MBRTOC32(3) | Library Functions Manual | MBRTOC32(3)

# NAME

`mbrtoc32` —
Restartable multibyte to UTF-32 conversion

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

`#include <uchar.h>`

size_t
`mbrtoc32`(char32_t * restrict pc32, const char * restrict s, size_t n, mbstate_t * restrict ps);

# DESCRIPTION

The `mbrtoc32` function decodes multibyte characters in the current locale and converts them to Unicode scalar values (i.e., to UTF-32), keeping state so it can restart after incremental progress.

Each call to `mbrtoc32`:

1. examines up to n bytes starting at s,
2. yields a Unicode scalar value (i.e., a UTF-32 code unit) if available by storing it at `*`pc32,
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, `mbrtoc32` 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, `mbrtoc32` saves its state in ps after all the input so far and returns `(size_t)-2`.
- If `mbrtoc32` decodes the null multibyte character, then it stores zero at `*`pc32 and returns zero.
- Otherwise, `mbrtoc32` decodes a single multibyte character, stores its Unicode scalar value at `*`pc32, and returns the number of bytes consumed to decode the first multibyte character.

If pc32 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 `mbrtoc32` call is equivalent to:

`mbrtoc32`(`NULL`, `""`, `1`, ps);

This always returns zero, and has the effect of resetting ps to the initial conversion state, without writing to pc32, even if it is nonnull.

If ps is a null pointer, `mbrtoc32` uses an internal mbstate_t object with static storage duration, distinct from all other mbstate_t objects (including those used by mbrtoc8(3), mbrtoc16(3), c8rtomb(3), c16rtomb(3), and c32rtomb(3)), which is initialized at program startup to the initial conversion state.

# RETURN VALUES

The `mbrtoc32` function returns:

`0`
  [null] if `mbrtoc32` decoded a null multibyte character.
i
  [scalar value] where `0` ≤ i ≤ n, if `mbrtoc32` consumed i bytes of input to decode the next multibyte character, yielding a Unicode scalar value.
`(size_t)-2`
  [incomplete] if `mbrtoc32` 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

    char *s = ...;
    size_t n = ...;
    mbstate_t mbs = {0};    /* initial conversion state */

    while (n) {
            char32_t c32;
            size_t len;

            len = mbrtoc32(&c32, s, n, &mbs);
            switch (len) {
            case 0:                 /* NUL terminator */
                    assert(c32 == 0);
                    goto out;
            default:                /* scalar value */
                    printf("U+%04"PRIx32"\n", (uint32_t)c32);
                    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), mbrtoc16(3), mbrtoc8(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.

# STANDARDS

The `mbrtoc32` function conforms to ISO/IEC 9899:2011 (“ISO C11”).

# HISTORY

The `mbrtoc32` function first appeared in NetBSD 11.0.

August 14, 2024 | NetBSD 10.1