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Re: Is wchar_t really useful?

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On 11/13/2015 12:24 PM, Philipp Klaus Krause wrote:
> Could an implementation decide that characters in the execution
> character set are just the values of char? wchar_t could be 8 bits.
> The source character set could be utf-8 encoded unicode, and the
> characters in the execution character set would be the bytes of the
> utf-8 sequence.

UTF-8 is fine for the multibyte character encoding, but it doesn't work
for wchar_t:

"wchar_t
which is an integer type whose range of values can represent distinct
codes for all members of the largest extended character set specified
among the supported locales." (7.19p2)


> Would this violate "In a character constant or string literal, members
> of the execution character set shall be represented by corresponding
> members of the source character set […]" from 5.2.1?
> Unfortunately, that would mean that functions like mbrtoc32() couldn't
> convert to UTF-32 anymore, since they are supposed to read and interpret
> only one multibyte character at a time.

How did you reach that conclusion? mbrtoc32() reads multiple characters
through it's char* parameter:

"If s is not a null pointer, the mbrtoc32 function inspects at most n
bytes beginning with the byte pointed to by s to determine the number of
bytes needed to complete the next multibyte character (including any
shift sequences)."

I just noticed that I hadn't paid enough attention to the description of
mbrtoc32(). It can also convert a single multibyte input character into
multiple char32_t values - you just need to call mbrtoc32() multiple
times. It only stores one char32_t value at a time, but if the correct
translation results in multiple char32_t values, then "Subsequent calls
will store successive wide characters without consuming any additional
input until all the characters have been stored." mbrtoc16() has similar
wording - so that explains why UTF-16 and UTF-32 are permissible
encoding for char16_t and char32_t, respectively.

mbrtowc() does not have the wording about "Subsequent calls", which
confirms that UTF-like encodings are not permitted for wchar_t.

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Thread

Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-09 12:02 +0100
  Re: Is wchar_t really useful? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-09 03:24 -0800
    Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-10 18:33 -0600
      Re: Is wchar_t really useful? Ian Collins <ian-news@hotmail.com> - 2015-11-11 13:56 +1300
  Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-09 09:03 -0500
    Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-12 15:22 +0100
      Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-12 10:04 -0500
        Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-12 16:44 +0100
          Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-12 11:29 -0500
            Re: Is wchar_t really useful? supercat@casperkitty.com - 2015-11-12 09:14 -0800
              Re: Is wchar_t really useful? Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-14 11:50 -0800
                Re: Is wchar_t really useful? supercat@casperkitty.com - 2015-11-15 13:44 -0800
                Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-15 22:50 +0100
                Re: Is wchar_t really useful? supercat@casperkitty.com - 2015-11-15 14:46 -0800
                Re: Is wchar_t really useful? raltbos@xs4all.nl (Richard Bos) - 2015-11-17 22:34 +0000
                Re: Is wchar_t really useful? Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-16 07:25 -0800
            Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-13 17:26 +0100
              Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-13 13:36 -0500
                Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-13 16:37 -0600
                Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-13 17:58 -0500
              Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-13 16:01 -0600
                Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-13 23:36 +0100
    Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-12 15:28 +0100
      Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-12 10:26 -0500
    Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-12 14:27 -0600
  Re: Is wchar_t really useful? Lőrinczy Zsigmond <nospam@for.me> - 2015-11-13 05:02 +0100
    Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-13 11:52 +0100
      Re: Is wchar_t really useful? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-13 05:17 -0800
        Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-13 12:58 -0600
        Re: Is wchar_t really useful? supercat@casperkitty.com - 2015-11-13 11:14 -0800
    Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-13 12:45 -0600
  Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-13 18:24 +0100
    Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-13 13:55 -0500
      Re: Is wchar_t really useful? Philipp Klaus Krause <pkk@spth.de> - 2015-11-13 20:39 +0100
        Re: Is wchar_t really useful? James Kuyper <jameskuyper@verizon.net> - 2015-11-13 14:54 -0500
        Re: Is wchar_t really useful? Stephen Sprunk <stephen@sprunk.org> - 2015-11-13 17:04 -0600

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