How do I add a reference to an unmanaged C++ project called by a C# project?

Question

One solution (the.sln)

One C++ project (mycppproject.vcxproj in 2010or mycppproject.vcproj in 2008) which compiles a native DLL exporting some function(s). In debug this builds c:\output\Debug\mycppproject_d.dll and in release this builds c:\output\Release\mycppproject.dll.

One C# console application (mycsharpconsole.csproj) containing PInvoke calls into the DLL.

All compiles fine.

When I build, I would like to be able to add a reference from the csharp project to the cpp DLL project so that it can copy the appropriate file from the appropriate directory into the \bin\Debug directory the csharp project is built into.

This should be possible, since the IDE knows everything there is to know about where the DLL gets built, and where the C# application gets built.

In Visual Studio 2010:

I've tried "Dependencies..." on the csharp project and adding a dependency on mycppproject, but that has no effect.

I've tried "Add Reference..." on the csharp project and adding a reference to the cpp project, but I get a warning message 'The Target Framework version for the project "mycppproject" is higher than the current project Target Framework version. Would you like to add this reference to your project anyway?' (Yes/No/Cancel).

Clicking "Yes" produces the error message "A reference to mycppproject" could not be added."

Solution 1

Visual Studio doesn't support referencing an unmanaged C++ project from a managed C# one, but MSBuild supports referencing any project from any other project.

You can manually add a reference to your project by editing the .csproj file by hand. In the file, find your existing set of ProjectReference elements (or add a new ItemGroup if you don't have one) and add the following reference:

<ProjectReference Include="..\mycpproject.csproj">
  <Project>{b402782f-de0a-41fa-b364-60612a786fb2}</Project>
  <Name>mycppproject</Name>
  <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
  <OutputItemType>Content</OutputItemType>
  <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</ProjectReference>

When you perform the build, the reference will cause MSBuild to build the referenced project first. The ReferenceOutputAssembly value tells MSBuild not to copy the output assembly of the build (since the C++ project does not produce one), but the OutputItemType and CopyToOutputDirectory values instruct it to copy the output content to the referencing project's output folder.

You will be able to see the reference in Visual Studio, but you can't do much with it there.

This answer is based on a similar problem solved by Kirill Osenkov on his MSDN blog: https://blogs.msdn.microsoft.com/kirillosenkov/2015/04/04/how-to-have-a-project-reference-without-referencing-the-actual-binary/

Solution 2

You cannot add a reference to an unmanaged DLL.

Instead, you should make a post-build task to copy the file.

Alternatively, you can add a link to the unmanaged DLL as a file in the C# project, and set Build Action to None and Copy to Output Directory to Copy If Newer.

Solution 3

I would follow Slaks' second answer...

[...] you can add a link to the unmanaged DLL as a file in the C# project, and set Build Action to None and Copy to Output Directory to Copy If Newer.

... followed by my comment, to differentiate between Debug and Release builds (even if is a little bit "hackish", since it requires you to manually edit the C# project file)

open your C# project's csproj file with a text editor and search for all "YourNativeCppProject.dll" occurrences (without the ".dll" subfix, so if you added pdb files as a link too, you'll find more than one occurrence), and change the Include path using macros, for example: Include="$(SolutionDir)$(ConfigurationName)\YourNativeCppProject.dll

PS: if you look at the properties (F4), VS shows you the Debug's path even if you switch to the Release configuration, but if you compile, you'll see that the dll copied to output is the release version*

Solution 4

Add Rederences only works for .NET assemblies, .net projects in the same solution or for COM components ( for which a manager wrapper will be created anyway... ).

the fact that in your C# code you access the C++ dll with DLLImport does not mean that Visual Studio will know from where to where the external dll should be copied.

Imagine that DLLImport is a runtime option, the path you puth in there is used at runtime to look for the dll, so you have to deploy the c++ dll yourself and make it available for the .net application, usually in the same bin folder.

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Comments

[JoeG]

possible duplicate of Add a Reference from a C# App to a DLL compiled without /clr?

[WaffleSouffle]

Apologies, this does indeed appear to be a duplicate of that question. Failed to find it in my initial search.

