How to use define in php

PHP define() function

Definition and usage

　The define() function defines a constant.

Constants are similar to variables, except that:

After setting, the value of the constant cannot be changed

The constant name does not require a leading dollar Symbol ($)

Scope does not affect access to constants

Constant values ​​can only be strings or numbers

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Syntax

define(name,value,case_insensitive)

Parameter	Description
name	Required. Specifies the name of the constant.
value	Required. Specifies the value of the constant.
case_insensitive	##Optional. Specifies whether constant names are case-sensitive. If set to true, it will not be case sensitive. Default is false (case sensitive).

Example

Example 1

Define a case-sensitive constant:

<?php
    define("GREETING","Hello world!");
    echo constant("GREETING");
?>

Output:

Hello world!

Example 2

Define a case-insensitive constant:

<?php
    define("GREETING","Hello world!",TRUE);
    echo constant("greeting");
?>

Output:

Hello world!

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