defined
(PHP 4, PHP 5, PHP 7, PHP 8)
defined — Checks whether a given named constant exists
Description
defined(string
$constant_name): boolChecks 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
-
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;
}
?>
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
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