PHP Constants

A PHP constant is a named identifier (name) that holds a fixed value throughout your script's execution. Unlike variables, constants cannot be changed once defined.

• Improved code readability and maintainability: Meaningful names for constants enhance code comprehension and reduce errors.

• Increased efficiency: Predefined values can be accessed faster than calculated values.

• Enhanced security: Sensitive information can be stored securely in constants instead of hardcoded variables.

• Create a PHP Constant

To create a constant, 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.

Example

Create a constant with a case-sensitive name:

<!DOCTYPE html>
<html>
<body>

<?php
// case-sensitive constant name
define("GREETING", "Welcome to codelines!");
echo GREETING;
?> 

</body>
</html>

Output

Welcome to codelines!

Example

Create a constant with a case-insensitive name:

<!DOCTYPE html>
<html>
<body>

<?php
// case-sensitive constant name
define("GREETING", "Welcome to codelines!");
echo GREETING;
?> 

</body>
</html>

Output

Welcome to codelines!

• PHP const Keyword

You can also create a constant by using the const keyword.

Example

Create a constant with the const keyword:

<!DOCTYPE html>
<html>
<body>

<?php
const MYCAR = "Codelines!";

echo MYCAR;
?> 

</body>
</html>

Output

Codelines!

const vs. define()

• const are always case-sensitive
• define() has has a case-insensitive option.
• const cannot be created inside another block scope, like inside a function or inside an if statement.
• define can be created inside another block scope.

• PHP Constant Arrays

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

Example

<!DOCTYPE html>
<html>
<body>

<?php
define("cars", [
  "Alfa Romeo",
  "BMW",
  "Toyota"
]);
echo cars[0];
?> 

</body>
</html>

Output

Alfa Romeo

• Constants are Global

This example uses a constant inside a function, even if it is defined outside the function:

Example

<!DOCTYPE html>
<html>
<body>

<?php
define("GREETING", "Welcome to Codelines.in!");

function myTest() {
  echo GREETING;
}
 
myTest();
?> 

</body>
<html>

Output

Welcome to Codelines.in!