The get_defined_constants Function

The get_defined_constants function returns an array with all currently defined constants. The function can take an optional parameter, which allows getting constants only of a specific category. The returned array contains constant names as keys and their values.

Syntax

get_defined_constants(bool $categorize = false);

Example

Get all defined constants:

<?php
	define('MY_CONST', 'test');
	$res = get_defined_constants();
	print_r(array_slice($res, 0, 3));
?>

Code execution result (first 3 elements):

[
	'E_ERROR' => 1,
	'E_WARNING' => 2,
	'MY_CONST' => 'test'
]

Example

Get constants grouped by categories:

<?php
	$res = get_defined_constants(true);
	print_r(array_keys($res));
?>

Code execution result (example):

[
	'Core',
	'pcre',
	'user'
]

Example

Check for the presence of a specific constant:

<?php
	$constants = get_defined_constants();
	if (isset($constants['PHP_VERSION'])) {
		echo 'PHP version: ' . $constants['PHP_VERSION'];
	}
?>

Code execution result (example):

'PHP version: 8.1.0'