PHP define() Function

The define() function is basically used by programmers to create constant. Constants in PHP are very similar to variables and the only difference between both are the values of constants can not be changed once it is set in a program. 

define() returns a Boolean  value. It will return TRUE on success and FALSE on failure of the expression.  

Syntax:

define(string $constant, mixed $value, bool $case_insensitive);

Parameters:

• $constant: It is of String type that describes the name of the constant and is a required parameter. 
• $value: It is of mixed type and it describes the Value of the constant and is required in parameter
• $case_insensitive: It is of a boolean type that describes whether the name of the constant can be case-sensitive or not and it is an optional parameter.

Return Value: This method returns a boolean value TRUE on success and FALSE on the failure of the expression.  

Example 1: In this example, we have created a constant namely GREETINGS  and its value is Hello GFG and the name of the constant is case-insensitive by using define() function.

PHP

<?php
    define("GREETINGS", "Hello GFG.", true);
    echo GREETINGS;
?>

Output

Hello GFG.

Example 2: In the below example, we have created a constant named as LANGUAGES which consist of an array as it’s value and the name of the constant is case-sensitive.

PHP

<?php
    define('LANGUAGES', array(
    'C',
    'C++',
    'JAVA',
    'PYTHON'
    ));

    echo LANGUAGES[3];
?>

Output

PYTHON

Reference: https://www.php.net/manual/en/function.define.php