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(PHP 4, PHP 5, PHP 7, PHP 8)
defined — Checks whether a constant with the given name exists
Checks whether a constant with the given constant_name
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.
Note:
defined() takes the name as an ordinary string and 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 in
defined('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.
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)
?>
