send-request

Arguments: client-port item &key link timeout

Sends a DDE "Request" or "Advice" message to retrieve information from a DDE server for a particular item.

If link is :cold (which is the default), then the values returned by the DDE server application are synchronously returned from the call to send-request. If link is :warm or :hot, then send-request does not return an answer from the DDE server application, but instead starts an "advice" link with the server; whenever the server's value for the requested item has changed, the server asynchronously sends a message to Allegro CL, and the receive-advice method for this DDE port is then called with the values from the server. If link is :stop, then any advice link that was previously started for this item is stopped.

When unsuccessful, send-request returns nil. When successful, it returns a value from the DDE server for a :cold link, or t for a :warm, :hot, or :stop link. nil normally indicates that the DDE server does not support the particular request that was made.

The raw data buffer returned by the DDE server is first passed to the convert-returned-dde-buffer method for the port. That method should return a single value (perhaps constructing a list from multiple values that the server has encoded into the buffer), which is then either returned from send-request for a :cold link or passed to the port's receive-advice method for a :warm or :hot link. Refer to convert-returned-dde-buffer and convert-returned-dde-string for more information on converting the values from the server. If the request is unsuccessful, as when the server doesn't handle the requested item, then nil is returned.

Many applications that act as DDE servers implement a topic called system and an item called sysitems, and sometimes an item called topics, to which you can send a request to find out about additional topics.

See dde.htm for information about DDE support.

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This page was not revised from the 10.0 page.
Created 2019.8.20.