MirOS Manual: optu16to8(3), wcrtomb(3)

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

NAME

     optu16to8, wcrtomb - converts a wide character to a multibyte character
     (restartable)

SYNOPSIS

     #include <wchar.h>

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

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

DESCRIPTION

     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, if ps is an initial conversion state.
     Contrary to and violating Version 3 of the Single UNIX Specification,
     this implementation can store more bytes in s if ps is not the initial
     conversion state. Starting with MirOS #10, MB_CUR_MAX has been adjusted
     to accomodate this fact, from the old value of "3" to a new value of "5"
     calculated by the formula "(old-MB_CUR_MAX * 2) - 1".

     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
                   page.

                   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.

RETURN VALUES

     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.

ERRORS

     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.

SEE ALSO

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

STANDARDS

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

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

HISTORY

     The optu16to8 function first appeared in MirOS #11.

AUTHORS

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

CAVEATS

     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 MirOS
     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 Unicode application is required to handle surrogates by it-
     self. 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.

MirOS BSD #10-current          February 9, 2014                              1

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This product includes material provided by Thorsten Glaser.

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