create C++ DLL to be used by C# ?

Question

I want to write a native C++ function that I can later access from C#.

Please keep in mind I do not have much experience developing on windows, (mostly unix) and that my only windows compiler is VS2005.

I tried creating a MFC DLL.  I am able to access this from a C++ .net program, but not from a C# program using P/Invoke.  It seems that a plain MFC DLL is not "good enough" for use with DllImport.  Is this correct?

It seems that I have two options:

  1) compile the C++ function as a COM DLL (not sure how to do this from VS2005 - I don't see an option for that).  I see an option for an ActiveX DLL...I hope I don't need to do that.

 2) write a C++ .net wrapper class, create a .net assembly, and use that assembly from C#.

I would prefer option 1...how do I create a DLL that C# can use via [DllImport] ?

Answer 1

I suspect that ActiveX means COM, ActiveX was the initial name for COM.

 

Answer 2

It is a matter of opinion but COM interop in C++ always struck me as a "keep the boss happy" option.  Either write it in straight C++ and use the DllImport attribute or write it in C++/CLI (ref class, "hat" and all that) and create a native .NET assembly.

Answer 3

I would tend to agree.  While you asked for the COM option as a preference, it's really much better to just compile it as C++/CLI code, you need the .NET framework anyhow, and it's much more flexible to work with it that way.

 

Answer 4

hello ,

 just  write one pure win32 dll  . and just pass parameter as void * . it works

remember when u pass string or character values it is 2 byte in c# and in mfc it is 1 byte. U have to do the conversion

 

Answer 5

I have created a simple win32 dll that I can access from C++ in VS2005.

My question was, what do I need to do to access it from C# ?  Simply using P/Invoke does not work.

Another suggestion was just to write a C++ .net dll, and call that from C#.  I will try this, but I have a hard time believing this will be as fast as native code (I am porting some image processing routines from a unix environment).   Once I have created a .net dll from c++, it looks like I need to do these steps:

1. create a "strong name" with the sn utility
2. run gacutil

Is this correct?  I can't simply link against the .net DLL?

Answer 6

Once it's a .NET dll, you just need to add a reference to it in your project.

 

Answer 7

"Simply using P/Invoke does not work".   Why not, what goes wrong?  What is the declaration of the C++ function?

Answer 8

Rick, also take a look at your previous post at http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=472900&SiteID=1

Thanks,

Ayman Shoukry

VC++ Team