Question

I’m trying to make my first c# dll.
I want to be able to call it’s methods/functions from ruby with win32API.
I have made this dll:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ClassLibrary1
{
    public class Class1
    {

        public int PropA = 10;

        public void Multiply(Int32 myFactor)
        {
            PropA *= myFactor;

        }
    }
}

I compiled it with Visual Studio 2010 and got my ClassLibrary1.dll file.

Now for the ruby part i tried this:

f = "c:/path_to_file/ClassLibrary1.dll"
mult = Win32API.new(f,"Multiply",["I"],"I")

But, i get the following error:

Error: #<RuntimeError: (eval):0:in `initialize': GetProcAddress: Multiply or MultiplyA

To be honest, I never created a dll, nor do I have experience with c#. I just wanted to get started. I have used many dll’s with Ruby via win32API before (user32 mostly).

I guess my dll is not ok?

Regards,

Answer 1

To consume functions from DLLs as done in a Win32 context, these functions need to be export-visible from the DLL. These functions are usually flagged with dllexport and will show up in the export table of a DLL. You can verify that user32 and other Win32 DLLs do this by using a utility such as dumpbin (MSDN).

dllexport, dllimport @ MSDN

Unfortunately, .NET doesn’t have immediate support for making functions export-visible, only for bringing in such functions via the DllImport (MSDN) Attribute.

COM is the easiest way to consume code written within .NET from a non-.NET environment, but if you must use the lower level bindings, you can make an intermediate DLL in C, C++/CLI, or any other language and framework combination that can write export headers to a dll, to call your .NET code.

Also, A few articles exist on making this happen via post-compilation automation or other workarounds, here are a few for your reference.

How to Automate Exporting .NET Function to Unmanaged Programs @ CodeProject

Unmanaged Exports @ Google Sites

DllExport – Provides C-style exports for pure .NET assemblies