The wctomb function converts the wide character specified by
    wchar to its multibyte character representation. If s is NULL,
    then 0 is returned. Otherwise, the number of bytes comprising the
    multibyte character is returned. At most, MB_CUR_MAX bytes are
    stored in the array object pointed to by s.

    This function is affected by the LC_CTYPE category of the
    program's current locale.