获得客户端IP

<?php 
function GetIP() { //获取IP     
    if ($_SERVER["HTTP_X_FORWARDED_FOR"])     
        $ip = $_SERVER["HTTP_X_FORWARDED_FOR"];     
    else if ($_SERVER["HTTP_CLIENT_IP"])     
        $ip = $_SERVER["HTTP_CLIENT_IP"];     
    else if ($_SERVER["REMOTE_ADDR"])     
        $ip = $_SERVER["REMOTE_ADDR"];  
    else if (getenv("HTTP_X_FORWARDED_FOR"))     
        $ip = getenv("HTTP_X_FORWARDED_FOR");     
    else if (getenv("HTTP_CLIENT_IP"))     
        $ip = getenv("HTTP_CLIENT_IP");     
    else if (getenv("REMOTE_ADDR"))     
        $ip = getenv("REMOTE_ADDR");     
    else     
        $ip = "Unknown";     
    return $ip;     
}     
?>