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# mbrtoc16

From cppreference.com
< c‎ | string‎ | multibyte

Defined in header `<uchar.h>` |  |
size_t mbrtoc16( char16_t* pc16, const char* s, size_t n, mbstate_t* ps ); |  | (since C11)

Converts a single code point from its narrow multibyte character representation to its variable-length 16-bit wide character representation (typically, UTF-16).

If `s` is not a null pointer, inspects at most `n` bytes of the multibyte character string, beginning with the byte pointed to by `s` to determine the number of bytes necessary to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character in `s` is complete and valid, converts it to the corresponding 16-bit wide character and stores it in *pc16 (if `pc16` is not null).

If the multibyte character in `*s` corresponds to a multi-char16_t sequence (e.g. a surrogate pair in UTF-16), then after the first call to this function, `*ps` is updated in such a way that the next call to `mbrtoc16` will write out the additional char16_t, without considering `*s`.

If `s` is a null pointer, the values of `n` and `pc16` are ignored and the call is equivalent to mbrtoc16(NULL, "", 1, ps).

If the wide character produced is the null character, the conversion state *ps represents the initial shift state.

If the macro __STDC_UTF_16__ is defined, the 16-bit encoding used by this function is UTF-16; otherwise, it is implementation-defined. In any case, the multibyte character encoding used by this function is specified by the currently active C locale.

### [edit] Parameters

pc16 | - | pointer to the location where the resulting 16-bit wide character will be written
s | - | pointer to the multibyte character string used as input
n | - | limit on the number of bytes in s that can be examined
ps | - | pointer to the conversion state object used when interpreting the multibyte string

### [edit] Return value

The first of the following that applies:

- ​0​ if the character converted from `s` (and stored in *pc16 if non-null) was the null character
- the number of bytes [1...n] of the multibyte character successfully converted from `s`
- (size_t)-3 if the next char16_t from a multi-char16_t character (e.g. a surrogate pair) has now been written to *pc16. No bytes are processed from the input in this case.
- (size_t)-2 if the next `n` bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc16.
- (size_t)-1 if encoding error occurs. Nothing is written to `*pc16`, the value EILSEQ is stored in errno and the value if *ps is unspecified.

### [edit] Example

Run this code

    #include <stdio.h>
    #include <locale.h>
    #include <uchar.h>

    mbstate_t state;
    int main(void)
    {
        setlocale(LC_ALL, "en_US.utf8");
        char in[] = u8"zß水🍌"; // or "z\u00df\u6c34\U0001F34C"
        size_t in_sz = sizeof in / sizeof *in;

        printf("Processing %zu UTF-8 code units: [ ", in_sz);
        for(size_t n = 0; n < in_sz; ++n) printf("%#x ", (unsigned char)in[n]);
        puts("]");

        char16_t out[in_sz];
        char *p_in = in, *end = in + in_sz;
        char16_t *p_out = out;
        int rc;
        while((rc = mbrtoc16(p_out, p_in, end - p_in, &state)))
        {
            if(rc == -3) // surrogate pairs in UTF-16
                p_out += 1;
            else if(rc > 0) {
                p_in += rc;
                p_out += 1;
            } else break;
        }

        size_t out_sz = p_out - out + 1;
        printf("into %zu UTF-16 code units: [ ", out_sz);
        for(size_t x = 0; x < out_sz; ++x) printf("%#x ", out[x]);
        puts("]");
    }

Output:

    Processing 11 UTF-8 code units: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c 0 ]
    into 6 UTF-16 code units: [ 0x7a 0xdf 0x6c34 0xd83c 0xdf4c 0 ]

### [edit] References

- C11 standard (ISO/IEC 9899:2011):

  - 7.28.1.1 The mbrtoc16 function (p: 398-399)

### [edit] See also

c16rtomb (C11) | converts a 16-bit wide character to narrow multibyte string (function) [edit]
C++ documentation for mbrtoc16

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