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.
Create a PHP Constant
To create a constant, use the define() function.
Syntax
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
Example
Create a constant with a case-sensitive name:
<?php
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
?>
Try it Yourself »
Example
Create a constant with a case-insensitive name:
<?php
define("GREETING", "Welcome to W3Schools.com!", true);
echo greeting;
?>
Try it Yourself »
PHP Constant Arrays
In PHP7, you can create an Array constant using the define() function.
Example
Create an Array constant:
<?php
define("cars", [
"Alfa Romeo",
"BMW",
"Toyota"
]);
echo cars[0];
?>
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Constants are Global
Constants are automatically global and can be used across the entire script.
Example
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();
?>
Try it Yourself »
