defined
(PHP 4, PHP 5, PHP 7)
defined — Checks whether a given named constant exists
Description
bool defined ( string $name )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
← define
die →
? 1997–2017 The PHP Documentation GroupLicensed under the Creative Commons Attribution License v3.0 or later.
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