What are Class Constants in PHP

Class Constants

Class constants are just like regular constants, except for the fact that they are declared on a class and therefore also accessed through this specific class. Just like with static members, double-colon operator are used to access a class constant. Here is a basic example:

<?php

class User

{

    const DefaultUsername = "Imran Khan";

    const MinimumPasswordLength = 6;

}

echo "The default username is " . User::DefaultUsername;

echo "The minimum password length is " . User::MinimumPasswordLength;

?>

Constants can be defined for some basic expressions whose values are always going to remain the same.

For example, defining constant using math expression:

<?php

class MyTimer {
    const SEC_PER_DAY = 60 * 60 * 24;
}

?>

Class constant can also be defined with an array. An example of such declaration is given below:

<?php
class MyClass
{
    const ABC = array('A', 'B', 'C');
    const A = '1';
    const B = '2';
    const C = '3';
}
var_dump(MyClass::ABC);

As it is clear that it's much like declaring variables, except there is no access modifier - a constant is always publically available. As required, we immediately assign a value to the constants, which will then stay the same all through execution of the program. To use the constant, we write the name of the class, followed by the double-colon operator and then the name of the constant.