DDE Links

You need a DDE data link whenever a client program needs to know about changes to the value of a particular data item in the server application. You can establish a DDE data link in LabWindows/CVI by calling SetUpDDEWarmLink or SetUpDDEHotLink. Whenever the data value changes, the DDE_DATAREADY message invokes the client callback function, and the client receives the data, which is available in the dataPtr parameter.

Multiple data links, each of which applies to a different data item, can exist within one client-server connection. For example, you can establish a link between your LabWindows/CVI program and a particular cell in Excel. You specify the data item to which the link applies in the itemName parameter of SetUpDDEWarmLink or SetUpDDEHotLink.

As defined in Windows, warm and hot links differ in that under a warm link, the client is merely alerted when the data value changes; whereas, under a hot link, the data is actually sent.

LabWindows/CVI makes no distinction between warm links and hot links. In both cases, your client application receives the data through the client callback function when the data value changes. If a warm link is in effect, LabWindows/CVI requests and receives the data from the server before the callback function is called. LabWindows/CVI provides both SetUpDDEWarmLink and SetUpDDEHotLink because some DDE server applications offer only one type of link.