使用error_reporting和ini_set（Apache 2.2中的PHP模块）时未显示PHP错误

I am trying to use error_reporting() in order to show all errors in my php script

error_reporting(E_ALL); 
error_reporting(-1); 
ini_set('error_reporting', E_ALL);

However, while php errors are properly logged, none of the functions above show the errors in the page.

I know the error reporting can be properly set in the php.ini file (I know how to that), but I don't understand why it can't be changed on the fly using the standard php functions.

I am suspecting Apache not authorizing to do so (php is installed as a module, config file is in /etc/php5/apache2/php.ini )

Thanks for your help