php 获取访问者IP地址

static public function getip()
{
    if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown"))
    {
        $ip = getenv("HTTP_CLIENT_IP");
    }
    else if (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown"))
    {
        $ip = getenv("HTTP_X_FORWARDED_FOR");
    }
    else if (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknown"))
    {
        $ip = getenv("REMOTE_ADDR");
    }
    else if (isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], "unknown"))
    {
        $ip = $_SERVER['REMOTE_ADDR'];
    }
    else
    {
        $ip = "";
    }
    return($ip);
}
//该片段来自于http://outofmemory.cn