A constant is a name or an identifier that can’t be changed during the execution of the script (except magic constants). A valid PHP constant name starts with a letter or underscore (no $ sign before the constant name).There are two way to defined PHP Constants which is given below:

  1. Using define()function
  2. Using const keyword



1. Using define() function

Syntax:

define(name, value, case-insensitive)

Where:

  • name: denote the constant name
  • value: denote the constant value
  • case-insensitive: Default value is false. So we can say it is case sensitive by default.

Example

with a case-sensitive name:

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

Output:

Welcome to Netzole.com!


Example

with a case-insensitive name:

<?php 
  
define("CHEERFUL", "Welcome to Netzole.com!", true);
echo cheerful;
  
?> 

Output:

Welcome to Netzole.com!


PHP Constant Arrays

Example

with a Array constant:

<?php 
define("cars", [
    "Audi",
    "BMW",
    "Toyota"
]);
echo cars[1];
?> 

Output:

Audi




2. Using const keyword

The const keyword defines constants at compile time. It is a language construct not a function.It is bit faster than define() and It is always case sensitive.

Example

with a case-sensitive name:

<?php  
const MESSAGE="Welcome to Netzole.com!";  
echo MESSAGE;  
?>  

Output:

Welcome to Netzole.com!

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