# std::wctomb

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< cpp‎ | string‎ | multibyte

Defined in header `<cstdlib>` |  |
int wctomb( char* s, wchar_t wc ); |  |

Converts a wide character wc to multibyte encoding and stores it (including any shift sequences) in the char array whose first element is pointed to by s. No more than MB_CUR_MAX characters are stored. The conversion is affected by the current locale's LC_CTYPE category.

If wc is the null character, the null byte is written to s, preceded by any shift sequences necessary to restore the initial shift state.

If s is a null pointer, resets the global conversion state and determines whether shift sequences are used.

### Parameters

s | - | pointer to the character array for output
wc | - | wide character to convert

### Return value

If s is not a null pointer, returns the number of bytes that are contained in the multibyte representation of wc or -1 if wc is not a valid character.

If s is a null pointer, resets its internal conversion state to represent the initial shift state and returns ​0​ if the current multibyte encoding is not state-dependent (does not use shift sequences) or a non-zero value if the current multibyte encoding is state-dependent (uses shift sequences).

### Notes

Each call to `wctomb` updates the internal global conversion state (a static object of type std::mbstate_t, only known to this function). If the multibyte encoding uses shift states, this function is not reentrant. In any case, multiple threads should not call `wctomb` without synchronization: std::wcrtomb may be used instead.

### Example

Run this code

    #include <clocale>
    #include <cstdlib>
    #include <iomanip>
    #include <iostream>
    #include <string>

    void print_wide(const std::wstring& wstr)
    {
        bool shifts = std::wctomb(nullptr, 0); // reset the conversion state
        std::cout << "shift sequences are " << (shifts ? "" : "not" )
                  << " used\n" << std::uppercase << std::setfill('0');
        for (const wchar_t wc : wstr)
        {
            std::string mb(MB_CUR_MAX, '\0');
            const int ret = std::wctomb(&mb[0], wc);
            const char* s = ret > 1 ? "s" : "";
            std::cout << "multibyte char '" << mb << "' is " << ret
                      << " byte" << s << ": [" << std::hex;
            for (int i{0}; i != ret; ++i)
            {
                const int c = 0xFF & mb[i];
                std::cout << (i ? " " : "") << std::setw(2) << c;
            }
            std::cout << "]\n" << std::dec;
        }
    }

    int main()
    {
        std::setlocale(LC_ALL, "en_US.utf8");
        // UTF-8 narrow multibyte encoding
        std::wstring wstr = L"z\u00df\u6c34\U0001d10b"; // or L"zß水𝄋"
        print_wide(wstr);
    }

Output:

    shift sequences are not used
    multibyte char 'z' is 1 byte: [7A]
    multibyte char 'ß' is 2 bytes: [C3 9F]
    multibyte char '水' is 3 bytes: [E6 B0 B4]
    multibyte char '𝄋' is 4 bytes: [F0 9D 84 8B]

### 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_out [virtual] | converts a string from `InternT` to `ExternT`, such as when writing to file (virtual protected member function of `std::codecvt<InternT,ExternT,StateT>`)

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