Port(Connector &con, const char *name): This constructor assigns the connector reference to the external protected data member as described next and passes the name of the port to the base Connector constructor. The constructor of the Port class is protected so as to prevent actual objects of the class from being instantiated; only classes derived from Input and Output can be created.
Connector *external: This member represents the external connector to which the port itself is connected. This data member usually points to a port in an hierarchical level immediately above the port or to a wire in the same hierarchical level as the port. Note that because Wire and Port are both derived from the Connector class, external may point to either a Wire object or a Port object.