MBRTOC16(3)

NAME
mbrtoc16 - Restartable multibyte to UTF-16 conversion

LIBRARY
libc

SYNOPSIS
#include <uchar.h>
size_t
mbrtoc16(char16_t * restrict pc16, const char * restrict s, size_t n, mbstate_t * restrict ps);

DESCRIPTION
The mbrtoc16 function decodes multibyte characters in the current locale and converts them to UTF-16, keeping state so it can restart after incremental progress.

Each call to mbrtoc16:
1.  examines up to n bytes starting at s,
2.  yields a UTF-16 code unit if available by storing it at *pc16,
3.  saves state at ps, and
4.  returns either the number of bytes consumed if any or a special return value.

Specifically:

•   If the multibyte sequence at s is invalid after any previous input saved at ps, or if an error occurs in decoding, mbrtoc16 returns (size_t)-1 and sets errno(2) to indicate the error.

•   If the multibyte sequence at s is still incomplete after n bytes, including any previous input saved in ps, mbrtoc16 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.

•   If mbrtoc16 had previously decoded a multibyte character but has not yet yielded all the code units of its UTF-16 encoding, it stores the next UTF-16 code unit at *pc16 and returns (size_t)-3. bytes of input are consumed in this case.

•   If mbrtoc16 decodes the null multibyte character, then it stores zero at *pc16 and returns zero.

•   Otherwise, mbrtoc16 decodes a single multibyte character, stores the first (and possibly only) code unit in its UTF-16 encoding at *pc16, and returns the number of bytes consumed to decode the first multibyte character.

If pc16 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 mbrtoc16 call is equivalent to:

mbrtoc16( NULL,, 1,ps)

This always returns zero, and has the effect of resetting ps to the initial conversion state, without writing to pc16, even if it is nonnull.

If ps is a null pointer, mbrtoc16 uses an internal mbstate_t object with static storage duration, distinct from all other mbstate_t objects ( including those used by mbrtoc8(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 mbrtoc16 function yields either a Unicode scalar value in the Basic Multilingual Plane (BMP), i.e., a 16-bit Unicode code point that is not a surrogate code point, or, over two successive calls, yields the high and low surrogate code points (in that order) of a Unicode scalar value outside the BMP.

RETURN VALUES
The mbrtoc16 function returns:

0   [null] if mbrtoc16 decoded a null multibyte character.

i   [code unit] where 1 i n, if mbrtoc16 consumed i bytes of input to decode the next multibyte character, yielding a UTF-16 code unit.

(size_t)-3
    [continuation] if mbrtoc16 consumed no new bytes of input but yielded a UTF-16 code unit that was pending from previous input.

(size_t)-2
    [incomplete] if mbrtoc16 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-16 code units of a multibyte string in hexadecimal text:

    char *s = ...;
    size_t n = ...;
    mbstate_t mbs = {0};    /* initial conversion state */
    while (n) {
            char16_t c16;
            size_t len;
            len = mbrtoc16(&c16, s, n, &mbs);
            switch (len) {
            case 0:         /* NUL terminator */
                    assert(c16 == 0);
                    goto out;
            default:        /* scalar value or high surrogate */
                    printf("U+%04"PRIx16"\n", (uint16_t)c16);
                    break;
            case (size_t)-3: /* low surrogate */
                    printf("continue U+%04"PRIx16"\n", (uint16_t)c16);
                    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
c16rtomb(3), c32rtomb(3), c8rtomb(3), mbrtoc32(3), mbrtoc8(3), uchar(3) The Unicode Standard, Version 15.0 — Core Specification, The Unicode Consortium, September 2022, https://www.unicode.org/versions/Unicode15.0.0/UnicodeStandard-15.0.pdf. P. Hoffman, F. Yergeau, UTF-16, an encoding of ISO 10646, RFC 2781, February 2000, Internet Engineering Task Force, https://datatracker.ietf.org/doc/html/rfc2781.

STANDARDS
The mbrtoc16 function conforms to isoC-2011.

HISTORY
The mbrtoc16 function first appeared in NetBSD 11.0.