A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions. See the appendix for a listing of all these functions and the corresponding resource types.
See also the get_resource_type() function.
As resource variables hold special handlers to opened files, database connections, image canvas areas and the like, converting to a resource makes no sense.
Thanks to the reference-counting system introduced with PHP 4's Zend Engine, a resource with no more references to it is detected automatically, and it is freed by the garbage collector. For this reason, it is rarely necessary to free the memory manually.
Note: Persistent database links are an exception to this rule. They are not destroyed by the garbage collector. See the persistent connections section for more information.