PHP上传文件

<?php   
 /*****************************************   
   Title :文件上传详解   
   Author:leehui1983(辉老大)   
   Finish Date  :2006-12-28   
  *****************************************/   
   $uploaddir = "./files/";//设置文件保存目录 注意包含/       
   $type=array("jpg","gif","bmp","jpeg","png");//设置允许上传文件的类型    
   $patch="http://127.0.0.1/cr_downloadphp/upload/files/";//程序所在路径   

   //获取文件后缀名函数   
      function fileext($filename)   
    {   
        return substr(strrchr($filename, '.'), 1);   
    }   
   //生成随机文件名函数       
    function random($length)   
    {   
        $hash = 'CR-';   
        $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz';   
        $max = strlen($chars) - 1;   
        mt_srand((double)microtime() * 1000000);   
            for($i = 0; $i < $length; $i++)   
            {   
                $hash .= $chars[mt_rand(0, $max)];   
            }   
        return $hash;   
    }   
   $a=strtolower(fileext($_FILES['file']['name']));   
   //判断文件类型   
   if(!in_array(strtolower(fileext($_FILES['file']['name'])),$type))   
     {   
        $text=implode(",",$type);   
        echo "您只能上传以下类型文件: ",$text,"<br>";   
     }   
   //生成目标文件的文件名       
   else{   
    $filename=explode(".",$_FILES['file']['name']);   
        do   
        {   
            $filename[0]=random(10); //设置随机数长度   
            $name=implode(".",$filename);   
            //$name1=$name.".Mcncc";   
            $uploadfile=$uploaddir.$name;   
        }   
   while(file_exists($uploadfile));   
        if (move_uploaded_file($_FILES['file']['tmp_name'],$uploadfile)){   

            if(is_uploaded_file($_FILES['file']['tmp_name'])){   
                //输出图片预览   
                echo "<center>您的文件已经上传完毕 上传图片预览: </center><br><center><img src='$uploadfile'></center>";   
                echo"<br><center><a href='javascript:history.go(-1)'>继续上传</a></center>";   
              }   
              else{   
                echo "上传失败！";   
              }   
        }   
   }    
?>