Constants in PHP | PHP Tutorial

Constants in PHP represents those values which can’t be changed after initialization within a script.

Constants in PHP are case-sensitive, by default.

Constant names must start with an alphabet or underscore.

How to define constants in PHP ?

Constants can be defined using define() method. It has following definition –

define(name,value,case-insensitivity)

Parameters –

– name : The name of constant

– value : Value of constant

– case-insensitivity : if set to true, the constant will become case-insensitive. Default is false and it is optional parameter.

Example

Creating a constant with case-sensitive name-

<?php
define("WELCOME", "Welcome to CodingLessons.info!");
echo WELCOME.' is constant';
?>

In the above example, constant declared is case-sensitive, it means you cannot access this constant using ‘Welcome’ or ‘weclome’ or ‘weLcome’ etc. This will generate error that CONSTANT is not defined.

Declaring case-insensitive constants –

<?php
define("WELCOME", "Welcome to CodingLessons.info!","true");
echo welcome.' is constant';
?>

In this example, the constant ‘welcome’ is defined case-insensitive, that means we can access it using ‘Welcome’ or ‘welcome’ etc.

Constants Vs Variables

 – There is no need to use $ sign in constants .

 – Constants cannot be declared in simple expressions, define() function is used.

 – Constants are global and can be accessed anywhere.

 – Once the constant is defined, it’s value must not be changed.

Scopes of Constants

Unlike, declaring variables, constants are having global scopes. It means, a constant once declared, can be used anywhere within the script.