0) {        switch ($_FILES["img"]["error"]) {            case 1 :                echo "";                break;            case 2 :                echo "";                break;            case 3 :                echo "";                break;            case 4 :                echo "";                break;            default :                echo "";        }        exit;    }    $maxsize = 1000000000;    //step 2 使用$_FILES["pic"]["size"] 限制大小 单位字节 2M=2000000    if ($_FILES["img"]["size"] > $maxsize) {        echo "";        exit;    }    //step 3 使用$_FILES["pic"]["type"]或是文件的扩展名 限制类型 MIME image/gif image/png  gif png jpg    $allowtype = array("png", "gif", "jpg", "jpeg");    $arr = explode(".", $_FILES["img"]["name"]);    $hz = $arr[count($arr) - 1];    if (!in_array($hz, $allowtype)) {        echo "";        exit;    }    //step 4 将让传后的文件名改名    $filepath = "uploads/";    //为了符合UBB的路径    $randname = date("Y") . date("m") . date("d") . date("H") . date("i") . date("s") . rand(100, 999) . "." . $hz;    //将临时位置的文件移动到指定的目录上即可    if (is_uploaded_file($_FILES["img"]["tmp_name"])) {        if (move_uploaded_file($_FILES["img"]["tmp_name"], $filepath . $randname)) {            echo "";            session_start();            $_SESSION['images'] = $filepath . $randname;            //echo $_SESSION['images'];        } else {            echo "";        }    } else {        echo "";    }}?>