(PHP 4, PHP 5, PHP 7)
defined — Checks whether a given named constant exists
$name
) : boolChecks whether the given constant exists and is defined.
Note:
If you want to see if a variable exists, use isset() as defined() only applies to constants. If you want to see if a function exists, use function_exists().
nameThe constant name.
Returns TRUE if the named constant given by name
has been defined, FALSE otherwise.
Example #1 Checking Constants
<?php
/* Note the use of quotes, this is important. This example is checking
* if the string 'TEST' is the name of a constant named TEST */
if (defined('TEST')) {
echo TEST;
}
?>