[WaffleSouffle]

I hoped it could be set up to copy the unmanaged DLL locally, since that's what Visual Studio does with .NET class library DLLs as standard, and really this is not so very different. Ultimately they get loaded at runtime too.

[WaffleSouffle]

The .NET compilation model is either "in the GAC", or "all in one folder". It would be nice if unmanaged code had support making this easier. Although as you say it's all at runtime and the DLL could come from anywhere, for developers writing modularised libraries, some additional tooling to help manage locations wouldn't go amiss in my opinion.

[Matt Warren]

If I use your 2nd suggestion, will it pick up the new file if the C++ dll gets rebuilt? It seems to make a copy of the file at the time you add it as a link into the project.

[SLaks]

@Matt: Choose Add as Link from the dropdown in the open dialog.

[WaffleSouffle]

This doesn't help for different build configurations like Release and Debug.

[Notoriousxl]

@WaffleSouffle: open your C# project's *.csproj file with a text editor and search for all "YourNativeCppProject.dll" occurrences (if you added *.pdb files as a link, you'll find more than one occurrence), and change the Include path using macros, for example: Include="$(SolutionDir)$(ConfigurationName)\YourNativeCppPro‌​ject.dll" PS: if you look at the properties (F4), VS shows you the Debug's path even if you switch to the Release configuration, but if you compile, you'll see that the dll copied to output is the release version

[WaffleSouffle]

@Notoriousxl That's essentially what I ended up doing: Defined a load of MSBuild properties and targets and used those to drive the location resulting in a $(YourNativeCppProjectDLLPath) property. Note that solution properties are not available if running MSBuild on a .csproj. You should post this as an answer, because MSBuild properties are definitely the way to go, rather than relying purely on the Visual Studio IDE. MSBuild does introduce another level of interesting behaviour though.

[WaffleSouffle]

Nothing hackish about editing the .csproj file in my opinion. More of a requirement.

[Notoriousxl]

@WaffleSouffle "a little unmanaged by Visual Studio and Property Window", so :D

[BTownTKD]

I actually prefer to set the Build Action to "Content." In this way, the dependant DLLs are automatically copied to the output directory of Setup & Deployment projects, 2nd-tier applications (which depend on the library which contains the original DLL dependencies), etc. It just accounts for more use-cases.

[jnm2]

This works really well. The only problem is that the native DLL never gets built when its code changes unless you manually build the C++ project, even with project dependencies correctly set up. Do you have a solution for this?

[Notoriousxl]

@jnm2 no, I'm sorry, but it's strange: I'd expected build problems on the c# project, but if you modify project A, A should build regardless (but anything could be possible, since this is a hack). The only thing that comes to mind (but you probably already checked it): does the native project have the "build" flag checked on Configuration Manager?

[jnm2]

@Notoriousxl It was actually a third project that wasn't updated. More details here. stackoverflow.com/q/34657743/521757

[Gaspode]

I'm seeing it the other way round; building the 'startup' c# project does get the native dll dependent built, BUT it doesn't copy it because the c# project is up to date. I've had this problem with both managed and native plug-in (run time dependency) dlls for ten years how. I do wish MS would improve support for this model of dev. Still hitting it in VS2015 :(

[dlf]

This, IMO, is more idiomatic than using a post-build copy step or inserting a link. (1) Unlike a manual copy, it handles the "transitive" case properly. If A references B references C references D references native.dll, why should I have to tell A to copy native.dll into its output directory? A shouldn't even need to know that native.dll exists. (2) It automatically selects the debug/release/etc. version of the native dll as needed. There is no simple way to get that behavior with a link. It's just a shame VS won't let you set things up this way in the UI.

[dlf]

But unfortunately this approach seems to confuse VS in the case of transitive dependencies (managed A depends on managed B depends on native C)--it will copy the native dll to the final output directory when you do a clean build, but on subsequent builds, it will actively delete it from there. :(

[chtenb]

This isn't working for me. The reference does show up in Visual Studio, but no assemblies/files are copied whatsoever.

[chtenb]

Correction: content files are copied correctly, but newly compiled artifacts are not.