defined
(PHP 4, PHP 5, PHP 7, PHP 8)
Checks whether a constant with the given name exists
Description
Checks whether a constant with the given constant_name is defined.
This function works also with class constants and enum cases.
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().
Parameters
constant_nameThe constant name.
Notedefined()takes the name as an ordinarystringand does not resolve it against the current namespace: the name is looked up in the global namespace, so an unqualified name may silently report on a different constant from the one the same bare identifier would refer to. To check whether a constant declared in a namespace is defined, the namespace must be part of the name, as indefined('My\Namespace\MYCONST')ordefined(__NAMESPACE__ . '\MYCONST'). Because the name is a plain string, aliases introduced byusestatements and thenamespace\prefix are not applied to it. In a double-quoted string the namespace separators must be escaped, as in"My\\Namespace\\MYCONST". The namespace part of the name is case-insensitive, the constant name is not.
Return Values
Returns true if the named constant given by constant_name has been defined, false otherwise.
Examples
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)
?>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)
?>