Learning DCOM

Chapter 7. Using COM Objects

In this chapter:

• Simple Client

• The COleDispatchDriver Technique

• The #import Technique

• The Manual Technique

• The Reusable echnique

• Review

You built an OCRServer component in the last chapter, but you have not built a client to use the IOcrProcessor and ISpell interfaces exposed by OCRServer’s COM object. In this chapter, we’ll discuss several techniques for using the services exposed by a distributed component. Specifically, we will discuss four different communication techniques to use with distributed components using C++. These techniques, for lack of better terms, include:

• The COleDispatchDriver technique

• The #import technique

• The manual technique

• The reusable technique

These techniques can be used to take advantage of the functionality exposed by typical distributed components. There are advantages and disadvantages in each of these methods, and we’ll explore them along the way.

In this chapter, we will build a simple MFC client that will use the published services of the OCRServer component developed in the previous chapter. Before you begin, you must register OCRServer either as a service or as a local server on your machine, which requires that you have administrator privileges to the machine that houses OCRServer. You must perform this registration because COM looks in the registry for information regarding this component; see the end of the previous chapter for details on registering this component.