As indicated by the name, this function will return the value of the constant. This is useful when you want to retrieve value of a constant, but you do not know its name, i.e. It is stored in a variable or returned by a function.

<?php

define("GlobalGuideline", 50);

echo GlobalGuideline;

echo constant("GlobalGuideline"); // same thing as the previous line

?>

Only scalar data (boolean, integer, float and string) can be contained in constants.