<?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;