If you look at the source code for ATL, you'll find that ATL consists of a collection of header files and C++ source code files. Most of it resides inside the ATLMFC\Include directory that comes with the installation of Microsoft Visual Studio .NET. Here's a rundown on some of the ATL files and what's inside each of them.
This file contains:
ATL's function typedefs
Structure and macro definitions
Smart pointers for managing COM interface pointers
Thread synchronization support classes
Definitions for CComBSTR, CComVariant, threading, and apartment support
Template classes for class object/class factory support
IUnknown implementations
Support for tear-off interfaces
Type information management and support
ATL's IDispatch implementation
COM enumerator templates
Connection point support
These two source code files include support for Unicode conversions.
These two files contain:
The source code for ATL's IDispatch client support and event firing support
CComControlBase
The OLE embedding protocol support for controls
Property page support
AtlIFace.idl (which generates AtlIFace.h) includes an ATL-specific interface named IRegistrar.
AtlImpl.cpp implements such classes as CComBSTR, which is declared in AtlBase.h.
These files provide windowing and user-interface support, including:
A message-mapping mechanism
A windowing class
Dialog support
ATL features a COM component named the Registrar that handles putting appropriate entries into the Registry. The code for implementing this feature is in StatReg.h and StatReg.cpp.
Let's start our excursion into ATL by examining ATL's support for client-side COM development.