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?
![Responsive Images: The Ultimate Guide]()
Chances are that any Web designers using our Ghostlab browser testing app, which allows seamless testing across all devices simultaneously, will have worked with responsive design in some shape or form. And as today's websites and devices become ever more varied, a plethora of responsive images...
![CSS 3D Folding Animation]()
Google Plus provides loads of inspiration for front-end developers, especially when it comes to the CSS and JavaScript wonders they create. Last year I duplicated their incredible PhotoStack effect with both MooTools and pure CSS; this time I'm going to duplicate...
![Multiple File Upload Input]()
More often than not, I find myself wanting to upload more than one file at a time. Having to use multiple "file" INPUT elements is annoying, slow, and inefficient. And if I hate them, I can't imagine how annoyed my users would be. Luckily Safari, Chrome...
![Prevent Page Zooming in Mobile Browsers]()
Ever since I got my iPhone, I've been more agreeable in going places that my fiancee wants to go. It's not because I have any interest in checking out women's shoes, looking at flowers, or that type of stuff -- it's because my iPhone lets...
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');