The Active Template Library

The Active Template Library (ATL) is a collection of C++ templates included in Microsoft® Visual C++® version 5.0. This template library is intended specifically to facilitate the creation of Component Object Model (COM) objects.

Although you can create a pipeline component using any build environment that supports the creation of free-threaded COM servers, the use of ATL is recommended for the following reasons:

• υSmall, fast code. COM components created using ATL are smaller and faster that other approaches to component creation, including approaches supported by Visual C++. Although you can easily create COM components using the Microsoft® Foundation Classes (MFC) library, you incur significant memory overhead that is occasioned by using a large class library. This overhead is particularly undesirable for shared server components.
• υGenerous user interface support. The use of ATL makes it possible for you to create pipeline components using features built into the Visual C++ 5.0 user interface. This approach significantly reduces the learning curve that attends learning certain COM implementation details, and also reduces the amount of code you have to write. For example, when you use ATL, the Interface Definition Language (IDL) files for your component’s interfaces are created for you based on the method and property definitions that you specify, and adding new objects to a project can be performed with two or three mouse clicks. This saves you the work of hand-coding modifications to your component's IDL file.

For information about the Active Template Library, see the ATL Tutorial, which is included with Visual C++.