(PHP 4, PHP 5, PHP 7, PHP 8)
defined — Checks whether a given named constant exists
$constant_name): boolChecks whether the given constant exists and is defined.
This function works also with class constants and enum cases.
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().
constant_nameThe constant name.
Returns true if the named constant given by constant_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;
}
interface bar {
const test = 'foobar!';
}
class foo {
const test = 'foobar!';
}
var_dump(defined('bar::test')); // bool(true)
var_dump(defined('foo::test')); // bool(true)
?>
Example #2 Checking Enum Cases (as of PHP 8.1.0)
<?php
enum Suit
{
case Hearts;
case Diamonds;
case Clubs;
case Spades;
}
var_dump(defined('Suit::Hearts')); // bool(true)
?>