Any CPU not available in C++/C# solution

Question

I have a solution that contains C# and managed C++ projects. It compiles in the solution platform x64 and x86. Since it is managed C++ I wanted to create a 'Any CPU' solution and get rid of the old ones.

I changed the C++ project linker settings to Force Safe IL Image for both x64 and x86.

Next, using the Configuration Manager, I created a new solution platform called 'Any CPU'. Next I added a project platform also called 'Any CPU'.

I proceeded to set all the C# projects to 'Any CPU', but for the C++ I can't do that. The project platform 'Any CPU' is not in the drop down, and there is also no option 'New...'.

VS is adement about it, so I kept it like it was and started a build. To my surprise the result DLL (from the C++ project) was MSIL even though the platform for C++ was x64. Same happens when compiling x32, the resulting DLL is in MSIL.

What gives? Why can't I set the C++ project to 'Any CPU'?

Answer 1

As far as I know, you cannot create an "AnyCPU" project type in Visual Studio for a C++/CLI project. However, you can configure your C++/CLI project (under the "Win32" project type) so that it compiles as pure, safe MSIL, without a target platform. Doing so will allow your C++/CLI DLL assembly to be used with an "AnyCPU" C# project. I.e. it's effectively "AnyCPU", even though that's not its actual name in the Configuration Manager.

In the "C/C++" project settings:

• Common Language RunTime Support: Safe MSIL Common Language RunTime Support (/clr:safe)

In the "Linker" project settings:

• CLR Image Type: just make sure this isn't set explicitly to IJW or PURE

Notes:

• By using the "safe" project type, a few of the compiler and linker options which appear to affect platform type will be ignored. I.e. you don't have to go through and set everything to a non-specific platform type. Just the above. But you may set the other options to something appropriate, if it makes you feel better. :)
• "Safe" will prevent the use of pointers. If this is an important issue, it is apparently possible to do albeit with a more complicated process. See Creating a pure MSIL assembly from a C++/CLI project? for details.
• Don't forget that by default, Visual Studio will create C# projects that even though they are "AnyCPU" and even though they are executed on a 64-bit OS, will start up as a 32-bit process. This can hide platform-mismatch issues, if a dependency is x86 instead of pure/safe MSIL as intended. Just something be aware of (you can control this by unchecking the "Prefer 32-bit" option in the C# project's "Build" project properties page).

Answer 2

In order for the C++ functionality to be consumed by a C# dll, the C++ project must produce both x86 and x64 versions of the dll. It is not possible to reference just a x86 or a x64 dll from a C# dll compiled with the AnyCPU setting.

The trick to getting the AnyCPU dll to play with the C++ dll, is at runtime make sure the assembly cannot load the C++ dll and then subscribe to the AppDomain AssemblyResolve event. When the assembly tries to load the dll and fails, then your code has the opportunity to determine which dll needs to be loaded.

Subscribing to the event looks something like this:

System.AppDomain.CurrentDomain.AssemblyResolve += Resolver;

Event handler looks something like this:

System.Reflection.Assembly Resolver(object sender, System.ResolveEventArgs args)
{
     string assembly_dll = new AssemblyName(args.Name).Name + ".dll";
     string assembly_directory = "Parent directory of the C++ dlls";

     Assembly assembly = null;
     if(Environment.Is64BitProcess)
     {
            assembly = Assembly.LoadFile(assembly_directory + @"\x64\" + assembly_dll);
     }
     else
     {
            assembly = Assembly.LoadFile(assembly_directory + @"\x86\" + assembly_dll);
     }
     return assembly;
}

I have created a simple project demonstrating how to access C++ functionality from an AnyCPU dll.

https://github.com/kevin-marshall/Managed.AnyCPU