PHP Constant Examples

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;