php判断访问IP的方法

<?php 
function getIP() { 
  if (! empty ( $_SERVER ["HTTP_CLIENT_IP"] )) { 
    $cip = $_SERVER ["HTTP_CLIENT_IP"]; 
  } else if (! empty ( $_SERVER ["HTTP_X_FORWARDED_FOR"] )) { 
    $cip = $_SERVER ["HTTP_X_FORWARDED_FOR"]; 
  } else if (! empty ( $_SERVER ["REMOTE_ADDR"] )) { 
    $cip = $_SERVER ["REMOTE_ADDR"]; 
  } else { 
    $cip = ''; 
  } 
  preg_match ( "/[\d\.]{7,15}/", $cip, $cips ); 
  $cip = isset ( $cips [0] ) ? $cips [0] : 'unknown'; 
  unset ( $cips ); 
  return $cip; 
} 
?>