使用Visual Studio 2013将C / C ++ DLL生成并交付到C＃应用程序中

Question

I am a Visual Studio 2013 Newbie who is trying to figure out how to build a C DLL in Visual Studio and then invoke the functions exported by the C lib from within a C# app. I've got everything building, but I cannot figure out the proper way of getting the DLL included with the app build so that it will actually load properly when using [DLLImport()] . I currently get a System.DllNotFoundException when attempting to invoke a function from the library from within my C# class.

I have setup a VS 2013 solution which contains the following projects:

HelloWorldLib.Shared : Shared project that contains the .cpp and .h files for the DLL

HelloWorldLib.Windows : Win 8.1 C++ project that references the shared project and builds the DLL for Win 8.1

MyApp-Win.Windows : C# project for Win 8.1 that wants to make use of the HelloWorldLib.Windows.dll produced by the HelloWorldLib.windows build

I have been looking over many SO questions and answers. For instance, I think my question is similar to this one, which doesn't appear to have been answered in any useful way: Interop, Native DLL and Visual Studio build process

Some of the other answers suggested adding a file reference to the DLL, but how would I do that and keep the proper Debug/Release versions? Given that all of these projects are being built within the same solution, and there are build dependencies between them, it feels like there should be a straightforward way to set this up.

BTW, I am using the shared project setups, as my ultimate goal is to figure out how to get this all working with Xamarin to target iOS, Win, Win Phone, Mac and Android. So that we can use a common C/C++ layer for our high performance requirement code, and the reference it from the UI layers on the various platforms.

Answer 1

This is a pretty straight-forward problem, easy to identify if you look where the built files end up. The C++ build system has a different strategy than the managed build system. It by default writes the build output to the solution directory's Debug directory. Your C# project however builds to its bin\\Debug directory and requires all dependent DLLs to be present there.

So, by default, your C# program can never find the DLL, it is in the wrong directory and Windows doesn't look there. Nor is MSBuild smart enough to discover this by itself, like it can for managed DLLs, it cannot see that you program depends on the C++ DLL.

Two basic ways to work around this:

• Change the C++ project's Output Directory setting
• Write a post-build event for your C# project that uses xcopy.exe to copy the DLL.

Answer 2

Unfortunately things aren't that easy, at least not yet. I was going to have a meeting with Microsoft C++ team but that got postponed, similar functionality you are after was one of the things on my wishlist (building managed C++/CLI wrappers for Xamarin.iOS and Android).

Currently, if you can, the easiest option is to wrap C++ code inside a DLL that exposes C interface. Then build it with XCode and Android NDK. If you can't then the next option is to create Objective-C binding project that wraps the C++ code inside Objective C classes for iOS. For Android either create Java wrapper or use SWIG . Both of these options are cumbersome which is why C API should be the first choice you investigate.

I know it's not the answer you were hoping for but reusing C++ code is way more complicated than reusing C# or even C.