Targeting C++/CLR v2.0 with Visual Studio 2010

I just spent far too many hours recovering from trying to change the target .Net Framework version for a C++/CLR project in Visual Studio 20010 (final release.) I hope to save someone else the same frustation. If you don't need the features in .Net 4.0, there's a big advantage to targeting the old version since it is much more likely that your customers will have the old version installed.

If you go into the Framework and References page for a C++/CLR project in Visual Studio 2010, you will see that the Platform droplist is grayed out. There's nothing you can do to ungray it, so don't bother trying.

Underneath it says, "Targeted framework: .NETFramework, Version=4.0" There's no button you can click to change that. If you RTMF, the documentation says that, "The IDE does not support modifying the targeted framework, but you can change it manually." So that's what I tried to do. I went into the vcxproj file, changed the header to say ToolsVersion="2.0" and reloaded the project. Big mistake. The updated project file wouldn't load. I reverted back to the original file from source control and that wouldn't load either.

The first error I had to fix was:

The imported project "C:\Microsoft.Cpp.Default.props" was not found. Confirm that the path in the <Import> declaration is correct, and that the file exists on disk.

This turned out to be relatively easy to solve. I went into the vcxproj file and did a "Replace All" changing UserRootDir to VCTargetsPath.

The second error was something about ClCompile and not finding AssemblyInfo.cpp. I'm still not entirely clear what caused this because now I can't reproduce the problem. In the end, I removed the project from the solution, closed the solution, closed Visual Studio, deleted the .sdf file, deleted all of the build directories (Debug, Release, etc.), deleted the ipch directory, restarted Visual Studio, added the project back into the solution, and it worked.

None of which got me any closer to solving the original problem.

I created a new C++/CLR project from scratch, which pointed me at the answer. The project file I was using had been created by the Upgrade Wizard in Visual Studio 2010 and it turns out that an important line was left out. Underneath these two lines:

<PropertyGroup Label="Globals">
   <ProjectGuid>{96FD1FEF-8A07-44E6-9CC1-
D4284218B186}</ProjectGuid>

there should be another line that says:

   <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>

Change it from v4.0 to v2.0 and everything will magically switch to v2.0. The value v3.5 is also supported. There's some discussion of this at http://blogs.msdn.com/vcblog/archive/2010/03/02/visual-studio-2010-c-project-upgrade-guide.aspx halfway down under Known issues for conversion in VS2010.

Note that using v2.0 forces Visual Studio to use the Visual Studio 2008 compiler. Visual Studio 2010 can only compile v4.0 code.

Update 6/18/2010: To debug your code, you may have to explicitly tell Visual Studio 2010 that the .Net 2.0 CLR should be used. I ran into this when my EXE was native and my DLL was C++/CLR. Create a file named .exe.config and put the following information in the file:

<configuration>
    <startup>
        <supportedRuntime version="v2.0.50727"/>
    </startup>
</configuration>

 
More information can be found in this article on the Visual Studio Debugger Team Blog. Note that their sample did not work for me under Windows Vista until I removed the line that said:
 
<?xml version ="1.0"?>