Re: How many wide characters may mbstowcs store?

From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: How many wide characters may mbstowcs store?
Date	2020-05-24 16:49 -0700
Organization	A noiseless patient Spider
Message-ID	<86ftbouc4k.fsf@linuxsc.com> (permalink)
References	<r9bd16$nbt$1@solani.org> <r9bobp$fg5$1@news.albasani.net> <r9boue$25k$2@solani.org> <86mu6exxpw.fsf@linuxsc.com> <n5guG.283633$Xk.216585@fx46.iad>

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scott@slp53.sl.home (Scott Lurndal) writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Philipp Klaus Krause <pkk@spth.de> writes:
>>
>>> Am 11.05.20 um 16:44 schrieb Bonita Montero:
>>>
>>>> There's a POSIX-extension that if you pass nullptr for s, you get
>>>> the size of the buffer needed for s.  Maybe this will help you.
>>>> Otherwise: multibyte-characters are usually UTF-8-characters and
>>>> it should be easy to find code to convert these charaters into
>>>> wide-characters; but it should be also easy to write this yourself
>>>> in 20min.
>>>
>>> At the moment I want to figure out what to do about the problem.  File a
>>> bug against GCC in Ubuntu?  File a defect report / clarification request
>>> with WG14?
>>
>> File a gcc bug report.  The gnu/gcc folks have misunderstood the
>> standard, and they are shooting their users in the foot.  Your
>> support/regression tests deserve thanks, and have provided a
>> public service.
>
> It's not a bug.  The phrase
>
>     "No characters that follow a null byte (which is converted into
>      a wide-character code with value 0) shall be examined or converted."
>
> Is there to ensure that no bytes beyond the null are _read_ from the
> source string (thus ensuring that no page fault, for example, occurs
> because a byte beyond the nul is on the next (unallocated) page).
> It has no bearing on whether the function is allowed to write
> element 'n-1' of the destination operand which is allowed explictly
> by the standard regardless of the length of the input string.

I don't agree with your interpretation.  First you are misquoting
the description given in 7.22.8.1 p2.  Second the statements that
"[mbstowcs] stores not more than n wide characters into the
array" and that "No multibyte characters that follow a null
character [...] will be examined or converted" do not constitute
explicit permission to do anything.  Just the opposite:  they
give an explicit restriction NOT to do something.  Third the
interpretation you suggest is not consistent with all other
string library functions in the Standard:  they all don't do
anything past the final character explicitly processed, unless
there is some sort of explicit statement like "under such and
such circumstances the contents of the array is indeterminate."
There is no such explicit statement here.

By the way, the function I was talking about is wcstombs, not
mbstowcs.

> An application that provides an 'n' parameter larger than the
> allocated space of the destination buffer is _BROKEN_.

If you want to say it's not a good programming practice, I have
no problem with that.  But all the evidence I have found supports
the conclusion that the behavior gcc exhibits here does not
conform to what the Standard is meant to require.

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How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 13:30 +0200
  Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-11 13:55 +0200
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 14:01 +0200
      Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-11 09:08 -0400
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 15:19 +0200
        Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-11 18:32 +0200
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 18:59 +0200
          Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 17:42 +0000
            Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:30 +0200
            Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-12 00:29 -0400
              Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-12 14:41 +0200
              Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-12 16:19 +0200
  Re: How many wide characters may mbstowcs store? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-05-11 13:03 +0100
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 14:07 +0200
  Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 15:20 +0200
    Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 16:31 +0200
    Re: How many wide characters may mbstowcs store? Barry Schwarz <schwarzb@delq.com> - 2020-05-11 10:06 -0700
  Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 15:58 +0200
    Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-11 10:24 -0400
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 16:52 +0200
      Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-11 18:55 +0200
    Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 15:51 +0000
      Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 19:01 +0200
        Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 17:33 +0000
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:57 +0200
            Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 19:17 +0000
              Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 19:41 +0000
                Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 20:01 +0000
            Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 19:19 +0000
    Re: How many wide characters may mbstowcs store? Florian Weimer <fw@deneb.enyo.de> - 2020-05-11 20:24 +0200
      Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:59 +0200
        Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 19:17 +0000
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 21:24 +0200
        Re: How many wide characters may mbstowcs store? Florian Weimer <fw@deneb.enyo.de> - 2020-05-11 22:30 +0200
  Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 16:44 +0200
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 16:54 +0200
      Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 16:57 +0200
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 17:07 +0200
          Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 17:08 +0200
          Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-11 11:25 -0400
      Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-11 09:06 -0700
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 19:05 +0200
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 19:19 +0200
            Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-23 07:51 -0700
              Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-23 20:27 +0200
                Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-23 14:25 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-26 07:09 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-26 07:14 -0700
                Re: How many wide characters may mbstowcs store? Spiros Bousbouras <spibou@gmail.com> - 2020-05-26 16:00 +0000
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-29 21:23 -0700
                Re: How many wide characters may mbstowcs store? Spiros Bousbouras <spibou@gmail.com> - 2020-05-30 20:08 +0000
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-03 08:46 -0700
                Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-03 10:18 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-23 05:35 -0700
                Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-26 06:32 -0700
                Re: How many wide characters may mbstowcs store? raltbos@xs4all.nl (Richard Bos) - 2020-06-04 20:34 +0000
        Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 17:39 +0000
          Re: How many wide characters may mbstowcs store? Autist <autist69@gmail.com> - 2020-05-11 19:42 +0200
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:28 +0200
            Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 18:37 +0000
              Re: How many wide characters may mbstowcs store? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-05-11 11:50 -0700
                Re: How many wide characters may mbstowcs store? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-05-12 20:02 +0100
                Re: How many wide characters may mbstowcs store? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-05-12 13:12 -0700
          Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 19:56 +0000
          Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-24 16:49 -0700
      Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-11 14:19 -0700
        Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-11 14:22 -0700
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-12 09:17 +0200
        Re: How many wide characters may mbstowcs store? raltbos@xs4all.nl (Richard Bos) - 2020-05-24 16:12 +0000
          Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-24 15:10 -0700
          Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-24 22:58 -0400
  Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 20:07 +0000
  Re: How many wide characters may mbstowcs store? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2020-06-25 21:42 -0700
    Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-28 06:32 -0700

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