How many wide characters may mbstowcs store?

From	Philipp Klaus Krause <pkk@spth.de>
Newsgroups	comp.lang.c
Subject	How many wide characters may mbstowcs store?
Date	2020-05-11 13:30 +0200
Organization	solani.org
Message-ID	<r9bd16$nbt$1@solani.org> (permalink)

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In the current C draft (N2479) - wording hasn't changed since at least
C17 - it seems unclear how many wide characters mbstowcs may store:

"size_t mbstowcs(wchar_t * restrict pwcs, const char *restrict s, size_t n);

The mbstowcs function converts a sequence of multibyte characters that
begins in the initial shift state from the array pointed to by s into a
sequence of corresponding wide characters and stores not more than n
wide characters into the array pointed to by pwcs. No multibyte
characters that follow a null character (which is converted into a null
wide character) will be examined or converted. Each multibyte character
is converted as if by a call to the mbtowc function, except that the
conversion state of the mbtowc function is not affected.

No more than n elements will be modified in the array pointed to by
pwcs. If copying takes place between objects that overlap, the behavior
is undefined."

One could read that so that only converted characters are stored, so
nothing may be stored beyond a terminating 0. And indeed SDCC and my
Debian GNU/Linux system behave that way.

On the other hand, one could read that the only limit on the number of
characters stored is n. And indeed someone reported to me that on their
Ubuntu 18.04 LTS with gcc 7.5.0 both mbstowcs and wcstombs apparently
write beyond a terminating 0 (but do not exceed the limit n).

For wcstombs, the wording seems clear to state that it will stop at a
terminating 0, but for the mbstowcs it seems unclear to me.

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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? 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

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