PHP code to record visitor IP address

 //File name
 $filename = "ip.txt";
 if (isset($_SERVER['HTTP_CLIENT_IP']))
 {
 $clientip = $_SERVER['HTTP_CLIENT_IP' ];
 }elseif (isset($_SERVER['HTTP_X_FORWARD_FOR']))
 {
 $clientip = $_SERVER['HTTP_X_FORWARD_FOR'];
 }else
 {
 $clientip = $_SERVER['REMOTE_ADDR'];
 }
 //Open the file (the file does not exist and will be created automatically)
 if (!$fp = fopen($filename, "a+"))
 {
 echo "Cannot open file$";
 exit;
 }
 //Write It also determines whether there is duplicate data
 while(!feof($fp))
 {
 $line = fgets($fp);
 if($line == ($clientip."n"))
 {
 exit; //Exit if there is duplicate data;
 }
 }
 //Write to file
 if(!fwrite($fp,$clientip."n"))
 {
 echo "Cannot write to file $filename" ;
 exit;
 }
 //Writing to file has been completed
 fclose($fp);
 ?>