Calling unmanaged C code from managed C++ wrapper

[beaute]

Hello. I have a problem and I would love it if I could get some insight on it.
I have read the forums with many answers about the subject, but I'm still having problems so I'm writing here. Basically I was following this guide which is for creating Managed Wrapper from a static library LIB. I thought, static, dynamic, how different could it be.

I have a C program that allows me to do some functions, for simplicity, I am now only using a simple addition function; but the real thing I ultimately want to do is far more complex. For now I just want this simple thing to work.

I'm using MS Visual Studio 2010. I created a Blank Solution with the following three projects:

• AdditionDLL
• Wrapper
• MainCode

AdditionDLL project is a simple C program that has only one function which is to add two numbers together. It is exported as DLL. The code is as follows:

// AdditionClass.c
#include "AdditionClass"
#include <stdio.h>

#pragma once
double Add(double x, double y){
	return x+y;
}

// AdditionClass.h
#pragma once 
static double Add(double x, double y);

This compiles fine and the DLL is created.

Now the Wrapper project is a managed C++/CLR application that is supposed to use the Add function from the AdditionDLL.dll. So I created the project as C++/CLR and change the properties to depend on the dll and also for the linker. Moreover, I have added the AdditionDLL as a reference. Here is the content of the files:

//ClrWrapper.cpp
#include "stdafx.h"
#include "ClrWrapper.h"

using namespace ClrWrapper;

extern "C" __declspec(dllimport)double Add(double x, double y);

//ClrWrapper.h
using namespace System;

namespace ClrWrapper{
	public ref class AdditionClass{
	public:
		double Add(double x, double y);
	};
}

This doesn't compile. It gives me error LNK1107 invalid or corrupt file cannot read at 0x2F0
I know I have a lot of mistakes because I'm trying to make things communicate which shouldn't be communicating. I'd appreciate any help.

The last project is just the C# code to use the Wrapper. I haven't worked on that yet because my wrapper still doesn't work.

[Ancient Dragon]

This works. First you have to export the functions in the DLL that you want to expose to the application program. Here I defined a macro named ADDITIONCLASSAPI so that the same *.h file can be used in both the DLL and application program without change. VC++ 2010 (and earlier versions) define _USRDLL when compiling a DLL project,

// AdditionClass.h
#pragma once 
#ifdef _USRDLL
#define  ADDITIONCLASSAPI __declspec(dllexport)
#else
#define ADDITIONCLASSAPI __declspec(dllimport)
#endif
#ifdef __cplusplus
extern "C" {
#endif
ADDITIONCLASSAPI double Add(double x, double y);
#ifdef __cplusplus
}
#endif

// AdditionDLL.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"

// AdditionClass.c
#include "AdditionClass.H"
#include <stdio.h>

#pragma once
#ifdef __cplusplus
extern "C" {
#endif
ADDITIONCLASSAPI double Add(double x, double y){
	return x+y;
}
#ifdef __cplusplus
}
#endif

Then the C++/CLI program. Make sure this program links with AdditionClass.lib

#include "stdafx.h"
#pragma comment(lib,"AdditionDLL.lib")
using namespace System;
#include "AdditionClass.h"
namespace ClrWrapper{
	public ref class AdditionClass{
	public:
		double Add(double x, double y) { return ::Add(x,y);}
	};
}
int main(array<System::String ^> ^args)
{
	ClrWrapper::AdditionClass w;
	double n = w.Add(1.0, 2.0);
    Console::WriteLine(n);
	Console::Read();
    return 0;
}