Best way to find this is: create a php file and add the following code:
<?php phpinfo(); ?> and open it in browser, it will show the file which is actually being read!
Updates by OP:
- The previously accepted answer is likely to be faster and more convenient for you, but it is not always correct. See comments on that answer.
- Please also note the more convenient alternative
<? php_ini_loaded_file(); ?>mentioned in this answer.