Function iswalpha 

pub unsafe extern "C" fn iswalpha(__wc: wint_t) -> c_int

Test for any wide character for which iswupper' or 'iswlower' is true, or any wide character that is one of a locale-specific set of wide-characters for which none of iswcntrl’, iswdigit', iswpunct’, or `iswspace’ is true.