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Groups > comp.lang.c > #110312
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Help on this typedef |
| Date | 2017-05-18 09:35 -0700 |
| Organization | None to speak of |
| Message-ID | <lnwp9e15td.fsf@kst-u.example.com> (permalink) |
| References | (4 earlier) <faaaf47a-51ec-4323-aba2-18cabef07fe8@googlegroups.com> <kfnd1bcsb3d.fsf@x-alumni2.alumni.caltech.edu> <7828b0dd-de46-40a2-9636-81117d1f17f6@googlegroups.com> <kfninl2nqqy.fsf@x-alumni2.alumni.caltech.edu> <799899ab-ccf3-49a4-a928-d405dc142fff@googlegroups.com> |
joel.rees@gmail.com writes:
> On Monday, May 15, 2017 at 11:23:23 PM UTC+9, Tim Rentsch wrote:
[...]
>> Ah. In that case I must demur regarding part of your later
>> statement. An access through an array type of extent 1 is
>> not definedly allowed to access elements after the element
>> at index 0.
>
> typedef string_header_s struct
> { short length; /* limited length */
> char text[ 1 ];
> } string_header_t;
That's called the "struct hack", and it was always of questionable
validity. You can likely get away with allocating extra memory and
referring to, for example, obj.text[10], but the behavior is undefined.
C99 introduced flexible array members, described in N1570 6.7.2.1p18,
as a well-defined replacement for the struct hack. See also question
2.6 of the comp.lang.c FAQ, <http://c-faq.com/>.
> And before you C++ types came around, we just left the array size
> out: char text[]. But that was declared in all cases to be equivalent
> to char *, so it means something else, now. And if that's what you
> mean in such a header, you say char *, instead.
Prior to C99's instroduction of flexible array members, defining a
struct member as `char text[]` was invalid.
And no, `char text[]` is in no way equivalent to `char *text`. See
section 6 of the comp.lang.c FAQ.
You can define a pointer member, but then you have to allocate memory
for it to point to. With an array member, the memory is allocated
within the struct object itself.
[...]
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Help on this typedef fl <rxjwg98@gmail.com> - 2017-05-10 19:12 -0700
Re: Help on this typedef Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2017-05-10 21:06 -0600
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-10 20:11 -0700
Re: Help on this typedef David Brown <david.brown@hesbynett.no> - 2017-05-11 10:03 +0200
Re: Help on this typedef supercat@casperkitty.com - 2017-05-11 08:35 -0700
Re: Help on this typedef David Brown <david.brown@hesbynett.no> - 2017-05-12 10:34 +0200
Re: Help on this typedef joel.rees@gmail.com - 2017-05-12 06:01 -0700
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-12 09:38 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-12 05:08 -0700
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-13 14:25 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-14 23:36 -0700
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-15 07:23 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-18 07:40 -0700
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-18 09:35 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-18 10:59 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-18 23:40 -0700
Re: Help on this typedef jadill33@gmail.com - 2017-05-19 08:12 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 08:41 -0700
Re: Help on this typedef jadill33@gmail.com - 2017-05-19 09:41 -0700
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-19 09:34 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 10:18 -0700
Re: Help on this typedef Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-19 21:35 +0100
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 14:16 -0700
Re: Help on this typedef Ike Naar <ike@iceland.freeshell.org> - 2017-05-19 21:15 +0000
Re: Help on this typedef Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-19 23:54 +0100
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-19 14:25 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 15:18 -0700
Re: Help on this typedef Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-19 23:52 +0100
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-19 16:42 -0700
Re: Help on this typedef Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-20 01:16 +0100
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-20 01:58 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-20 02:25 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-19 22:09 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 23:23 -0700
Re: Help on this typedef "James R. Kuyper" <jameskuyper@verizon.net> - 2017-05-19 13:33 -0400
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 13:44 -0700
Re: Help on this typedef jameskuyper@verizon.net - 2017-05-19 19:20 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 23:30 -0700
Re: Help on this typedef jameskuyper@verizon.net - 2017-05-20 07:20 -0700
Re: Help on this typedef jameskuyper@verizon.net - 2017-05-20 07:46 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-22 10:50 -0700
Re: Help on this typedef "James R. Kuyper" <jameskuyper@verizon.net> - 2017-05-18 12:37 -0400
Re: Help on this typedef Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-18 20:02 +0100
Re: Help on this typedef joel.rees@gmail.com - 2017-05-19 00:20 -0700
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-19 09:51 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-19 10:31 -0700
Re: Help on this typedef Ike Naar <ike@iceland.freeshell.org> - 2017-05-19 19:48 +0000
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-20 08:47 -0700
Re: Help on this typedef "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-05-27 18:50 +0200
Re: Help on this typedef joel.rees@gmail.com - 2017-05-12 06:17 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-12 08:46 -0700
Re: Help on this typedef joel.rees@gmail.com - 2017-05-12 18:11 -0700
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-12 18:37 -0700
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-13 09:44 -0700
Re: Help on this typedef Keith Thompson <kst-u@mib.org> - 2017-05-13 13:47 -0700
Re: Help on this typedef Robert Wessel <robertwessel2@yahoo.com> - 2017-05-14 00:28 -0500
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-14 13:39 -0700
Re: Help on this typedef raltbos@xs4all.nl (Richard Bos) - 2017-05-15 13:02 +0000
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-15 07:30 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-12 20:45 -0700
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-13 09:57 -0700
Re: Help on this typedef Philip Lantz <prl@canterey.us> - 2017-05-13 12:07 -0700
Re: Help on this typedef David Brown <david.brown@hesbynett.no> - 2017-05-14 15:34 +0200
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-14 12:48 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-15 07:39 -0700
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-24 08:23 -0700
Re: Help on this typedef supercat@casperkitty.com - 2017-05-24 09:17 -0700
Re: Help on this typedef Tim Rentsch <txr@alumni.caltech.edu> - 2017-05-27 06:15 -0700
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