* The handle can come from the [[_OPENHOST]], [[OPENCLIENT]] or [[_OPENCONNECTION]] QB64 TCP/IP functions.
* Returns -1 if still connected or 0 if connection has ended/failed.
* Do not rely solely on this function to check for ending communication.
* Use "time-out" checking as well and [[CLOSE]] any suspect connections.
* If this function indicates the handle is not connected, any unread messages can still be read using [[GET (TCP/IP statement)|GET #]].
* Even if this function indicates the handle is not connected, it is important to [[CLOSE]] the connection anyway or important resources cannot be reallocated.