WCRTOMB(3) BSD Programmer's Manual WCRTOMB(3)
wcrtomb - converts a wide character to a multibyte character (restart-
able)
#include <wchar.h>
size_t
wcrtomb(char * restrict s, wchar_t wc, mbstate_t * restrict 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.
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 state of wcrtomb(), which is initialised at start-
up time of the program.
wcrtomb() returns:
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.
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.
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, wcrtomb
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 December 11, 2021 1