PHP Constants

Constants in PHP are like variables that contains value, but once they are defined they cannot be changed or undefined.

Constants are case-sensitive.

By convention, constant identifiers are always uppercase.

A valid constant name starts with a letter or underscore (no $ sign before the constant name).

Create a PHP Constant

To create a constant, we use the define() function.

Syntax

define(name, value, case-insensitive)

Parameters:

• name: Specifies the name of the constant
• value: Specifies the value of the constant
• case-insensitive: Specifies whether the constant name should be case-insensitive. by default it takes false.

Example:

Creating a constant with a case-sensitive name:

<?php
define("SOLVPROG", "Welcome to Solvprog.com! PHP Tutorials");
echo SOLVPROG;
?>

Output: a constant with a case-sensitive name

Output: PHP Constants

Example:

Creating a constant with a case-insensitive name:

<?php
define("SOLVPROG", "Welcome to Solvprog.com! PHP Tutorials", true);
echo solvprog;
?>

Output: a constant with a case-insensitive name

Output: PHP Constants

PHP Constant Arrays

In PHP7, you can create an Array constant using the define() function.

Example:

<?php
define("brands", [
  "Google",
  "Nike",
  "Coca Colla"
]);

echo brands[0]. ", " . brands[1] . " & " . brands[2];

?>

Output:

Constants are Global

Constants are automatically global and can be used across the entire script.

Example

This example uses a constant inside a function, and also it is defined outside the function:

<?php
define("SUCCESS", "You define your own success!");

function quotes() {
  echo SUCCESS;
}
 
quotes(); // output: You define your own success!
?>

Output: