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.
注: The resource type was introduced in PHP 4
As resource types hold special handlers to opened
files, database connections, image canvas areas and the
like, you cannot convert any value to a resource.
Due to the reference-counting system introduced with
PHP4's Zend-engine, it is automatically detected when a
resource is no longer referred to (just like Java). When
this is the case, all resources that were in use for this
resource are made free by the garbage collector. For this
reason, it is rarely ever necessary to free the memory
manually by using some free_result function.
注: Persistent database links are special, they are not destroyed by the garbage collector. See also the section about persistent connections.