How do I read values (PHP defined constants) from wp-config.php?

Question

I need to get username, password etc from the wp-config file to connect to a custom PDO database.

Currently I have another file where I have this info, but

Answer 1

I would just include the file then I would have access to the variable in it varibales.

This is assuming you're on the same server and you can access wp-config.php through the file system.

If you're doing this for a plugin, these values are already available. You won't need to include the file again.