PHP Constants

Constants are similar to variables, but once defined, their values cannot be changed or undefined throughout the script.

PHP Constants

A constant is a name for a simple value that remains the same during the script’s execution. A valid constant name starts with a letter or underscore (without a $ sign). Unlike variables, constants are automatically global across the entire script.

Creating a PHP Constant

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

Syntax

define(name, value);

define(name, value);

Parameters:

• name: Specifies the constant’s name.
• value: Specifies the constant’s value.

Example: Case-Sensitive Constant

define("WELCOME_MESSAGE", "Welcome to BikeZone!");
echo WELCOME_MESSAGE;

define("WELCOME_MESSAGE", "Welcome to BikeZone!");

echo WELCOME_MESSAGE;

Using the const Keyword

You can also create a constant using the const keyword.

Example: Case-Sensitive Constant with const Keyword

const BRAND = "Harley-Davidson";
echo BRAND;

const BRAND = "Harley-Davidson";

echo BRAND;

const vs. define()

• const cannot be created inside a block scope, such as within a function or an if statement.
• define can be created inside a block scope.

PHP Constant Arrays

From PHP 7 onwards, you can create an array constant using the define() function.

Example: Creating an Array Constant

define("BIKE_BRANDS", [
  "Harley-Davidson",
  "Yamaha",
  "Ducati"
]);
echo BIKE_BRANDS[0];

define("BIKE_BRANDS", [

  "Harley-Davidson",

  "Yamaha",

  "Ducati"

]);

echo BIKE_BRANDS[0];

Constants are Global

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

Example: Using a Constant Inside a Function

define("GREETING", "Welcome to BikeZone!");

function displayGreeting() {
  echo GREETING;
}

displayGreeting();

define("GREETING", "Welcome to BikeZone!");

​

function displayGreeting() {

  echo GREETING;

}

​

displayGreeting();