ArcGIS Engine Developer Guide

C++ APPLICATION PROGRAMMING INTERFACE
C++ API versus Visual C++ API: Do not confuse
the C++ API with the Visual C++ COM API. If
developing only on Windows, the Visual C++
COM API has advantages over the pure C++ API.
The C++ API is primarily aimed at UNIX and
cross-platform development.
C++ is an object-oriented programming language that evolved in the mid-1980s
from its predecessor, C. C++ is endowed with many features that give the language
an unrivaled expressive power, such as object orientation with inheritance,
operator overloading, virtual functions, templates, and a library of useful and
often necessary functions called the Standard Template Library (STL). The C++
language has been standardized by the International Organization for Standardization
(ISO) and several influential national standards organizations.
Developers may consider using the ArcGIS C++ API, as opposed to one of the
other APIs, for the following reasons:
• Execution speed—C++ code typically executes faster than the equivalent
Java, Visual Basic, C#, and VB.NET code.
• Cross-platform compatibility—Visual Basic, Visual C++, VB.NET, and C# are
currently used primarily on the Windows platform. C++ and Java are inherently
more cross-platform.
• Prior familiarity—If you already have a good deal of experience using the
language, then C++ is a logical choice.
This section is intended to serve two main purposes:
1. To familiarize you with general C++ coding style and debugging.
2. To provide an introduction to the ArcGIS C++ API, detailing specific usage
requirements and recommendations for working with the ArcObjects programming
platform.
C++ DEVELOPMENT TECHNIQUES
Smart types
Smart types are objects that behave like types. They are C++ class implementations
that encapsulate a data type, wrapping it with operators and functions that
make working with the underlying type easier and less error prone. When these
smart types encapsulate an interface pointer, they are referred to as smart pointers.
Smart pointers work with the IUnknown interface to ensure that resource allocation
and deallocation are correctly managed. They accomplish this by various
functions, construct and destruct methods, and overloaded operators.
Smart types can make the task of working with COM interfaces and data types
easier, since many of the API calls are moved into a class implementation; however,
they must be used with caution and never without a clear understanding of
how they are interacting with the encapsulated data type.
The smart types supplied with the C++ API consist of:
• _com_ptr_t—This class encapsulates a COM interface pointer, creating a smart
pointer.
• CComBSTR—This class encapsulates the BSTR data type.
• CComVariant—This class encapsulates the VARIANT data type.
To define a smart pointer for an interface, you can use the macro
_COM_SMARTPTR_TYPEDEF like this:
_COM_SMARTPTR_TYPEDEF(IFoo, __uuidof(IFoo));
Chapter 4 • Developer environments • 197