Re: should mbrtowc(&wc, "", 1, &ps) set wc?

[Markus Kuhn <Markus dot Kuhn at cl dot cam dot ac dot uk>]

Edmund GRIMLEY EVANS wrote on 2000-11-11 16:56 UTC:
> Should mbrtowc(&wc, "", 1, &ps) set wc?

Yes. It must set wc=0 and return 0 (at least in all ISO 8859 and UTF-8
locales), because the next 1 byte is (and therefore completes) "the
multibyte character that corresponds to the null wide  character".

ISO/IEC 9899:1999:

       7.24.6.3.2  The mbrtowc function

       [...]

       [#4] The mbrtowc function returns the first of the following
       that applies (given the current conversion state):

       0               if the next n or fewer  bytes  complete  the
                       multibyte  character that corresponds to the
                       null wide  character  (which  is  the  value
                                              ^^^^^^^^^^^^^^^^^^^^^
                       stored).
                       ^^^^^^

       [...]

> Apparently it does with glibc-2.1 and with Bruno's libutf8, but it
> doesn't with glibc-2.2 (from CVS a few days ago).

That sounds indeed like a glibc 2.2 bug then.

> Program:
> 
> #include <locale.h>
> #include <stdio.h>
> #include <wchar.h>
> 
> int main()
> {
>   mbstate_t ps;
>   size_t r;
>   wchar_t wc = 333;
> 
>   setlocale(LC_ALL, "");
> 
>   memset(&ps, 0, sizeof(ps));
>   r = mbrtowc(&wc, "a", 1, &ps);
>   printf("%d %d\n", r, (int)wc);
>   r = mbrtowc(&wc, "", 1, &ps);
>   printf("%d %d\n", r, (int)wc);
> 
>   return 0;
> }
> 
> Result with glibc-2.1 or libutf8:
> 
> 1 97
> 0 0
> 
> Result with glibc-2.2:
> 
> 1 97
> 0 97

Markus

-- 
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org,  WWW: <http://www.cl.cam.ac.uk/~mgk25/>