怎么样使用PHP获取用户访问IP地址？

<?php                                 //方法1：
$ip = $_SERVER["REMOTE_ADDR"];
echo $ip;
 
//方法2：
$user_IP = ($_SERVER["HTTP_VIA"]) ? $_SERVER["HTTP_X_FORWARDED_FOR"] : $_SERVER["REMOTE_ADDR"];
$user_IP = ($user_IP) ? $user_IP : $_SERVER["REMOTE_ADDR"];
echo $user_IP;
 
//方法3：
function getRealIp()
{
 $ip=false;
 if(!empty($_SERVER["HTTP_CLIENT_IP"])){
  $ip = $_SERVER["HTTP_CLIENT_IP"];
 }
 if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
  $ips = explode (", ", $_SERVER['HTTP_X_FORWARDED_FOR']);
  if ($ip) { array_unshift($ips, $ip); $ip = FALSE; }
  for ($i = 0; $i < count($ips); $i++) {
   if (!eregi ("^(10│172.16│192.168).", $ips[$i])) {
    $ip = $ips[$i];
    break;
   }
  }
 }
 return ($ip ? $ip : $_SERVER['REMOTE_ADDR']);
}
echo getRealIp();
 
//方法4：
if ($HTTP_SERVER_VARS["HTTP_X_FORWARDED_FOR"])
{
 $ip = $HTTP_SERVER_VARS["HTTP_X_FORWARDED_FOR"];
}
elseif ($HTTP_SERVER_VARS["HTTP_CLIENT_IP"])
{
 $ip = $HTTP_SERVER_VARS["HTTP_CLIENT_IP"];
}
elseif ($HTTP_SERVER_VARS["REMOTE_ADDR"])
{
 $ip = $HTTP_SERVER_VARS["REMOTE_ADDR"];
}
elseif (getenv("HTTP_X_FORWARDED_FOR"))
{
 $ip = getenv("HTTP_X_FORWARDED_FOR");
}
elseif (getenv("HTTP_CLIENT_IP"))
{
 $ip = getenv("HTTP_CLIENT_IP");
}
elseif (getenv("REMOTE_ADDR"))
{
 $ip = getenv("REMOTE_ADDR");
}
else
{
 $ip = "Unknown";
}
echo $ip ;
 
//方法5：
if(getenv('HTTP_CLIENT_IP')) {
 $onlineip = getenv('HTTP_CLIENT_IP');
} elseif(getenv('HTTP_X_FORWARDED_FOR')) {
 $onlineip = getenv('HTTP_X_FORWARDED_FOR');
} elseif(getenv('REMOTE_ADDR')) {
 $onlineip = getenv('REMOTE_ADDR');
} else {
 $onlineip = $HTTP_SERVER_VARS['REMOTE_ADDR'];
}
echo $onlineip;