Possible issue with PHP config?

The notice error is because you are accessing an array like $someArray[DB_HOST]. Array keys should have quotes around them like $someArray['DB_HOST']. No quotes is a constant and keys are strings, not constant.

The include path issue is pretty standard too. If you have the following files:

index.php
includes/config.php
includes/include.php

If you load index.php and include the file includes/include.php you will have to type the full path includes/include.php. If inside of include.php you want to include includes/config.php. php treats the path as relative to where the original script is loaded which was index.php. Think about it like:

• In script, you load and run index.php.
• In index.php you include includes/include.php. This doesn't move you to includes/include.php but rather gets includes/include.php and brings the code into index.php
• All the code from includes/include.php runs as if from within index.php.
• You include includes/config.php. You are still technically in index.php and so you have to reference the file as if calling from within index.php.

To fix the include path, you can use the set_include_path function and add the full path to the includes directory (or relative to includes) and then you can drop the includes/ from the path. PHP will just check if the file is in includes/ if it can't find it anywhere else. You can also just change the include_path directive in php.ini or an .htaccess file.

Usually PHP core setting include_path contains the current path as well: it's denoted by . (a dot), added to a list of included pathes:

include_path=".;c:\php\includes"

Quoting the doc:

Using a . in the include path allows for relative includes as it means the current directory. However, it is more efficient to explicitly use include './file' than having PHP always check the current directory for every include.

And yes, any barename (a non-quoted string) will be processed as a constant name by PHP. If this constant is not defined (like in your case), PHP will convert it to a string (issuing a notice, though).