取得IP地址的代码

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

    return $realip;
}