To retrieve a pointer to a currently installed callback, call ct_callback with the parameter action as CS_GET. ct_callback sets *func to the address of the current callback. An application saves this address for reuse at a later time.
To deinstall a callback, call ct_callback with the parameter action as CS_SET and func as NULL.
To replace an existing callback routine with a new one, call ct_callback to install the new routine. ct_callback replaces the existing callback with the new callback.
