defined
Checks whether a constant with the given name exists
Description
bool defined(string $constant_name)
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.
Parameters
-
constant_name
-
The constant name.
Return Values
Returns true if the named constant given by constant_name
has been defined, false otherwise.
Examples
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)
?>
See Also
- define
- constant
- get_defined_constants
- function_exists
- The section on Constants