What should I name my PHP class file?

What are your coding standards?

It’s common to start class names with a capital letter (for example: class MyClass). If you do this, then it follows that you would name the file MyClass.php. And MyClass.class.php works too.

MyClass.class is a bad idea that could allow someone to view your source code if they request that file by name. Using the .php extension ensures that the the user will only see the output after the file is processed by the PHP interpreter which—for a file that contains nothing but a class—is a blank page.

Finally, look into autoload(), which saves you the trouble of calling require_once in order to load your class.

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Update: With PHP coding standard PSR-4, there is now a semi-official way to name your class files. The previous advice—to name your class file the same as the class with the .php extension—still stands. But now you are expected to place that class file in a subdirectory named after your class namespace; PSR-4 requires that all of your classes be contained in a namespace defined by you.

What do you get for this? Autoloading for free! If you’re using Composer, you can specify the top-level directory for your classes and Composer will autoload them. No more require statements to load your classes.

If you don’t want to do this, you don’t have to: PSR-4 is a recommendation, not a requirement.

There is no difference beyond what you see. The ones with .class are helpful if you use autoloading and don't have a specific directory where your class files live. Otherwise, it's entirely arbitrary. (I used to use ClassName.class.php.)

I prefer MyClass.php - the exact same name (including capitals) as the class.

However, if you are working on an existing project, you should use whatever naming scheme the project has.