defined

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

defined — Checks whether a constant with the given name exists

Опис

defined(string $constant_name): bool

Checks whether a constant with the given constant_name is defined.

This function works also with class constants and enum cases.

Зауваження:
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().

Параметри

constant_name: The constant name.

Значення, що повертаються

Returns true if the named constant given by constant_name has been defined, false otherwise.

Приклади

Приклад #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)

?>

Приклад #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)

?>

Прогляньте також

define() - Defines a named constant
constant() - Returns the value of a constant
get_defined_constants() - Returns an associative array with the names of all the constants and their values
function_exists() - Return true if the given function has been defined
The section on Constants