x                  The number of bytes stored in s, not including
                       the null terminating byte. If s is NULL,
                       wcstombs returns the number of bytes required
                       for the multibyte character array.
    (size_t) -1        Indicates an error occurred. The function sets
                       errno to EILSEQ - invalid character sequence,
                       or a wide-character code does not correspond
                       to a valid character.