The Active Template Library (ATL) is a set of template-based C++ classes developed by Microsoft that simplify the programming of Component Object Model (COM) objects. The COM support in Microsoft Visual C++ allows developers to create a variety of COM objects, OLE Automation servers, and ActiveX controls. Patterned after the Standard Template Library (STL), ATL includes an object wizard that sets up primary structure of the objects very quickly with a minimum of hand coding.

Controls for the Internet market could have been made with the Microsoft Foundation Classes, but this market requires controls to be small and compact for downloading over the network from Web servers. MFC applications tend to be large and require support DLLs. ATL allows creating smaller controls without support DLLs, so ATL is in a sense a lightweight alternative to MFC for the COM control environment.

A common use of ATL in ASP (Active Server Pages) is to construct objects that can be called from a script. Whilst limited in certain respects, VBScript is able to call C++ Windows code contained in a COM object.

See also

• ATL Server
• Component Object Model (COM)
• Microsoft Foundation Classes (MFC)
• OLE Automation
• Standard Template Library (STL)
• Windows Template Library (WTL)
• Microsoft Platform SDK

References