mbrtoc16

size_t mbrtoc16( char16_t* pc16, const char* s, size_t n, mbstate_t* ps );

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.

Parameters

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
• -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.
• -2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc16.
• -1 if encoding error occurs. Nothing is written to *pc16, the value EILSEQ is stored in errno and the value if *ps is unspecified.

Example

#include <stdio.h>
#include <locale.h>
#include <string.h>
#include <uchar.h>
 
mbstate_t state;
int main(void)
{
    setlocale(LC_ALL, "en_US.utf8");
    char *str = u8"z\u00df\u6c34\U0001F34C"; // or u8"zß水🍌"
 
    printf("Processing %zu UTF-8 bytes: [ ", strlen(str));
    for(char* p = str; *p; ++p) printf("%#x ", +(unsigned char)*p);
    puts("]");
 
    char16_t c16;
    char *ptr = str, *end = str + strlen(str)+1;
    int rc;
    while(rc = mbrtoc16(&c16, ptr, end - ptr, &state))
    {   
        printf("Next UTF-16 char: %#x obtained from ", c16);
        if(rc == -3)
            puts("earlier surrogate pair");
        else if(rc > 0) {
            printf("%d bytes [ ", rc);
            for(int n = 0; n < rc; ++n) printf("%#x ", +(unsigned char)ptr[n]);
            puts("]");
            ptr += rc;
        }
    }
}

Processing 10 UTF-8 bytes: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c ]
Next UTF-16 char: 0x7a obtained from 1 bytes [ 0x7a ]
Next UTF-16 char: 0xdf obtained from 2 bytes [ 0xc3 0x9f ]
Next UTF-16 char: 0x6c34 obtained from 3 bytes [ 0xe6 0xb0 0xb4 ]
Next UTF-16 char: 0xd83c obtained from 4 bytes [ 0xf0 0x9f 0x8d 0x8c ]
Next UTF-16 char: 0xdf4c obtained from earlier surrogate pair

References

• C11 standard (ISO/IEC 9899:2011):
• 7.28.1.1 The mbrtoc16 function (p: 398-399)

See also