VS2010中的C ++运行针对.NET 4.5的托管C＃DLL

Question

I have a C++ project, created in Visual Studio 2010, which needs to execute code from a C# DLL. I have done so using the

#import "pathname\filename.tlb" raw_interfaces_only

directive, as well as the CoInitialize(NULL) and CoUninitialize() COM calls.

The C# DLL was compiled in VS2012, and targeted .NET 4.5.

I was able to compile and run the project, and it seemed as though everything was fine, but we were noticing differences in some function calls. This was verified by loading the exact same C++ project into VS 2012, turning on /clr in Configuration Properties, and changing the Targeted Framework (of the C++ project) to v4.5 by modifying the .vcxproj file in Notepad.

So, I guess my questions are:

1. Why does a C++ project need to target a .NET framework? Shouldn't the C# DLL be able to handle that by itself? (Answered by Hans Passant)

2. Why is it possible to run a C#.NET v4.5 DLL through C++ with /clr off, and not have any warnings that it might not work? (Answered by Hans Passant)

3. Why do I even get results back from the function call? How is it possible that the C# DLL "works" (returns coherent results) at all? Why does it return different values when targeting .NET v4.0?

4. Is it possible to use the C# DLL from the C++ code, while still using VS 2010? Or do I need to switch the project to VS 2012?

Thanks in advance.

Answer 1

A native C++ project does not target the .NET Framework at all. The project creation wizard is a bit clumsy, it does not hide the combobox when you create the C++ project.

What framework version the C# DLL needs is established when you register it. Either done automatically when you tick the "Register for COM interop" build setting or explicitly by running Regasm.exe.

That native C++ code can call C# code without trouble is just a goody you get from using COM. Whose basic purpose is to provide the contracts and the glue to allow one language to call code written in another. The CLR has very good COM support and makes it look very easy. That's not the case for C++, writing COM client code is generally unpleasant due to the verbosity and it is pretty easy to make mistakes. Using raw_interfaces_only is a mistake, you don't get the benefit of memory management with smart pointers and error handling with exceptions.