php constant

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

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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.

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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

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