 +0000
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-26 13:02 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-27 00:04 +0000
Re: Compatibility question Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-27 20:15 +0100
Re: Compatibility question Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-10-27 16:36 -0600
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-28 17:36 +0000
Re: Compatibility question Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-10-27 22:42 +0300
Re: Compatibility question Greg Martin <greg@softsprocket.com> - 2012-10-27 14:30 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-27 22:57 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-27 17:04 -0700
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-27 17:14 -0700
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-27 18:04 -0700
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-24 16:46 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-25 01:18 +0000
Re: Compatibility question Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-10-27 21:08 +0300
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-28 17:38 +0000
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-23 00:38 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-22 16:50 -0700
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-23 12:33 +0000
Re: Compatibility question Öö Tiib <ootiib@hot.ee> - 2012-10-22 14:23 -0700
Re: Compatibility question James Kuyper <jameskuyper@verizon.net> - 2012-10-22 17:26 -0400
Re: Compatibility question Ian Collins <ian-news@hotmail.com> - 2012-10-23 10:55 +1300
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 23:27 +0000
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-22 22:44 +0100
Re: Compatibility question Les Cargill <lcargill99@comcast.com> - 2012-10-22 17:15 -0500
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-23 00:13 +0100
Re: Compatibility question James Kuyper <jameskuyper@verizon.net> - 2012-10-22 18:35 -0400
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-23 00:14 +0100
Re: Compatibility question Steve Thompson <stevet810@gmail.com> - 2012-10-22 23:42 +0000
Re: Compatibility question Ian Collins <ian-news@hotmail.com> - 2012-10-23 13:35 +1300
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-22 17:01 -0700
Re: Compatibility question "BartC" <bc@freeuk.com> - 2012-10-23 01:47 +0100
Re: Compatibility question Keith Thompson <kst-u@mib.org> - 2012-10-21 19:27 -0700
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