The Dynamic Data Exchange Management Library (DDEML) makes it possible for a server application to register the service names that it supports and to prevent the DDEML from sending XTYP_CONNECT transactions for unsupported service names to the server's Dynamic Data Exchange (DDE) callback function.
The following topics describe the name service.
Service Name Registration
By registering its service names with the DDEML, a server informs other DDE applications in the system that a new server is available. A server registers a service name by calling the DdeNameService function and specifying a string handle that identifies the name. In response, the DDEML sends an XTYP_REGISTER transaction to the callback function of each DDEML application in the system (except those that specified the CBF_SKIP_REGISTRATIONS filter flag in the DdeInitialize function). The XTYP_REGISTER transaction passes two string handles to a callback function: the first identifies the string specifying the base service name, and the second identifies the string specifying the instance-specific service. A client typically uses the base service name in a list of available servers, so the user can select a server from the list. The client uses the instance-specific service name to establish a conversation with a specific instance of a server application, if more than one instance is running.
A server can use DdeNameService to unregister a service name. This function causes the DDEML to send XTYP_UNREGISTER transactions to the other DDE applications in the system, informing them that they can no longer use the name to establish conversations.
A server must call DdeNameService to register its service names soon after calling DdeInitialize. A server must unregister its service names by using DdeNameService just before calling the DdeUninitialize function.
Service Name Filter
In addition to registering service names, DdeNameService enables a server to turn its service name filter on or off. When a server turns off its service name filter, the DDEML sends the XTYP_CONNECT transaction to the server's DDE callback function whenever any client calls the DdeConnect function, regardless of the service name specified in the function. When a server turns on its service name filter, the DDEML sends the XTYP_CONNECT transaction to the server only when DdeConnect specifies a service name the server has specified in a call to DdeNameService.
By default, the service name filter is on when an application calls DdeInitialize. This default prevents the DDEML from sending the XTYP_CONNECT transaction to a server before the server has created the string handles it needs. A server can turn off its service name filter by specifying the DNS_FILTEROFF flag in a call to DdeNameService. The DNS_FILTERON flag turns on the filter.