PHP 5 Constants | php code

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

PHP Constants

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

Create a PHP Constant

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

Syntax

define(namevaluecase-insensitive)
Parameters:
  • name: Specifies the name of the constant
  • value: Specifies the value of the constant
  • case-insensitive: Specifies whether the constants name should be case-insensitive. Default is false
The example below create constants with a case-sensitive name:

Example

<?php
define("GREETING""Welcome to W3Schools.com!");
echo GREETING;
?>
Run example »
The example below create a constant with a case-insensitive name:

Example

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

Constants are Global

Constants are always global and can be used across the entire scripts.
Example below use  a constant inside a function, even if it is defined outside the function:

Example

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

function myTest() {
    echo GREETING;
}
 
myTest();
?>
Run example »

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