获取客户端IP地址函数

function get_ip()
{
    static $ip = NULL;
    if($ip !== NULL){return $ip;}
    if(isset($_SERVER)) {if(isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {$arr = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
            foreach ($arr as $ip) {$ip = trim($ip);
                if($ip != 'unknown') {
                    $ip = $ip;
                    break;
                }
            }
        } elseif(isset($_SERVER['HTTP_CLIENT_IP'])) {$ip = $_SERVER['HTTP_CLIENT_IP'];
        } else {if(isset($_SERVER['REMOTE_ADDR'])) {$ip = $_SERVER['REMOTE_ADDR'];
            } else {$ip = '0.0.0.0';}
        }
    } else {if(getenv('HTTP_X_FORWARDED_FOR')) {$ip = getenv('HTTP_X_FORWARDED_FOR');
        } elseif(getenv('HTTP_CLIENT_IP')) {$ip = getenv('HTTP_CLIENT_IP');
        } else {$ip = getenv('REMOTE_ADDR');
        }
    }
    preg_match("/[\d\.]{7,15}/", $ip, $onlineip);
    $ip = !empty($onlineip[0]) ? $onlineip[0] : '0.0.0.0';

    return $ip;
}