In this article, we will learn constants in PHP.
What are constants in PHP?
- Constants are used to store some value that remains unchanged during the execution of the program.
- We can declare constant using constant keyword followed by the name of the constant.
- The name of constant is case-sensitive, however, it is recommended in PHP to name the constant in upper-case letters.

How to access the constant value within the class?
We can get the value of constant within the class using the self keyword, a scope resolution operator :: and the name of the constant. Look at the following example.
<?php
class hello {
const MESSAGE = "Thank you for visiting PHP.org";
}
echo hellp::MESSAGE;
?>
How to access the constant value outside the class?
We can also get the value of constant outside the class. Write the name of the class, scope resolution operator :: and the name of the constant, Look at the following example.
<?php
class Hello {
const MESSAGE = "Thank you for visiting PHP.org";
public function tada() {
echo self::MESSAGE;
}
}
$hellp= new hello();
$hello->tada();
?>