DDE and OLE are both for sharing data between applications. When should you use DDE and when should you use OLE?
DDE is good for exchanging distinct text strings. If all you want to know is the bottom line of a profits spreadsheet, it makes sense to link the cell that contains the bottom line to a Delphi DDE client application. Then you could output the data in an edit box or label. DDE protects the data in the spreadsheet by not allowing the user to activate and edit the spreadsheet from your client application.
OLE is able to exchange more complex information than DDE, such as sounds and documents. Control transfers to the OLE server application when you activate an object in your OLE container, so the user can access all the functionality of the server application from within your container application. The server does all the processing and you don't have to program your container to edit the OLE object. This would be good if you wanted to allow your users to modify the profits spreadsheet from within your application.
The final factor in determining when to use DDE and when to use OLE is the capabilities of the applications involved. Some Windows applications don't support DDE. Some don't support OLE. Other applications can be OLE containers, but can't be OLE servers. For more information, see the documentation for the application with which you want to exchange data.
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