PHP 5 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

The example below creates a constant with a case-sensitive name:

<?php
define("GREETING", "Welcome to w3ii.com!");
echo GREETING;
?>

The example below creates a constant with a case-insensitive name:

<?php
define("GREETING", "Welcome to w3ii.com!", true);
echo greeting;
?>

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

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

<?php
define("GREETING", "Welcome to w3ii.com!");

function myTest() {
echo GREETING;
}

myTest();
?>