Consuming C#(dll) functions in a C/C++ project

Question

I need to call/reuse some functions I have in a DLL, developed in C#, within a project done in C.

I already looked for some things and what I managed to make it work was this project: http://support.microsoft.com/kb/828736

This article, step by step, describes how to call a DLL in native C++ . It works cool.

My problem is that this process uses Windows registry and .tlb. file generation.This is causing me a lot of problem as when I make any changes to my DLL, the program in C stops working, even recompiling everything.

So looking I found this other method: http://code.msdn.microsoft.com/windowsdesktop/Consuming-C-Library-in-937458e5

It explains how to consume a C# library in C/C++ without the use of export and import . tlb (which would give me the least headache).

I believe this second method is more efficient and has a much better interface.

The problem is that this second method is much more complicated and I don’t have a very large domain in C/C++. I wonder if anyone’s been through this problem and could give me a hand.

Answer 1

I already had to do this, and I used a slightly different approach (I tested this procedure in Visual Studio 2012 and 2013).

For the test, I created a DLL in C#, called Bibliotecacsharp.dll, with the following class and namespace:

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

namespace BibliotecaCSharp
{
    public class Teste
    {
        public int Soma(int a, int b)
        {
            return a + b;
        }
    }
}

Now, on the C++ side, on another project, to run a code from a library in . Net (be C#, VB etc), the C++ project must be configured to support CLR, as shown in the figure:

Once the project is configured, it is necessary to import the necessary libraries, which is done inside the file stdafx.h of your project in C++, simply add these lines to it:

//Includes e bibliotecas específicas do runtime para .Net
#include <mscoree.h>
#include <vcclr.h>
#pragma comment(lib, "mscoree.lib")

From now on, it is possible to instantiate classes written in C#, or VB.Net directly from within the C code++.

This example project in C++ is a simple console application with only one cpp file, but serves to demonstrate the technique:

#include "stdafx.h"

//Em todos os arquivos que forem acessar a classe, deve-se
//importar as bibliotecas e namespaces
#using <mscorlib.dll>
#using "<CAMINHO DA DLL EM C#>\BibliotecaCSharp.dll"

using namespace System;
using namespace BibliotecaCSharp;

int SomaCSharp(int a, int b)
{
    //Cria uma instância da classe desejada
    Teste^ t = gcnew Teste();

    return t->Soma(a, b);
}

int _tmain(int argc, _TCHAR* argv[])
{
    int s = SomaCSharp(1, 2);

    _tprintf(TEXT("Soma em C#: %d\n"), s);

    return 0;
}

However, the way it is, the C++ code will give error during execution, because the #using "<CAMINHO DA DLL EM C#>\BibliotecaCSharp.dll" is only for the compiler to locate the library, and nay for the program to locate the library when running.

To this end, I always copy the dll in C# to the same folder as the C++ executable, as shown in the figure below:

It would be possible to copy to another folder as long as it is in PATH system, but I find the solution of using the same folder simpler.

Just out of curiosity, this copy can be automated through Post-build Event command line, as the figure shows:

Answer 2

To prevent changes to your DLL written in C# from having an effect on your C++ program, preventing it from working properly, try to fix the global identifier of your module using the instructions in this link.

Behold:

// 
// declare FilgraphManager as a COM coclass 
// 
[ComImport, Guid("E436EBB3-524F-11CE-9F53-0020AF0BA770")] 
class FilgraphManager
{ 
}

Public interface names should not be changed either.