C++ written dll and C# call

Question

After a long reading time I didn't get the dll working...
I tried so much different ways but no way worked..

I did the following things: (IDE: VS2013Ultimate)

I added a clean c++ project. There I added 1 header file [header.h]:

#pragma once

class myClass{
public:
    myClass(double varx, double vary);
    double sumxy();
private:
    double x;
    double y;
};

I added a body.cpp file:

#pragma once
#include "header.h"

myClass::myClass(double varx, double vary){
    x = varx;
    y = vary;
}

double myClass::sumxy(){
    return x + y;
}

That's all the code I would need. I only want a working example code.

I added one class [main.cpp]:

#include "header.h"  
#include "body.cpp"  

extern "C" __declspec(dllexport) double sumxy(double var_x, double var_y){
    myClass MC(var_x, var_y);

    return MC.sumxy();
}

After this I compiled this dll and I got it without any compile errors. `I copied it to the debug folder of the c# Console Application

C# Console Application:

using System.Runtime.InteropServices;
//all using directories

namespace Klassen_Tester {
    class Program {
        [DllImport("CppClassDll.dll")]
        public static extern double sumxy(double var_x, double var_y);

        static void Main(string[] args) {
            Console.WriteLine(sumxy(3, 5).ToString());

            Console.ReadLine();
        } 
    }
}

Please help me. Don't know what to do.. And sorry for my bad english.

Edit: There is an error: System.DllNotFoundException in Klassen_Tester.exe. DLL "CppClassDll.dll" could not be found. HRESULT: 0x8007007E) could not be load.

First of all, **never** use absolute paths in a `DllImport` attribute. Put `CppClassDll.dll` in the same directory than the C# console exe, and use `[DllImport("CppClassDll.dll")]`. Same thing about `#include`. The isue is that `\U` for instance in a string gets transleted to `U` (the backspace is the escaping character and is ignored in front of a character that does not need escaping) — Lucas Trzesniewski, Aug 20 '15 at 19:44
Yeah i did this before... But i didnt work also.. so i searched other examples.. this is the last one i found.. — Leorus, Aug 20 '15 at 19:45
I did it all in one Project (c++ side) then i compiled it and copied into the debug path of c# project and then i changed the path of dll to the only string and then i started the C# project again and it says: "System.DllNotFoundException" Couldnt load dll — Leorus, Aug 20 '15 at 19:49
It could be that it is required.. I dont know, thats why i am asking.. Its the first dll i am writing.. — Leorus, Aug 20 '15 at 19:55
Is your C++ library [manifested](http://stackoverflow.com/questions/10774250/dllnotfoundexception-with-hresult-0x8007007e-when-loading-64-bit-dll#comment14010912_10774451) @Leorus? — GSerg, Aug 20 '15 at 20:00
If you click that link and read the next comment, it asks just that, and then the next comment answers it. — GSerg, Aug 20 '15 at 20:04
Yes, I mean that. So if it's not the manifest, then use ProcMon to see exactly what is not found, [as suggested](http://stackoverflow.com/a/10774451/11683). — GSerg, Aug 20 '15 at 20:08
Start it, provide a condition that matches your program's process, run your program, find relevant errors in the huge list procmon will generate (most likely will be related to some flavour of CreateFile). — GSerg, Aug 20 '15 at 20:21

score 0 · Answer 1 · answered Aug 20 '15 at 21:36

You might consider using an interop between C++ and C# so you don't have to mess with pinvoke. I'm not saying pinvoke is bad but interops are nice.

You are going to want to write a CLR wrapper to act as an intermediary between the managed and unmanaged code. It looks like you have the C# and C++ mostly written so I'll describe the CLR portion.

Create a CLR project in Visual Studio
Add your native C++ project as a reference
Write your wrapper
Add reference to CLR project from C# project
Call CLR wrapper

Create a class with your C++ signatures likes this:

namespace YourWrapper
{

    public ref class WrappedFunction
    {

        public:

            // Adjust according to your c++ class and function
            double sumxy(double a, double b) {
                return myClass::sumxy(a, b);
            }       
    };

}

For a full example, see my project https://github.com/corytodd/interop-example:

C++ written dll and C# call

1 Answers1