18.1. COM
The component object model (COM) is a framework that allows sharing of executable modules without recompiling. If you have used Windows for any time at all, you are aware of dynamic-link libraries (DLLs), collections of functions a program can load on demand. Many programs can share a DLL. Unfortunately, DLLs that work well with some programming languages don't work at all with others. COM seeks to solve this problem. COM objects are accessible by C++, Visual Basic, PHP, and many other programming languages.
A tutorial on COM is beyond the scope of this text, of course. Microsoft's list of “noteworthy” books about COM is relatively long <http://www.microsoft.com/com/tech/com.asp>. However, you could keep busy just reading the articles ...
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