PHP另类方法 生成随机字符串

function getRandStr($n=6){
    $str = "";
    for( $i=0; $i<$n; $i++ ){
        $case = rand(0, 2);
        switch($case){
            case 0:
                /* ASCII 97-122 a-z */
                $str .= chr(rand(97, 122)) ;
                break;
            case 1:
                /* ASCII 65-90 A-Z */
                $str .= chr(rand(65, 90)) ;
                break;
            case 2:
                /* ASCII 48-57 0-9 */
                $str .= chr(rand(48, 57)) ;
                break;
        }
    }
    return $str;
}

echo getRandStr(32);