defined

(PHP 4, PHP 5, PHP 7, PHP 8)

definedChecks whether a given named constant exists

Description

defined(string $constant_name): bool

Checks 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().

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