Resources

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.
Converting to resource
As 
resource variables hold special handles to opened files, database connections, image canvas areas and the like, converting to a 
resource makes no sense.
Freeing resources
Thanks to the reference-counting system being part of the 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.