PHP Constants

PHP constants have a fixed value and it can not be changed during the execution of the script. It will be created using the define() function or const keyword.

In other words, a PHP constant is an identifier(name) that has a fixed value and it can not be changed or undefined except the magic constant.

  • Once the constant is defined, its value can not be changed. It means it has global scope although it defines within the function.
  • Please keep in mind that the PHP constant does not have a $ sign before the constant name
  • A PHP constant name should start with a letter or underscore (_).

How To Declare PHP Constants

PHP constant can be defined in two ways.

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

Creating PHP constant Using define() Function

To create a PHP constant function, use the define() function. It defines constant at the run time.

    define(name, value, case-insensitive);
  • name: It refers to a constant name.
  • value:It denotes constant value.
  • case-insensitive: Its default value is false. It denotes that the constant name is case-sensitive by default..

Source Code

echo WEBSITE;  
Try it now

Creating PHP Constant Using constant Keyword

PHP provides another way to create a constant using the const keyword. Please keep in mind that the const keyword defines constant at compile-time and the constant name is also case-sensitive.

Source Code

const WEBSITE="Learn PHP from sudhakarinfotech";  
echo WEBSITE;  
Try it now

PHP Constant Arrays

Let us create an array constant using the the define() function.

Source Code

define("cars", [
  "Honda City",
  "Maruti Suzki"
echo cars[0];
Try it now

How To Print Constant Value

There are two ways to display the constant value on the screen(browser).These are

  • 1.0 echo
  • 2.0 Constant() function

Constant() function

To display constant value, PHP also introduces a constant() function that is used to display the value of the constant.

General Syntax


Source Code

    echo WEBSITE, "</br>";  
    echo constant("WEBSITE");  
    //both are similar  
Try it now

Difference Between Constant And Variables

  • Variable has a dollar sign ($) before the name while the constant name does not have a $ sign before the constant name.
  • The variable value can be changed later but the constant value can not be changed.
  • Variable follows scope rule while constant can be accessed anywhere without regard to variable scoping rules.

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