先來了解一個變量的含義：

$_SERVER['REMOTE_ADDR']：瀏覽當前頁面的用戶計算機的ip地址

$_SERVER['HTTP_CLIENT_IP']：客戶端的ip

$_SERVER['HTTP_X_FORWARDED_FOR']：瀏覽當前頁面的用戶計算機的網關

$_SERVER['HTTP_X_REAL_IP']：nginx 代理模式下，獲取客戶端真實IP

/**
 *  獲取客戶端IP地址
 */
function real_ip()
{
    $ip = $_SERVER['REMOTE_ADDR'];
    if (isset($_SERVER['HTTP_X_FORWARDED_FOR']) && preg_match_all('#\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}#s', $_SERVER['HTTP_X_FORWARDED_FOR'], $matches)) {
        foreach ($matches[0] AS $xip) {
            if (!preg_match('#^(10|172\.16|192\.168)\.#', $xip)) {
                $ip = $xip;
                break;
            }
        }
    } elseif (isset($_SERVER['HTTP_CLIENT_IP']) && preg_match('/^([0-9]{1,3}\.){3}[0-9]{1,3}$/', $_SERVER['HTTP_CLIENT_IP'])) {
        $ip = $_SERVER['HTTP_CLIENT_IP'];
    } elseif (isset($_SERVER['HTTP_CF_CONNECTING_IP']) && preg_match('/^([0-9]{1,3}\.){3}[0-9]{1,3}$/', $_SERVER['HTTP_CF_CONNECTING_IP'])) {
        $ip = $_SERVER['HTTP_CF_CONNECTING_IP'];
    } elseif (isset($_SERVER['HTTP_X_REAL_IP']) && preg_match('/^([0-9]{1,3}\.){3}[0-9]{1,3}$/', $_SERVER['HTTP_X_REAL_IP'])) {
        $ip = $_SERVER['HTTP_X_REAL_IP'];
    }
    return $ip;
}