PHP defined() function
This function is used to check the existence of a constant. It returns a boolean value.
Syntax
defined(const_name);
const_name is the constant name. If constant exists, then it returns TRUE, otherwise FALSE.
Example
<?php
define("SITE", "eTutorials Point");
if(defined(SITE)){
echo SITE;
}
else{
echo 'Constant is not defined';
}
?>
Output of the above code -
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