Like in other programming languages, a constant in PHP is an identifier for a fixed value. Unlike a variable, a constant is defined once and its value can’t be changed during an app’s lifecycle.
A valid constant name starts with a letter or underscore. It doesn’t start with a dollar sign ($) like a variable.
Create a PHP Constant
We use define()
function to create a constant.
define(name, value, case-insensitive)
//define a constant define("WEB_ROOT", "https://www.tldevtech.com/"); //usage echo "The root URL is ".WEB_ROOT; function displayRoot(){ echo WEB_ROOT; }
Starting from PHP7, you can create an Array constant. The define()
method is still used for array constant definition. The array then can be called a normal one. The only difference is that its values are final.
define("phones", [ "Samsung", "Apple" ]); echo phones[0]; //Samsung
Create a PHP Class Constant
We can use constants in a class. However, it needs another approach to define and call a class constant.
class Phone { const COUNTRY = 'Korea'; function showOrigin() { echo self::COUNTRY; } } $phone = new Phone(); $class->showOrigin(); echo $class::COUNTRY;