PHP Constants

PHP constants

PHP constants are name or identifier that can't be changed during the execution of the script.

PHP constants can be defined by 2 ways:

  • Using define() function
  • Using const keyword

PHP constants follow the same PHP variable rules. For example, it can be started with letter or underscore only.
Conventionally, PHP constants should be defined in uppercase letters.


PHP constant: define()

Let's see the syntax of define() function in PHP.

define(name, value, case-insensitive)  

  • name: specifies the constant name
  • value: specifies the constant value
  • case-insensitive: Default value is false. It means it is case sensitive by default.
  • Let's see the example to define PHP constant using define().

<?php  
    define("MESSAGE","Hello w3professors");  
    echo MESSAGE;  
?>  
Output : Hello w3professors

True Condition

<?php  
    define("MESSAGE","Hello W3professores",true);//not case sensitive  
    echo MESSAGE;  
    echo message;  
?>
Output : Hello W3professors

False Condition

<?php  
    define("MESSAGE","Hello W3professors",false);//case sensitive  
    echo MESSAGE;  
    echo message;  
?>  
Output : Hello W3professors
Notice : Use of undefined constant message - assumed 'message' in C:\wamp\www\vconstant3.php on line 4 message

PHP constant: const keyword

The const keyword defines constants at compile time. It is a language construct not a function.

  • It is bit faster than define().
  • It is always case sensitive.
  • <?php  
        const MESSAGE="Hello const by w3professors PHP";  
        echo MESSAGE;  
    ?>  
    
    Output : Hello const by w3professors PHP