Dynamic Data Exchange and IPC

Dynamic data exchange (DDE) is a protocol for interprocess communications that enables applications to exchange data in a variety of formats. Applications can use DDE for one-time data exchanges or for ongoing exchanges in which the applications update one another as new data becomes available.

The data formats used by DDE are the same as those used for the Windows clipboard IPC mechanism. DDE can be thought of as an extension of the clipboard mechanism. The clipboard is almost always used for a one-time response to a user command, such as choosing the Paste command from a menu. DDE is also usually initiated by a user command, but it often continues to function without further user interaction.

Three types of data exchange are possible with DDE:

• Cold link. The exchange is a one-time data transfer, like the clipboard.

• Warm link. A server notifies the client when data changes, and the client must then request new data.

• Hot link. A server sends data updates to the client when data changes.

DDE exchanges can occur between applications running on the same computer or on different computers on a network.

Key Point Most major Windows-based applications support DDE. Like the clipboard, DDE support enables an application to exchange data in a variety of standard formats with other Windows-based applications that support DDE. A developer can also define custom DDE data formats for special-purpose IPC between applications with more tightly coupled communications requirements. For more information, see Dynamic Data Exchange and Dynamic Data Exchange Management Library.

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