获得用户的真实IP地址

<?php

/**
* 获得用户的真实IP地址
*
* @return  string
*/
function real_ip(){
static $realip = NULL;

if ($realip !== NULL){
return $realip;
}

if (isset($_SERVER)){
if (isset($_SERVER['HTTP_X_FORWARDED_FOR'])){
$arr = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
/* 取X-Forwarded-For中第一个非unknown的有效IP字符串 */
foreach ($arr AS $ip){
$ip = trim($ip);

if ($ip != 'unknown'){
$realip = $ip;

break;
}
}
}
elseif (isset($_SERVER['HTTP_CLIENT_IP'])){
$realip = $_SERVER['HTTP_CLIENT_IP'];
}
else{
if (isset($_SERVER['REMOTE_ADDR'])){
$realip = $_SERVER['REMOTE_ADDR'];
}
else{
$realip = '0.0.0.0';
}
}
}
else{
if (getenv('HTTP_X_FORWARDED_FOR')){
$realip = getenv('HTTP_X_FORWARDED_FOR');
}
elseif (getenv('HTTP_CLIENT_IP')){
$realip = getenv('HTTP_CLIENT_IP');
}
else{
$realip = getenv('REMOTE_ADDR');
}
}

preg_match("/[\d\.]{7,15}/", $realip, $onlineip);
$realip = !empty($onlineip[0]) ? $onlineip[0] : '0.0.0.0';

return $realip;
}
?>