Environment: VC6 SP1, SP2, SP3, NT4 SP4
ATL has no native string class. To manipulate strings, you have several
choices: Standard Template Library (STL), roll-your-own C++ classes, or the
tried-and-true MFC CString class. The problem with CString, though, is that it’s
part of the MFC library. Many developers will include MFC support in their ATL
servers just to get the CString class. However, this defeats ATL’s goal of
producing small, efficient, high-performance servers – and it’s not necessary!!!
Instead, the CString class can be extracted from the MFC source code,
massaged ever so slightly to use ATL macros, and all MFC dependencies removed.
The resulting class can then be used in any ATL server without including MFC! Of course, to extract the MFC CString class, you must locate all the
files that contain the CString source code,
convert MFC macros/methods to ATL equivalents and remove the dependencies on MFC. This is not a difficult task,
just tedious and time consuming.
Since I cannot distribute the extracted CString source code as it would violate the
Microsoft EULA, I have done the next best thing – created a DevStudio macro that
will do the extraction for you based on your licensed copy of the MFC source
code files. The result is two files, a .h and .cpp file that will be placed in
the ATL SRC and INCLUDE directories. You can then add these files to any ATL
project and get all the benefits of the fully functional CString class.
To produce the files, download and open the MFCCStringForATL.DSM macro file.
Find the following lines and modify the path specified by
sDevStudioPath to match the location of your DevStudio source files.
' Replace with your equivalent path to the Dev Studio directory.
dim sDevStudioPath
sDevStudioPath = "C:Program FilesMicrosoft Visual StudioVC98"
Save the MFCCStringForATL.DSM macro file if modifications were made. Next,
load the macro via the Tools | Customize menu, Add-ins and Macro Files tab.
Click browse and locate the MFCCStringForATL.DSM file. Select Open. Select Close
to close the Customize dialog. Next, select Macro from the Tools menu to display
the Macro dialog. Make sure the correct macro file is selected, then select Run.
If the macro is successful, the newly generated files will be placed in the ATL
Src and Include directories. (default location – C:Program FilesMicrosoft Visual StudioVC98ATL)
Testing
To make sure the extracted CString methods work exactly as they do in an MFC
project, I have included an MFC test application that tests the native MFC CString class
and the extracted ATL version. The ATL version is tested via an ATL COM
component. The MFC test application creates an instance of this component and
calls a method which performs the tests and returns the results. The test cases
were taken from the MSDN documentation. Believe it or not, some of
the CString methods fail using the documented test cases. However, the tests
fail in both versions which is the point of the test application – to prove that
the CString class is successfully extracted and performs identically to the MFC
version. If you build the test application and ATL component, make sure that
both of the build configurations are identical (Debug/Debug, Debug Unicode/Debug
Unicode, Release/Release, etc). It is important to test apples to apples.
Otherwise, the test results are meaningless.
Notes
The CString class uses C++ exception handling. Unless you want to modify the
extracted class, your ATL servers must have C++ exception handling enabled. It
is disabled by default.
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