Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #86128

Re: “Why do arrays start at 0?"

Path csiph.com!news.mixmin.net!eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups comp.lang.fortran, comp.lang.c++
Subject Re: “Why do arrays start at 0?"
Date Sat, 27 Aug 2022 22:07:27 -0700
Organization None to speak of
Lines 39
Message-ID <878rn9j6r4.fsf@nosuchdomain.example.com> (permalink)
References <tebblf$2gpm$1@dont-email.me> <tedr4l$1cc0$1@gioia.aioe.org> <tedt6n$757$1@gioia.aioe.org> <tee5i3$cqm$4@newsreader4.netcologne.de> <teeo2r$8tl$1@gioia.aioe.org>
MIME-Version 1.0
Content-Type text/plain; charset=utf-8
Content-Transfer-Encoding 8bit
Injection-Info reader01.eternal-september.org; posting-host="c4eb9558376fc13f96f34a0aea0355d2"; logging-data="592493"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18cr1jAW4+hJCYsYMdHR4PW"
User-Agent Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux)
Cancel-Lock sha1:oaX9R0usvECw7ROorkgRVgicRyw= sha1:L8g+Cb4rtz54z6STOz2ga61G41I=
Xref csiph.com comp.lang.fortran:73536 comp.lang.c++:86128

Cross-posted to 2 groups.

Show key headers only | View raw

Lynn McGuire <lynnmcguire5@gmail.com> writes:
> On 8/27/2022 5:24 PM, Thomas Koenig wrote:
>> Lynn McGuire <lynnmcguire5@gmail.com> schrieb:
>>> On 8/27/2022 2:26 PM, Fred. Zwarts wrote:
>>>> Op 26.aug..2022 om 22:49 schreef Lynn McGuire:
>>>>> “Why do arrays start at 0?"
>>>>>      https://buttondown.email/hillelwayne/archive/why-do-arrays-start-at-0/
>>>>>
>>>>> "It's not the reason you think. No, it's not that reason either.”
>>>>>
>>>>> My Fortran starts at one.  My C++ starts at zero.  This has made my
>>>>> life hell.
>>>>
>>>> I assumed that it was done because in C x[i] is equivalent to *(x+i).
>>>
>>> Yup.  So Fortran x(i) is equivalent to *(x+i-1).
>> To be more precise, x(i) is equivalent to *(x+i-lbound(x,1))
>> 
>>> Or, the x is
>>> subtracted from first: x--; *(x+i);.
>> That's an f2c idiom, which is not valid C, AFAIK, because
>> the pointer would point before the actual array.
>
> While the second pointer is a bad pointer, it is not a illegal
> pointer. Variables can point to anywhere, they are not illegal until
> referenced. Otherwise, code would be crashing all over the place.  If
> I malloc'd some space, then free'd the space, and did not NULL the
> pointer, that dangling pointer would crash if ever referenced
> (hopefully) but not if it just hangs around.

Computing a pointer before the beginning of an array causes undefined
behavior in C and C++, even if you never dereference it.

[...]

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */

Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

“Why do arrays start at 0?" Lynn McGuire <lynnmcguire5@gmail.com> - 2022-08-26 15:49 -0500
  Re: “Why do arrays start at 0?" Gary Scott <garylscott@sbcglobal.net> - 2022-08-26 16:56 -0500
    Re: “Why do arrays start at 0?" Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-08-27 00:46 +0100
      Re: “Why do arrays start at 0?" d thiebaud <thiebauddick2@aol.com> - 2022-08-26 22:29 -0400
        Re: “Why do arrays start at 0?" Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-08-26 22:05 -0700
          Re: “Why do arrays start at 0?" Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-08-27 12:06 +0100
    Re: Re: “Why do arrays start at 0?" scott@slp53.sl.home (Scott Lurndal) - 2022-08-27 14:28 +0000
  Re: “Why do arrays start at 0?" Louis Krupp <lkrupp@invalid.pssw.com.invalid> - 2022-08-26 16:08 -0600
  Re: “Why do arrays start at 0?" Gawr Gura <gawrgura@mail.hololive.com> - 2022-08-26 15:18 -0700
  Re: “Why do arrays start at 0?" Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-08-27 00:44 +0100
  Re: “Why do arrays start at 0?" Thomas Koenig <tkoenig@netcologne.de> - 2022-08-27 05:47 +0000
    Re: “Why do arrays start at 0?" d thiebaud <thiebauddick2@aol.com> - 2022-08-27 15:19 -0400
      Re: “Why do arrays start at 0?" Thomas Koenig <tkoenig@netcologne.de> - 2022-08-27 22:22 +0000
  Re: “Why do arrays start at 0?" "Fred. Zwarts" <F.Zwarts@KVI.nl> - 2022-08-27 21:26 +0200
    Re: “Why do arrays start at 0?" Lynn McGuire <lynnmcguire5@gmail.com> - 2022-08-27 15:01 -0500
      Re: “Why do arrays start at 0?" Thomas Koenig <tkoenig@netcologne.de> - 2022-08-27 22:24 +0000
        Re: “Why do arrays start at 0?" Lynn McGuire <lynnmcguire5@gmail.com> - 2022-08-27 22:40 -0500
          Re: “Why do arrays start at 0?" Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-08-27 22:07 -0700
          Re: “Why do arrays start at 0?" Thomas Koenig <tkoenig@netcologne.de> - 2022-08-28 07:50 +0000
            Re: “Why do arrays start at 0?" David Brown <david.brown@hesbynett.no> - 2022-08-28 11:52 +0200
          Re: “Why do arrays start at 0?" Paavo Helde <eesnimi@osa.pri.ee> - 2022-08-28 19:43 +0300
      Re: “Why do arrays start at 0?" "Fred. Zwarts" <F.Zwarts@KVI.nl> - 2022-08-28 10:01 +0200
        Re: “Why do arrays start at 0?" Thomas Koenig <tkoenig@netcologne.de> - 2022-08-28 08:14 +0000
  Re: “Why do arrays start at 0?" Bonita Montero <Bonita.Montero@gmail.com> - 2022-08-28 11:07 +0200
  Re: ???Why do arrays start at 0?" Juha Nieminen <nospam@thanks.invalid> - 2022-08-29 11:15 +0000

csiph-web