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; 
} 
?>