<?php
define('DRUPAL_ROOT',$_SERVER['DOCUMENT_ROOT']);includes/bootstrap.inc file
require_once DRUPAL_ROOT.'includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
global $user;

if(user_is_logged_in()){
    echo "logged";
} else {
    echo "not logged";
}
?>

object(stdClass)#17 (4) {
  ["uid"]=>
  int(0)
  ["hostname"]=>
  string(12) "XXX.XXX.XX.X"
  ["roles"]=>
  array(1) {
    [1]=>
    string(14) "anonymous user"
  }
  ["cache"]=>
  int(0)
}