php记录访问者IP地址的代码

 //文件名字
 $filename = "ip.txt";
  if (isset($_SERVER['HTTP_CLIENT_IP']))
  {
  $clientip = $_SERVER['HTTP_CLIENT_IP'];
  }elseif (isset($_SERVER['HTTP_X_FORWARD_FOR']))
  {
  $clientip = $_SERVER['HTTP_X_FORWARD_FOR'];
  }else
  {
  $clientip = $_SERVER['REMOTE_ADDR'];
  }
  //打开文件（文件不存在自动建立）
  if (!$fp = fopen($filename, "a+"))
  {
   echo "不能打开文件$";
  exit;
  }
 //写入的时候还判断是否已经有重复数据
 while(!feof($fp))
 {
  $line = fgets($fp);
  if($line == ($clientip."\n"))
  {
   exit;  //有重复数据就退出；
  }
 }
 // 写入文件
  if(!fwrite($fp,$clientip."\n"))
  {
   echo "不能写入到文件$filename" ;
  exit;
  }
  //已经完成写入文件
  fclose($fp);
 ?>