PHP Constants are non-volatile identifier or a name to store data. Unlike variables in PHP, we cannot modify a Constant value once they are defined. PHP Constants has global scope by default and can be used anywhere in the PHP program, including Functions, Classes, etc.
Naming Convention of PHP Constants
- A Constant name should start with alphabets and underscore.
- A Constant name should not start with
$symbol like Variables.
- A Constant cannot be changed once defined
- A Constant is a global scope identifier by default
How to create a PHP Constant
define(name, value, case-insensitive=TRUE|FALSE)
PHP Constant can be created using
define() function and
const keyword. By default constant is case-sensitive but by sending the third parameter’s value as
true we can make it case-insensitive. Also, when we use
const keyword to create a Constant, it’s case-sensitive as always. Please find below the examples,
<?php // using define() method define('SITE_NAME', "PHP Tutorials", true); echo SITE_NAME .'<br>'; echo site_name .'<br>'; // using const keyword const SITE_AUTHOR = "Admin"; echo SITE_AUTHOR .'<br>'; echo site_author; ?>
To retrieve the Constant, we can use
constant() method, based on the key we passed into this function, it will return the corresponding value.
<?php constant('SITE_NAME'); // returns "PHP Tutorials" constant('SITE_AUTHOR'); // returns "Admin" ?>
PHP Majic Constants
PHP Majic Constants are predefined constants that return the dynamic value based on where it has been used/called at the moment. It usually starts with two underscores at the beginning and the end like
__NAME__. Please find below a list of majic constants available in PHP.
|It returns the current line of the file.|
|It returns the full path along with the name of the file.|
|It returns the directory of the file.|
|It will return the name of the current function if it is called inside from the function.|
|It returns the name of the current Class.|
|It returns the name of the traits, including Namespace.|
|It returns the name of the current Class Method.|
|It returns the name of the current Namespace.|
When to use PHP Constants?
- If we are going to use certain Variables in multiple places across the scope of PHP, then we can declare PHP Constants.
- When we use MySql in PHP, we should use the database’s username/password in many places. In that scenario, we can assign these values into Constants and use them in the PHP program. If we want to change those credentials, we can change them in one place, and it reflects where ever we used those Constants.
- Usually, in many PHP Frameworks and WordPress CMS, we will use Constants for the global configurations. These configuration values will be used all over the project.
In this tutorial, we learned about PHP Constants and how to use them effectively, let’s jump into next chapter of this tutorial series.