# std::wcstombs

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< cpp‎ | string‎ | multibyte

Defined in header `<cstdlib>` |  |
std::size_t wcstombs( char* dst, const wchar_t* src, std::size_t len); |  |

Converts a sequence of wide characters from the array whose first element is pointed to by `src` to its narrow multibyte representation that begins in the initial shift state. Converted characters are stored in the successive elements of the char array pointed to by `dst`. No more than `len` bytes are written to the destination array.

Each character is converted as if by a call to std::wctomb, except that the wctomb's conversion state is unaffected. The conversion stops if:

- The null character was converted and stored.
- A wchar_t was found that does not correspond to a valid character in the current C locale.
- The next multibyte character to be stored would exceed `len`.

### Notes

In most implementations, this function updates a global static object of type std::mbstate_t as it processes through the string, and cannot be called simultaneously by two threads, std::wcsrtombs should be used in such cases.

POSIX specifies a common extension: if `dst` is a null pointer, this function returns the number of bytes that would be written to `dst`, if converted. Similar behavior is standard for std::wcsrtombs.

### Parameters

dst | - | pointer to narrow character array where the multibyte character will be stored
src | - | pointer to the first element of a null-terminated wide string to convert
len | - | number of byte available in the array pointed to by dst

### Return value

On success, returns the number of bytes (including any shift sequences, but excluding the terminating '\0') written to the character array whose first element is pointed to by `dst`.

On conversion error (if invalid wide character was encountered), returns static_cast<std::size_t>(-1).

### Example

Run this code

    #include <iostream>
    #include <clocale>
    #include <cstdlib>

    int main()
    {
        std::setlocale(LC_ALL, "en_US.utf8");
        // UTF-8 narrow multibyte encoding
        const wchar_t* wstr = L"z\u00df\u6c34\U0001d10b"; // or L"zß水𝄋"
        char mbstr[11];
        std::wcstombs(mbstr, wstr, 11);
        std::cout << "multibyte string: " << mbstr << '\n';
    }

Output:

    multibyte string: zß水𝄋

### See also

wcsrtombs | converts a wide string to narrow multibyte character string, given state (function)
mbstowcs | converts a narrow multibyte character string to wide string (function)
do_out [virtual] | converts a string from internT to externT, such as when writing to file (virtual protected member function of `std::codecvt`)
C documentation for wcstombs

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