Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c > #124032
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: NULL as the empty string |
| Date | 2017-12-08 16:05 -0800 |
| Organization | None to speak of |
| Message-ID | <lnr2s4sr4c.fsf@kst-u.example.com> (permalink) |
| References | (4 earlier) <p0etae$tqd$1@dont-email.me> <lnzi6trkxz.fsf@kst-u.example.com> <p0f1eb$sg1$1@dont-email.me> <lnvahgst7s.fsf@kst-u.example.com> <p0f7ki$6t5$1@dont-email.me> |
jacobnavia <jacob@jacob.remcomp.fr> writes:
> Le 09/12/2017 à 00:19, Keith Thompson a écrit :
>> Since the cases we're talking about have undefined behavior, a
>> conforming implementation can behave as you propose. Does lcc-win
>> do this? If not, are you planning to change it so it does?
>
> Maybe, depends on the pros /cons I see in this discussion. Since any use
> of NULL in strings is undefined behavior now, I have free hand to do
> anything. I proposed the following truth table:
>
> strlen(str)
>
> The same behavior. For non NULL pointers nothing changes.
>
> strlen(NULL) --> 0.
>
> For strcat:
>
> strcat(str,str) --> the same
> strcat(str,NULL) -> No-Op. Returns str
> strcat(NULL, str); -> No-Op, returns NULL.
>
> Now, it would be needed to change the definition of a string. A string
> is either a pointer to an array of zero terminated chars, or NULL,
> meaning the empty string.
The current definitions (N1570 7.1.1.p1) are:
A *string* is a contiguous sequence of characters terminated by and
including the first null character.
[...]
A *pointer to a string* is a pointer to its initial (lowest
addressed) character.
So a string is not a pointer, and a pointer cannot be a string.
Are you proposing to change the definition so that there's no
distinction between a "string" and a "pointer to a string"? What then
would we call the sequence of characters that's currently defined as a
"string"? If such a change were to be made to the standard, it would
require changing the wording for every function that acts on strings.
> There are then two representations for the empty string:
>
> NULL or "\0"
You keep referring to NULL (the name of a macro) when you mean the null
pointer. That's exactly the point that caused the confusion in the
first place.
The way I would describe your proposal is that a null pointer is to be
treated as if it were a pointer to an empty string. (I'm not sure
whether it would make sense to say that a null pointer actually points
to an empty string. If so, I'm having difficulty coming up with a
revised definition of "string", since a null pointer does not physically
point to anything. It might do so on a system where memory address 0
contains a readable 0 bytes, but it would be impractical for the
standard to require that.)
[...]
--
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"
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-21 23:52 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-11-21 15:16 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-22 00:38 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-11-21 16:02 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-22 01:13 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-11-21 16:52 -0800
Re: NULL as the empty string Robert Wessel <robertwessel2@yahoo.com> - 2017-11-21 18:09 -0600
Re: NULL as the empty string Siri Cruise <chine.bleu@yahoo.com> - 2017-11-21 16:34 -0800
Re: NULL as the empty string David Brown <david.brown@hesbynett.no> - 2017-11-22 12:12 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-21 15:57 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-22 01:06 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-22 15:42 -0800
Re: NULL as the empty string Melzzzzz <Melzzzzz@zzzzz.com> - 2017-11-22 23:49 +0000
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-22 15:56 -0800
Re: NULL as the empty string Melzzzzz <Melzzzzz@zzzzz.com> - 2017-11-23 00:06 +0000
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-23 17:31 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-24 09:42 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-24 13:47 -0800
Re: NULL as the empty string Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-11-22 06:46 +0000
Re: NULL as the empty string John Bode <jfbode1029@gmail.com> - 2017-12-08 10:27 -0800
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-08 11:11 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-08 21:39 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-08 13:03 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-08 22:50 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-08 15:19 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-09 00:35 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-08 16:05 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-09 01:22 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-08 17:39 -0800
Re: NULL as the empty string John Bode <jfbode1029@gmail.com> - 2017-12-11 12:22 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-09 01:29 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-08 17:47 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-09 07:05 +0100
Re: NULL as the empty string David Brown <david.brown@hesbynett.no> - 2017-12-09 18:37 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-09 11:53 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-12 10:49 -0800
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-12 13:39 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-12 16:05 -0800
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-13 03:43 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-13 08:45 -0800
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-13 09:12 -0800
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-13 13:27 -0800
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-13 14:02 -0800
Re: NULL as the empty string asetofsymbols@gmail.com - 2017-12-13 14:58 -0800
Re: NULL as the empty string asetofsymbols@gmail.com - 2017-12-13 15:11 -0800
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-14 03:49 -0800
Re: NULL as the empty string mark.bluemel@gmail.com - 2017-12-14 04:05 -0800
Re: NULL as the empty string David Brown <david.brown@hesbynett.no> - 2017-12-14 13:09 +0100
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-14 05:02 -0800
Re: NULL as the empty string David Brown <david.brown@hesbynett.no> - 2017-12-14 14:54 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-14 07:38 -0800
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-14 09:50 -0800
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-14 09:20 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-14 09:53 -0800
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-14 12:57 -0800
Re: NULL as the empty string herrmannsfeldt@gmail.com - 2017-12-14 17:22 -0800
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-14 17:26 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-08 21:23 +0100
Re: NULL as the empty string Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-12-08 13:41 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-08 22:54 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-21 15:17 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-22 00:26 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-11-21 16:03 -0800
Re: NULL as the empty string "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 00:27 +0100
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-22 00:42 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-11-21 16:05 -0800
Re: NULL as the empty string herrmannsfeldt@gmail.com - 2017-12-06 22:33 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-07 12:04 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-07 23:20 +0100
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-07 15:04 -0800
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-11-21 15:28 -0800
Re: NULL as the empty string Thiago Adams <thiago.adams@gmail.com> - 2017-11-21 16:04 -0800
Re: NULL as the empty string Siri Cruise <chine.bleu@yahoo.com> - 2017-11-21 16:25 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-11-22 01:34 +0100
Re: NULL as the empty string bartc <bc@freeuk.com> - 2017-11-22 00:36 +0000
Re: NULL as the empty string Öö Tiib <ootiib@hot.ee> - 2017-11-21 23:07 -0800
NULL as the empty string asetofsymbols@gmail.com - 2017-11-23 22:23 -0800
Re: NULL as the empty string Geoff <geoff@invalid.invalid> - 2017-12-09 09:05 -0800
Re: NULL as the empty string Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2017-12-09 12:40 -0500
Re: NULL as the empty string gordonb.yj0bc@burditt.org (Gordon Burditt) - 2017-12-09 13:50 -0600
Re: NULL as the empty string Ian Collins <ian-news@hotmail.com> - 2017-12-10 08:59 +1300
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-09 12:22 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-11 01:42 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-10 19:20 -0800
Re: NULL as the empty string jacobnavia <jacob@jacob.remcomp.fr> - 2017-12-11 18:56 +0100
Re: NULL as the empty string Keith Thompson <kst-u@mib.org> - 2017-12-11 11:19 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-15 09:29 -0800
Re: NULL as the empty string Thiago Adams <thiago.adams@gmail.com> - 2018-01-05 08:28 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2018-01-05 09:37 -0800
Re: NULL as the empty string Thiago Adams <thiago.adams@gmail.com> - 2018-01-05 17:08 -0800
Re: NULL as the empty string supercat@casperkitty.com - 2017-12-15 09:18 -0800
csiph-web