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MBRTOC8(3) FreeBSD Library Functions Manual MBRTOC8(3) NAME mbrtoc8 - Restartable multibyte to UTF-8 conversion LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <uchar.h> size_t mbrtoc8(char8_t * restrict pc8, const char * restrict s, size_t n, mbstate_t * restrict ps); DESCRIPTION The mbrtoc8 function decodes multibyte characters in the current locale and converts them to UTF-8, keeping state so it can restart after incremental progress. Each call to mbrtoc8: 1. examines up to n bytes starting at s, 2. yields a UTF-8 code unit if available by storing it at *pc8, 3. saves state at ps, and 4. returns either the number of bytes consumed if any or a special return value. Specifically: o If the multibyte sequence at s is invalid after any previous input saved at ps, or if an error occurs in decoding, mbrtoc8 returns (size_t)-1 and sets errno(2) to indicate the error. o If the multibyte sequence at s is still incomplete after n bytes, including any previous input saved in ps, mbrtoc8 saves its state in ps after all the input so far and returns (size_t)-2. All n bytes of input are consumed in this case. o If mbrtoc8 had previously decoded a multibyte character but has not yet yielded all the code units of its UTF-8 encoding, it stores the next UTF-8 code unit at *pc8 and returns (size_t)-3. No input is consumed in this case. o If mbrtoc8 decodes the null multibyte character, then it stores zero at *pc8 and returns zero. o Otherwise, mbrtoc8 decodes a single multibyte character, stores the first (and possibly only) code unit in its UTF-8 encoding at *pc8, and returns the number of bytes consumed to decode the first multibyte character. If pc8 is a null pointer, nothing is stored, but the effects on ps and the return value are unchanged. If s is a null pointer, the mbrtoc8 call is equivalent to: mbrtoc8(NULL, "", 1, ps) This always returns zero, and has the effect of resetting ps to the initial conversion state, without writing to pc8, even if it is nonnull. If ps is a null pointer, mbrtoc8 uses an internal mbstate_t object with static storage duration, distinct from all other mbstate_t objects (including those used by mbrtoc16(3), mbrtoc32(3), c8rtomb(3), c16rtomb(3), and c32rtomb(3)), which is initialized at program startup to the initial conversion state. IMPLEMENTATION NOTES On well-formed input, the mbrtoc8 function yields either a Unicode scalar value in US-ASCII range, i.e., a 7-bit Unicode code point, or, over two to four successive calls, the leading and trailing code units in order of the UTF-8 encoding of a Unicode scalar value outside the US-ASCII range. RETURN VALUES The mbrtoc8 function returns: 0 [null] if mbrtoc8 decoded a null multibyte character. i [code unit] where 1 <= i <= n, if mbrtoc8 consumed i bytes of input to decode the next multibyte character, yielding a UTF-8 code unit. (size_t)-3 [continuation] if mbrtoc8 consumed no new bytes of input but yielded a UTF-8 code unit that was pending from previous input. (size_t)-2 [incomplete] if mbrtoc8 found only an incomplete multibyte sequence after all n bytes of input and any previous input, and saved its state to restart in the next call with ps. (size_t)-1 [error] if any encoding error was detected; errno(2) is set to reflect the error. EXAMPLES Print the UTF-8 code units of a multibyte string in hexadecimal text: char *s = ...; size_t n = ...; mbstate_t mbs = {0}; /* initial conversion state */ while (n) { char8_t c8; size_t len; len = mbrtoc8(&c8, s, n, &mbs); switch (len) { case 0: /* NUL terminator */ assert(c8 == 0); goto out; default: /* consumed input and yielded a byte c8 */ printf("0x%02hhx\n", c8); break; case (size_t)-3: /* yielded a pending byte c8 */ printf("continue 0x%02hhx\n", c8); break; case (size_t)-2: /* incomplete */ printf("incomplete\n"); goto readmore; case (size_t)-1: /* error */ printf("error: %d\n", errno); goto out; } s += len; n -= len; } ERRORS [EILSEQ] The multibyte sequence cannot be decoded in the current locale as a Unicode scalar value. [EIO] An error occurred in loading the locale's character conversions. SEE ALSO c8rtomb(3), c16rtomb(3), c32rtomb(3), mbrtoc16(3), mbrtoc32(3), uchar(3) The Unicode Standard, https://www.unicode.org/versions/Unicode15.0.0/UnicodeStandard-15.0.pdf, The Unicode Consortium, September 2022, Version 15.0 -- Core Specification. F. Yergeau, UTF-8, a transformation format of ISO 10646, Internet Engineering Task Force, RFC 3629, https://datatracker.ietf.org/doc/html/rfc3629, November 2003. HISTORY The mbrtoc8 function first appeared in NetBSD 11.0. FreeBSD 14.1-RELEASE-p8 August 15, 2024 FreeBSD 14.1-RELEASE-p8