constant

Description

Return the value of the constant indicated by name.

constant() is useful if you need to retrieve the value of a constant, but do not know its name. I.e. it is stored in a variable or returned by a function.

This function works also with class constants and enum cases.

Parameters

name

The constant name.

Note

constant() takes the name as an ordinary string and does not resolve it against the current namespace: the name is looked up in the global namespace, so an unqualified name may silently return a different constant from the one the same bare identifier would refer to. To retrieve the value of a constant declared in a namespace, the namespace must be part of the name, as in constant('My\Namespace\MYCONST') or constant(__NAMESPACE__ . '\MYCONST'). Because the name is a plain string, aliases introduced by use statements and the namespace\ prefix are not applied to it. In a double-quoted string the namespace separators must be escaped, as in "My\\Namespace\\MYCONST". The namespace part of the name is case-insensitive, the constant name is not.

Return Values

Returns the value of the constant.

Errors/Exceptions

If the constant is not defined, an Error exception is thrown. Prior to PHP 8.0.0, an E_WARNING level error was generated in that case.

Changelog

Examples

Using constant() with Constants

<?php

define("MAXSIZE", 100);

echo MAXSIZE;
echo constant("MAXSIZE"); // same thing as the previous line


interface bar {
    const test = 'foobar!';
}

class foo {
    const test = 'foobar!';
}

$const = 'test';

var_dump(constant('bar::'. $const)); // string(7) "foobar!"
var_dump(constant('foo::'. $const)); // string(7) "foobar!"

?>

Using constant() with Enum Cases (as of PHP 8.1.0)

<?php

enum Suit
{
    case Hearts;
    case Diamonds;
    case Clubs;
    case Spades;
}

$case = 'Hearts';

var_dump(constant('Suit::'. $case)); // enum(Suit::Hearts)

?>

See Also

• define()
• defined()
• get_defined_constants()
• The section on Constants