The entries in $_FILES will be stored with the name of the tag from your
HTML form.Your form element is named userfile, so the array will have the following
contents:
n The value stored in $_FILES[‘userfile’][‘tmp_name’] is the place where the
file has been temporarily stored on the web server.
n The value stored in $_FILES[‘userfile’][‘name’] is the file’s name on the
user’s system.
n The value stored in $_FILES[‘userfile’][‘size’] is the size of the file in bytes.
n The value stored in $_FILES[‘userfile’][‘type’] is the MIME type of the
file―for example, text/plain or image/gif.
n The value stored in $_FILES[‘userfile’][‘error’] will give you any error
codes associated with the file upload.This functionality was added at PHP 4.2.0. ------解决方案-------------------- tmp_name，那是个随机的文件名
