# mbrtowc

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< c‎ | string‎ | multibyte

Defined in header `<wchar.h>` |  |
size_t mbrtowc( wchar_t* pwc, const char* s, size_t n, mbstate_t* ps ); |  | (since C95)
size_t mbrtowc( wchar_t *restrict pwc, const char *restrict s, size_t n, mbstate_t *restrict ps ); |  | (since C99)

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

pwc | - | pointer to the location where the resulting 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 used when interpreting the multibyte character string

### 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

Run this code

    #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("]");
    }

Output:

    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

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

  - 7.29.6.3.2 The mbrtowc function (p: 443)

- C99 standard (ISO/IEC 9899:1999):

  - 7.24.6.3.2 The mbrtowc function (p: 389)

### See also

mbtowc | converts the next multibyte character to wide character (function)
wcrtomb wcrtomb_s (C95)(C11) | converts a wide character to its multibyte representation, given state (function)

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