Re: From wchar_t to char32_t

[Paul Eggert]

On 7/2/23 13:18, Bruno Haible wrote:
> Paul Eggert wrote:
> > When can we get (size_t) -3 in a real-world system?
>
> It can/could occur if all of the following conditions are met:
>
>    * The locale encoding is BIG5-HKSCS, e.g. on a glibc system the
>      zh_HK.BIG5-HKSCS the locale.
>
>    * The input is one of the 4 characters in that encoding that map to
>      a sequence of two Unicode characters:
>
>         input         maps to
>         -----         -------
>       0x88 0x62    U+00CA U+0304
>       0x88 0x64    U+00CA U+030C
>       0x88 0xA3    U+00EA U+0304
>       0x88 0xA5    U+00EA U+030C >       ...

I looked into this some more and unfortunately don't understand the 
above. Could you explain a bit more?

<http://www.nits.org.cn/index/article/4034> says that the official 
mapping table for GB 18030-2022 and BMP is here:

http://www.nits.org.cn/cmsfile/download/134

and this contains the following (nonconsecutive) lines:

  5746  8862
  5749  8864
  57BC  88A3
  57BE  88A5

which, if I understand things correctly, means the four two-byte 
sequences that you mention should convert to the following four Unicode 
characters:

  坆 U+5746 CJK IDEOGRAPH-5746
  坉 U+5749 CJK IDEOGRAPH-5749
  垼 U+57BC CJK IDEOGRAPH-57BC
  垾 U+57BE CJK IDEOGRAPH-57BE

without mbrtoc23 having to return (size_t) -3.

Perhaps there was a problem with an earlier version of GB 18030 that has 
been fixed in the 2022 edition?