Re: c32width gives incorrect return values in C locale

[Gavin Smith]

On Sat, Nov 11, 2023 at 11:54:52PM +0100, Bruno Haible wrote:
> [CCing bug-libunistring]
> Gavin Smith wrote:
> > I did not understand why uc_width was said to be "locale dependent":
> > 
> >   "These functions are locale dependent."
> > 
> > - from 
> > <https://www.gnu.org/software/libunistring/manual/html_node/uniwidth_002eh.html#index-uc_005fwidth>.
> 
> That's because some Unicode characters have "ambiguous width" — width 1 in
> Western locales, width 2 is East Asian locales (for historic and font choice
> reasons).
> 
> > I also don't understand the purpose of the "encoding" argument -- can this
> > always be "UTF-8"?
> 
> Yes, it can be always "UTF-8"; then uc_width will always choose width 1 for
> these characters.
> 
> > I'm also unclear on the exact relationship between the types char32_t,
> > ucs4_t and uint32_t.  For example, uc_width takes a ucs4_t argument
> > but u8_mbtouc writes to a char32_t variable.  In the code I committed,
> > I used a cast to ucs4_t when calling uc_width.
> 
> These types are all identical. Therefore you don't even need to cast.
> 
>   - char32_t comes from <uchar.h> (ISO C 11 or newer).
>   - ucs4_t comes from GNU libunistring.
>   - uint32_t comes from <stdint.h>.

Thanks for the advice.