随机字符串 php随机生成指定长度的字符串

function getCode($length=12) {

    //Ascii Code for number, lowercase, uppercase and special characters
    $no = range(48,57); 
    $lo = range(97,122);
    $up = range(65,90); 

    //exclude character I, l, 1, 0, O
    $eno = array(48, 49);
    $elo = array(108);
    $eup = array(73,79);
    $no = array_diff($no,$eno);
    $lo = array_diff($lo,$elo);
    $up = array_diff($up,$eup);
    $chr = array_merge($no, $lo, $up);

    for ($i=1;$i<=$length;$i++) {

        $code.= chr($chr[rand(0,count($chr)-1)]);   
    }
    return $code;
}