A complete PHP file upload class example explanation, _PHP tutorial

<&#63;php
define('NO_FILE', '不存在上传文件');
define('NOT_ALLOW_EXT', '文件类型不在允许范围内');
define('NOT_ALLOW_SIZE', '文件大小不在允许范围内');
define('HAS_THE_FILE', '该文件已经存在');
define('UPLOAD_FAILED', '上传失败');
define('UPLOAD_SUCCESS', '上传成功');
class file_uploader
{
  var $_file;
  var $_filesize;
  var $_fileext;
  var $_filedir;
  var $_filename;
  var $_filetmpname;
  
  var $allowsize;
  var $allowext;
  
  var $neednewname;
  var $newname;
  var $syslang;
  
  var $report;
  
  function ready($filedir = '', $file, $allowsize = '', $allowext = '', $neednewname = false, $report = 0){
    $this->_filedir = is_dir($filedir) &#63; $filedir : '';
    if(empty($file) || !isset($file['size']) || $file['size'] == 0) $this->error(NO_FILE);
    $this->_filesize = $file['size'];
    $this->_filename = $file['name'];
    $this->_filetmpname = $file['tmp_name'];
    
    $this->allowsize = $allowsize;
    $this->allowext = $allowext;
    
    $this->neednewname = ($neednewname) &#63; true : false;
    $this->newname = '';
    
    $this->report = $report;
  }
  
  function do_upload(){
    if(!is_uploaded_file($this->_filetmpname)) $this->error(NO_FILE);
    if($this->chk_ext()){
      $this->error(NOT_ALLOW_EXT);
      return '';
    }
    if($this->chk_size()){
      $this->error(NOT_ALLOW_SIZE);
      return '';
    }
    if($this->neednewname) $this->newname = $this->generate_name().".".$this->get_fileext();
    if($this->chk_hasfile()){
      $this->error(HAS_THE_FILE);
      return '';
    }
    $filename = empty($this->newname) &#63; @iconv('utf-8','gb2312',$this->_filename) : $this->newname;
    @chmod($this->_filedir.$filename, 0777);
    if(move_uploaded_file($this->_filetmpname, $this->_filedir.$filename)){
      return $this->result();
    }else{
      $this->error(UPLOAD_FAILED);
      return '';
    }
  }
  
  function chk_ext(){
    if(empty($this->allowext) || in_array($this->get_fileext(), explode("|",$this->allowext))) return false;
    return true;
  }
  
  function chk_size(){
    if(empty($this->allowsize) || get_filesize <= $this->allowsize*1024*1024) return false;
    return true;
  }
  
  function get_filesize(){
    return $this->_filesize;
  }
  
  function get_fileext(){
    return substr($this->_filename,strrpos($this->_filename,".")+1);
  }
  
  function generate_name(){
    return substr(md5(time()),26);
  }
  
  function chk_hasfile(){
    return is_file($this->_filedir.$this->_filename);
  }
  
  function error($tip){
    echo $tip;
  }
  
  function result(){
    if($this->report){
      $filename = empty($this->newname) &#63; $this->_filename : $this->newname;
      $arr = array('filename' => $filename, 'filesize' => $this->_filesize, 'tip' => UPLOAD_SUCCESS);
      return $arr;
    }else{
      return UPLOAD_SUCCESS;
    }
  }
}
/***使用方法与参数说明***/
/***
  第一个参数$dir 为上传文件存放的路径
   第二个参数为$_FILES 为你那个上传文件变量
   第三个参数允许文件大小 单位为MB
  第四个参数允许的文件类型 格式为jpg|png|gif
  第五个参数是否需要生成新的文件名
   第六个参数为返回的提示格式 0为直接提示上传正确 1则返回一个数组array('filename' => $filename, 'filesize' => $this->_filesize, 'tip' => UPLOAD_SUCCESS);
***/
//require("类文件");
//$u = new file_uploader;
//$u->ready($dir, $_FILES['upload_file'], false, false, true, 0);
//echo $u->do_upload();
&#63;>

$dir = 'upload/';
  require("upload_class.php");
  $u = new file_uploader;
  $u->ready($dir, $_FILES['upload_file'], false, false, true, 0);
  echo $u->do_upload();