为什么不在PHP中显示错误信息？

This is my php code for connecting database:

config.php:

<?php
ob_start();
error_reporting( E_ALL & ~E_NOTICE);
require_once("constants.php");
if (version_compare(PHP_VERSION, 5.3, '<') && function_exists('set_magic_quotes_runtime')) set_magic_quotes_runtime(0);
$currentPage = pathinfo($_SERVER['PHP_SELF'], PATHINFO_FILENAME);
$conn=mysql_connect(DB_SERVER, DB_SERVER_USERNAME, DB_SERVER_PASSWORD) or die("sorry! could not connect<br><b>".mysql_error()."</b>");
if($connn) {
mysql_select_db(DB_DATABASE) or die("sorry! could not connect with database <br><b>".mysql_error()."</b>");
}
?>

constants.php:

<?php
define('HTTP_SERVER', 'http://localhost');
define('SITE_DIR', '/selva/');
define('DB_PREFIX', 'mypage1_');
define('DB_SERVER', 'localhost');
define('DB_SERVER_USERNAME', 'root');
define('DB_SERVER_PASSWORD', '');
define('DB_DATABASE', 'vkls8');
define('SITE_NAME', 'selva');
define('TABLE_PAGES', DB_PREFIX.'pages');
define('TABLE_TAGLINE', DB_PREFIX.'tagline');
?>

index.php:

<?php
require("libs/config.php");
?>

Now i have entered incorrect database name. but when run this code, it shows nothing. May i know why?. It needs to display 'could not connect with database' right?.. May i know is there any missing in my code.

Can anybody fix this? Thanks in advance.

try using this..

index.php:

<?php
require("libs/config.php");
$output = ob_get_contents();
ob_end_clean();
echo $otuput;
?>

OR comment out ob_start();