MirBSD manpage: optu16to8(3), wcrtomb(3)

WCRTOMB(3)                 BSD Programmer's Manual                  WCRTOMB(3)


     optu16to8, wcrtomb - converts a wide character to a multibyte character


     #include <wchar.h>

     optu16to8(char *s, wchar_t wc, mbstate_t *ps);

     wcrtomb(char *s, wchar_t wc, mbstate_t *ps);


     wcrtomb() converts the wide character given by wc to the corresponding
     multibyte character, and stores it in the array pointed to by s unless s
     is a null pointer. This function will modify the first at most MB_CUR_MAX
     bytes of the array pointed by s.

     The behaviour of wcrtomb() is affected by the LC_CTYPE category of the
     current locale.

     optu16to8() behaves similar to wcrtomb(), but always converts from
     OPTU-16 to OPTU-8 encoding, independent of the current locale.

     These are the special cases:

     wc == 0       For state-dependent encodings, wcrtomb() stores a null byte
                   preceded by a special byte sequence (if any) to return to
                   an initial state to the array pointed by s, and the state
                   object pointed by ps also returned to a initial state.

     s == NULL     wcrtomb() just places ps into a initial state. It is
                   equivalent to the following call:

                         wcrtomb(buf, L'\0', ps);

                   Here, buf is a dummy buffer. In this case, wc is ignored.

     ps == NULL    mbrtowc() uses its own internal state object to keep the
                   conversion state, instead of ps mentioned in this manual

                   Calling any other functions in libc never changes the
                   internal states of optu16to8() or mbrtowc(), which are ini-
                   tialised at startup time of the program.


     optu16to8() and wcrtomb() return:

     positive      The number of bytes (including any shift sequences) which
                   are stored in the array.

     (size_t)-1    wc is not a valid wide character. In this case, wcrtomb()
                   also sets errno to indicate error.


     optu16to8() and wcrtomb() may cause an error in the following cases:

     [EILSEQ]      wc is not a valid wide character.

     [EINVAL]      ps points to an invalid or uninitialised mbstate_t object.


     iswoctet(3), optu8to16(3), setlocale(3), wctomb(3)


     The wcrtomb() function conforms to ISO/IEC 9899/AMD1:1995 ("ISO C90,
     Amendment 1").

     At present, MirBSD is limited to the UCS BMP (Basic Multilingual Plane),
     thus OPTU-8 is limited to the common subset of CESU-8 and UTF-8.


     The optu16to8 function first appeared in MirBSD #11.


     Thorsten Glaser <tg@mirbsd.de> wrote the entire internationalisation im-
     plementation in MirBSD. He is also the steward for the OPTU encoding.


     On a system whose wide character type is only 16 bits wide, as opposed to
     31 bits of ISO 10646, the OPTU encoder and decoder are permitted to not
     de- and recompose any surrogates encountered and pass them through as if
     they were regular wide characters with no special function. Since MirBSD
     is such a system, the reference implementation does not care about UTF-16
     surrogates (U+D800 to U+DFFF) posing as OPTU-16 characters at all; a
     planes-aware Universal Coded Character Set-using application is required
     to handle surrogates by itself. For compatibility purposes, optu16to8
     should always be assumed to not treat surrogates specially; applications
     must ensure to not produce invalid surrogates unless limited to the BMP.

     optu16to8() does, however, correctly reject the codepoints U+FFFE and
     U+FFFF as invalid.

MirBSD #10-current               July 7, 2021                                1

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