Cover by Rasmus Lerdorf, Peter MacIntyre, Kevin Tatroe

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Interfacing with COM

COM allows you to control other Windows applications. You can send file data to Excel, have it draw a graph, and export the graph as a GIF image. You could also use Word to format the information you receive from a form and then print an invoice as a record. After a brief introduction to COM terminology, this section shows you how to interact with both Word and Excel.

Background

COM is a Remote Procedure Call (RPC) mechanism with a few object-oriented features. It provides a way for the calling program (the controller) to talk to another program (the COM server, or object), regardless of where it resides. If the underlying code is local to the same machine, the technology is COM; if it’s remote, it’s Distributed COM (DCOM). If the underlying code is a DLL, and the code is loaded into the same process space, the COM server is referred to as an in-process, or inproc, server. If the code is a complete application that runs in its own process space, it is known as an out-of-process server, or local server application.

Object Linking and Embedding (OLE) is the overall marketing term for Microsoft’s early technology that allowed one object to embed another object. For instance, you could embed an Excel spreadsheet in a Word document. Developed during the days of Windows 3.1, OLE 1.0 was limited because it used a technology known as Dynamic Data Exchange (DDE) to communicate between programs. DDE wasn’t very powerful, and if you wanted to edit an Excel spreadsheet embedded ...

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