mbrtowc

Converts a narrow multibyte character to its wide character representation.

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, and taking into account the current multibyte conversion state *ps). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding wide character and stores it in *pwc (if pwc is not null).

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

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

If the environment macro __STDC_ISO_10646__ is defined, the values of type wchar_t are the same as the short identifiers of the characters in the Unicode required set (typically UTF-32 encoding); 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 pwc if non-null) was the null character
• the number of bytes [1...n] of the multibyte character successfully converted from s
• (size_t)-2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pwc.
• (size_t)-1 if encoding error occurs. Nothing is written to *pwc, the value EILSEQ is stored in errno and the value of *ps is left unspecified.

Example

#include <stdio.h>
#include <locale.h>
#include <string.h>
#include <wchar.h>
 
int main(void)
{
    setlocale(LC_ALL, "en_US.utf8");
    mbstate_t state;
    memset(&state, 0, sizeof state);
    char in[] = u8"z\u00df\u6c34\U0001F34C"; // or u8"zß水🍌"
    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("]");
 
    wchar_t out[in_sz];
    char *p_in = in, *end = in + in_sz;
    wchar_t *p_out = out;
    int rc;
    while((rc = mbrtowc(p_out, p_in, end - p_in, &state)) > 0)
    {
        p_in += rc;
        p_out += 1;
    }
 
    size_t out_sz = p_out - out + 1;
    printf("into %zu wchar_t units: [ ", out_sz);
    for(size_t x = 0; x < out_sz; ++x) printf("%#x ", out[x]);
    puts("]");
}

Processing 11 UTF-8 code units: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c 0 ]
into 5 wchar_t units: [ 0x7a 0xdf 0x6c34 0x1f34c 0 ]

References