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| From | Steve Thompson <stevet810@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Compatibility question |
| Date | 2012-10-21 23:04 +0000 |
| Organization | Friends of the Galactic Collective |
| Message-ID | <r0uOpC.2t0.omMVr@gmail.com> (permalink) |
| References | <Li3Gtk.7Rk.IPeax@gmail.com> <aeejkmFnpi3U11@mid.individual.net> <0.a54a7a03bedb5e053e7b.20121020115019BST.87d30d1kpg.fsf@bsb.me.uk> <lnlif1gf5m.fsf@nuthaus.mib.org> |
On Sat, Oct 20, 2012 at 11:41:09AM -0700, Keith Thompson wrote:
> 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.)
The p[1] form is a bit of an eyesore since the actual structure I am
using may have its "data area" appended to the structure, or it may be
somewhere else.
> If you're concerned about C90 compatility, you'll need to decide which
> form is more portable *to the compilers you're using*.
I would have preferred to maintain compatibility with older compilers,
but I am finding that some modern features are necessary for my
application. Nothing is yet carved in stone; my application might be
able to function without POSIX threads in a hypothetical lobotomized
version, but I won't know until I'm further along. Part of it is a
library, and of course many of the functions have nothing to do with
thread operations, so there may be a case for maintaining a certain
degree of compatibility.
Regards,
Steve Thompson
--
GOTO's are like guns. Safety is entirely contingent on the user.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
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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