What is the constant() function in PHP?

The constant() function returns the value of a constant when you have the name of the constant as a string. It is useful when the constant name is stored in a variable or created at run time.

<?php
define("SITE_NAME", "Tutorials Class");

class App {
    const VERSION = "2.0";
}

echo constant("SITE_NAME") . "<br>";

$name = "SITE_NAME";
echo constant($name) . "<br>";

echo constant("App::VERSION");
?>

Output:

If the constant does not exist, PHP 8 throws an Error. Check it first with defined(). Read PHP Constants for the basics.

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