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

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

 

Example

 

<!DOCTYPE html>
<html>
<body>

<?php
// case-sensitive constant name
define(“GREETING”, “Welcome to robertkaramagi.wordpress.com!”);
echo GREETING;
?>

</body>
</html>

 

Output

 

 

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

 

Example

 

<!DOCTYPE html>
<html>
<body>

<?php
// case-insensitive constant name
define(“GREETING”, “Welcome to robertkaramagi.wordpress.com!”, true);
echo greeting;
?>

</body>
</html>

 

Output

 

 

Constants are Global

 

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:

Example

 

<!DOCTYPE html>
<html>
<body>

<?php
define(“GREETING”, “Welcome to robertkaramagi.wordpress.com!”);

function myTest() {
echo GREETING;
}

myTest();
?>

</body>
</html>

 

Output