# std::mbrtowc

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< cpp‎ | string‎ | multibyte

Defined in header `<cwchar>` |  |
std::size_t mbrtowc( wchar_t* pwc, const char* s, std::size_t n, std::mbstate_t* ps ); |  |

Converts a narrow multibyte character to a wide character.

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 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 std::mbrtowc(NULL, "", 1, ps).

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

### 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 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`
- static_cast<std::size_t>(-2) if the next `n` bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pwc.
- static_cast<std::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 <iostream>
    #include <clocale>
    #include <cstring>
    #include <cwchar>

    void print_mb(const char* ptr)
    {
        std::mbstate_t state = std::mbstate_t(); // initial state
        const char* end = ptr + std::strlen(ptr);
        int len;
        wchar_t wc;
        while((len = std::mbrtowc(&wc, ptr, end-ptr, &state)) > 0) {
            std::wcout << "Next " << len << " bytes are the character " << wc << '\n';
            ptr += len;
        }
    }

    int main()
    {
        std::setlocale(LC_ALL, "en_US.utf8");
        // UTF-8 narrow multibyte encoding
        const char* str = u8"z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋"
                          // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";
        print_mb(str);
    }

Output:

    Next 1 bytes are the character z
    Next 2 bytes are the character ß
    Next 3 bytes are the character 水
    Next 4 bytes are the character 𝄋

### See also

mbtowc | converts the next multibyte character to wide character (function)
wcrtomb | converts a wide character to its multibyte representation, given state (function)
do_in [virtual] | converts a string from externT to internT, such as when reading from file (virtual protected member function of `std::codecvt<InternT,ExternT,State>`)

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