What is an .inc and why use it?

Question

It has no meaning, it is just a file extension. It is some people's convention to name files with a .inc extension if that file is designed to be included by other PHP files, but it is only convention.

It does have a possible disadvantage which is that servers normally are not configured to parse .inc files as php, so if the file sits in your web root and your server is configured in the default way, a user could view your php source code in the .inc file by visiting the URL directly.

Its only possible advantage is that it is easy to identify which files are used as includes. Although simply giving them a .php extension and placing them in an includes folder has the same effect without the disadvantage mentioned above.

If you are concerned about the file's content being served rather than its output. You can use a double extension like: file.inc.php. It then serves the same purpose of helpfulness and maintainability.

I normally have 2 php files for each page on my site:

1. One named welcome.php in the root folder, containing all of the HTML markup.
2. And another named welcome.inc.php in the inc folder, containing all PHP functions specific to the welcome.php page.

EDIT: Another benefit of using the double extention .inc.php would be that any IDE can still recognise the file as PHP code.

Generally means that its a file that needs to be included and does not make standalone script in itself.

This is a convention not a programming technique.

Although if your web server is not configured properly it could expose files with extensions like .inc.

It's just a way for the developer to be able to easily identify files which are meant to be used as includes. It's a popular convention. It does not have any special meaning to PHP, and won't change the behaviour of PHP or the script itself.

This is a convention that programmer usually use to identify different file names for include files. So that if the other developers is working on their code, he can easily identify why this file is there and what is purpose of this file by just seeing the name of the file.

Just to add. Another disadvantage would be, .inc files are not recognized by IDE thus, you could not take advantage of auto-complete or code prediction features.