An ATL Primer

Abstract

In previous chapters of this book we saw how to create Windows DLLs with C++. We also saw a sample application of how to integrate DLLs written in C++ with applications written in Visual Basic. This ability to encapsulate functions into DLLs and use them from Visual Basic is very powerful indeed, and in many cases, the best solution to a programming problem. However, the current state (and foreseeable future) of the Microsoft world, and therefore the Visual Basic world, is the Component Object Model (COM). As evidence of this, the Windows 2000 operating system has started to transition some of its application program interface (API) from a set of functions exported from DLLs to a set of COM objects exposing the same functionality. In this chapter and the next, we learn how to use the Active Template Library (ATL) to create COM objects in C++, which can be used from Visual Basic. I will also cover the basic concepts of COM ideology and implementation.