This site is mobile accessible. Press the "Tap Here" button to use a different font-size.

Smartphone icons created by Freepik - Flaticon

2.5 PHP Constants

Constants are like variables except that once they are defined they cannot be changed or undefined.

PHP Constants

A constant is an identifier (name) for a simple value. The value cannot be changed during the script.
A valid constant name starts with a letter or underscore (no $ sign before the constant name).
Note: Unlike variables, constants are automatically global across the entire script.

To create a constant, use the define() function.

define(name, value, case-insensitive)

Parameters:
- name: Specifies the name of the constant
- value: Specifies the value of the constant
- case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false

Create a constant with a case-sensitive name:

<?php
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
?>

Create a constant with a case-insensitive name:

<?php
define("GREETING", "Welcome to W3Schools.com!", true);
echo greeting;
?>

In PHP7, you can create an Array constant using the define() function.

<?php
define("cars", [
  "Alfa Romeo",
  "BMW",
  "Toyota"
]);
echo cars[0];
?>

Constants are automatically global and can be used across the entire script.

This example uses a constant inside a function, even if it is defined outside the function:

<?php
define("GREETING", "Welcome to W3Schools.com!");

function myTest() {
  echo GREETING;
}
 
myTest();
?>

Eventually the navigation links, above, will be replaced by these << (previous) and >> (next) buttons below.

Module 2 quiz