Checking a port if it's in use/open

[wysota]

Yes, I just want to know if somebody or something use the port.

What fatjuicymole meant is that you can't have a service running on that port - i.e. you can't have a vnc daemon there. If that's acceptible then open a QTcpServer on that port and when something tries to connect to it, simply close the client socket to drop the connection.