PHP’s Magic Constants: __LINE__ , __FILE__, __FUNCTION__, __CLASS__, and __METHOD__
Setting constants in PHP is as easy as using the define function, but PHP creates a few constants in every script for you that help mostly for debugging purposes (well, that's generally the only time I use them). These constants are called "magic constants."
Magic constants have a funny syntax, placing two underscores before and after the constant's word representation. These are PHP's magic constants:
__LINE__
__FILE__
__FUNCTION__
__CLASS__
__METHOD__
You can imagine how helpful these constants are for debugging...but if you can't:
if($sugar == '') { echo('$sugar has no value on line '.__LINE__.' of ['.__FILE__.']'); }
There are also helpful uses for these magic constants:
dirname(__FILE__) // get the directory name of the current script
What do you use them for?
![Send Text Messages with PHP]()
Kids these days, I tell ya. All they care about is the technology. The video games. The bottled water. Oh, and the texting, always the texting. Back in my day, all we had was...OK, I had all of these things too. But I still don't get...
![fetch API]()
One of the worst kept secrets about AJAX on the web is that the underlying API for it, XMLHttpRequest, wasn't really made for what we've been using it for. We've done well to create elegant APIs around XHR but we know we can do better. Our effort to...
![Animated AJAX Record Deletion Using Dojo]()
I'm a huge fan of WordPress' method of individual article deletion. You click the delete link, the menu item animates red, and the item disappears. Here's how to achieve that functionality with Dojo JavaScript.
The PHP - Content & Header
The following snippet goes at the...
![jQuery UI DatePicker: Disable Specified Days]()
One project I'm currently working on requires jQuery. The project also features a datepicker for requesting a visit to their location. jQuery UI's DatePicker plugin was the natural choice and it does a really nice job. One challenge I encountered was the...
My two favorite are
That you can use it to get parent directory:
or you can include the init.php file from anywhere in your filesystem:
You would use
in the init.php
Wow, awesome usage of the __FILE__ magic constant — I hadn’t thought of that one!
Useful!
To Jesus DeLaTorre:
Maybe it could be better, when you use this:
$dir = str_replace ( “\”, “/”, dirname ( _FILE_ ) )
-> for Windows based systems
(PS: nice book engine)
thanks for this, i knew only __FILE__ so i googled this article :)
@jeezaa:
Instead of
/for linux and\for windows, just use another constant:omg @ the comments
realpath(dirname(__FILE__)) or
__DIR__ or
realpath(dirname(__FILE__).’/..’).’/file.bla’
is there any way to get the constants defined in a php file using
define()?
Yes there is. The function get_defined_constants() shows you all of the defined constants see: http://www.php.net/manual/en/function.get-defined-constants.php.
I have never seen the use of __FUNCTION__
Can give me any Example.
I make it a habit to wrap these magic constants into SQL and PL/SQL blocks so that I can quickly trace the construction of queries and DML to the source.
There’s also the
__NAMESPACE__constant, e.g.namespace hyperdrive; add_action('wp_head', __NAMESPACE__ .'\engage');