ArcGIS Engine Developer Guide

VISUAL C++
There are many enhancements to ATL in VC7.
Some of the relevant changes are covered in the
section ‘ATL in Visual C++ .NET’ later in this
chapter.
Developing in Visual C++ is a large and complex subject, as it provides a much
lower level of interaction with the underlying Windows APIs and COM APIs
when compared to other development environments.
While this can be a hindrance for rapid application development, it is the most
flexible approach. A number of design patterns, such as COM aggregation and
singletons, that are possible in Visual C++ are not possible in Visual Basic 6. By
using standard class libraries, such as ATL, the complex COM plumbing code can
be hidden. However, it is still important to have a thorough understanding of the
underlying ATL COM implementation.
The documentation in this section is based on Microsoft Visual C++ version 6
and provides some guidance for ArcGIS development in this environment. With
the release of Visual Studio C++ .NET (also referred to as VC7), many new
enhancements are available to the C++ developer. While VC7 can work with the
managed .NET environment and it is possible to work with the ArcGIS .NET
API, this will only add overhead to access the underlying ArcGIS COM objects.
So for the purposes of ArcGIS development in VC7, it is recommended to work
the “traditional” way—that is, directly with the ArcGIS COM interfaces and
objects.
With the addition of the Visual C# .NET language, it is worth considering
porting Visual C++ code to this environment and using the ArcGIS .NET API.
The syntax of C# is not unlike C++, but the resulting code is generally simpler
and more consistent.
This section is intended to serve two main purposes:
• To familiarize you with general Visual C++ coding style and debugging, beginning
with a discussion on ATL
• To detail specific usage requirements and recommendations for working with
the ArcObjects programming platform in Visual C++
WORKING WITH ATL
This section cannot cover all the topics that a developer working with ATL
should know to be effective, but it will serve as an introduction to ATL. ATL
helps you implement COM objects and saves typing, but it does not excuse you
from knowing C++ and how to develop COM objects.
ATL is the recommended framework for implementing COM objects. The ATL
code can be combined with Microsoft Foundation Class Library (MFC) code,
which provides more support for writing applications. An alternative to MFC is
the Windows Template Library (WTL), which is based on the ATL template
methodology and provides many wrappers for window classes and other application
support for ATL. WTL is available for download from Microsoft; at the time
of writing, version 7.1 is the latest and can be used with Visual C++ version 6
and Visual C++ .NET.
ATL in brief
ATL is a set of C++ template classes designed to be small, fast, and extensible,
based loosely on the Standard Template Library (STL). STL provides generic
template classes for C++ objects, such as vectors, stacks, and queues. ATL also
Chapter 4 • Developer environments • 99