包括、include_once、require 还是 require_once?

I have PHP file where I have defined the server access variables as well as the mysql_connect and mysql_select_db, as this functions are regularly used in almost every page in backend, while I am using include() which is perfectly working for me now, which method or function would you suggest and I would like to know if there is any flaw if I use include() or is it safe to use it?

Edit : Keeping in mind I'll be using $_SESSION variable too.

解决方案

The only difference between the two is that require and its sister require_once throw a fatal error if the file is not found, whereas include and include_once only show a warning and continue to load the rest of the page. If you don't want PHP to attempt to load the rest of your page without the database info (which I would assume), then use require_once. You don't need to include the file more than once, so there is no need to use the regular require function.