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defined

(PHP 4, PHP 5, PHP 7)

defined — Checks whether a given named constant exists

Description

defined ( string $name ) : bool

Checks whether the given constant exists and is defined.

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

name: The constant name.

Return Values

Returns true if the named constant given by 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;
}
?>

See Also

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

© 1997–2020 The PHP Documentation Group
Licensed under the Creative Commons Attribution License v3.0 or later.
https://www.php.net/manual/en/function.defined.php