defined
Description
bool defined ( string name)Returns TRUE if the named constant given by name has been defined, FALSE otherwise.
Example 1. Checking Constants
<?php
/* Note the use of quotes, this is important. This example is checking
* if the string 'CONSTANT' is the name of a constant named CONSTANT */
if (defined('CONSTANT')) {
echo CONSTANT;
}
?>
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().
See also define(), constant(), get_defined_constants(), function_exists(), and the section on Constants.
