PHP defined() Function
The PHP defined() function is used to check whether the given constant exists and is defined.
Note: To check if a variable exists, use isset() as defined() only applies to constants. To check if a function exists, use function_exists().
Syntax
defined(constant_name)
Parameters
constant_name |
Required. Specify the name of the constant. |
Return Value
Returns true if the named constant given by constant_name has been defined, false otherwise.
Example: checking constants
The example below shows the usage of defined() function.
<?php
//defining few constants
const x = 100;
define("Greeting", "Hello world!");
class foo {
const test = "Hello";
}
//checking if a given constant exists
var_dump(defined("x"));
var_dump(defined("Greeting"));
var_dump(defined("foo::test"));
echo "\n";
var_dump(defined("y"));
var_dump(defined("GREETING"));
var_dump(defined("foo::test1"));
?>
The output of the above code will be:
bool(true) bool(true) bool(true) bool(false) bool(false) bool(false)
❮ PHP Miscellaneous Reference
