PHP Manual: Checks whether a constant with the given name exists

Description

bool defined(string $constant_name)

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.

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)

?>

defined

Description

Parameters

Return Values

Examples

See Also