Trying to call a C++ DLL in C# (Repost from Visual C++ Forum)

[moxman99]

Hello All,

I have reposted this from the Visual C++ forum since it could also be solved in this C#Forum.

I am trying to call a C++ DLL in C#.

I have read numerous forums, however I cannot seem to get a simple math function to be called from within my C#.

One thing I have to mention is my DLL I am calling is made to call another DLL. It works fine when I created a console application in C++ and then called the secondary DLL, which in return called the methods from the first DLL. My secondary DLL being called from the C# is MyExecRefsDll.dll. The DLL in which it calls is MathFuncsDll.dll. All of the C++ code was taken from a tutorial here:http://msdn.microsoft.com/en-us/library/ms235636(v=vs.100).aspx

Here is the header and cpp code for MyExecRefsDll.dll:

// MyExecRefsDll.h

#pragma once
extern "C"{



#ifdef MYEXECREFSDll_EXPORTS
#define MYEXECREFSDll_API __declspec(dllexport)
#else
#define MYEXECREFSDll_API __declspec(dllimport)
#endif


namespace MyExecFuncsNS
{

class MyDoMathCall
{
public:
static MYEXECREFSDll_API int DoMath();
};
}}

And here is the cpp:

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

#include "stdafx.h"

#include <iostream>

#include "MathFuncsDll.h"
#include "MyExecRefsDll.h"

using namespace std;

namespace MyExecFuncsNS
{
int MyDoMathCall:oMath()
{
double a = 7.4;
int b = 99;

cout << "a + b = " <<
MathFuncs::MyMathFuncs::Add(a, b) << endl;
cout << "a - b = " <<
MathFuncs::MyMathFuncs::Subtract(a, b) << endl;
cout << "a * b = " <<
MathFuncs::MyMathFuncs::Multiply(a, b) << endl;
cout << "a / b = " <<
MathFuncs::MyMathFuncs:ivide(a, b) << endl;

try
{
cout << "a / 0 = " <<
MathFuncs::MyMathFuncs:ivide(a, 0) << endl;
}
catch (const invalid_argument &e)
{
cout << "Caught exception: " << e.what() << endl;
}

return 0;
}

}

Now here is the MathFuncsDll.h code:

// MathFuncsDll.h
#pragma once

#ifdef MATHFUNCSDLL_EXPORTS
#define MATHFUNCSDLL_API __declspec(dllexport)
#else
#define MATHFUNCSDLL_API __declspec(dllimport)
#endif


namespace MathFuncs
{
// This class is exported from the MathFuncsDll.dll
class MyMathFuncs
{
public:
// Returns a + b
static MATHFUNCSDLL_API double Add(double a, double b);

// Returns a - b
static MATHFUNCSDLL_API double Subtract(double a, double b);

// Returns a * b
static MATHFUNCSDLL_API double Multiply(double a, double b);

// Returns a / b
// Throws const std::invalid_argument& if b is 0
static MATHFUNCSDLL_API double Divide(double a, double b);
};
}

And the respective cpp file:

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

#include "stdafx.h"
#include "MathFuncsDll.h"
#include <stdexcept>

using namespace std;

namespace MathFuncs
{
double MyMathFuncs::Add(double a, double b)
{
return a + b;
}

double MyMathFuncs::Subtract(double a, double b)
{
return a - b;
}

double MyMathFuncs::Multiply(double a, double b)
{
return a * b;
}

double MyMathFuncs:ivide(double a, double b)
{
if (b == 0)
{
throw invalid_argument("b cannot be zero!");
}

return a / b;
}
}


Here is my C# code I am calling the MyExecRefsDll.dll from:

// Marshal.cs
using System;
using System.Runtime.InteropServices;

class PlatformInvokeTest
{

public static class DllHelper
{

[DllImport(@"c:\Users\tester\Documents\Visual Studio 2010\Projects\DynamicLibrary\Debug\MyExecRefsDll.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "DoMath()")]

public static extern int DoMath();
}


static void Main(string[] args)
{

try
{
DllHelper.DoMath();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}


}
}

Now the error I receieve is when it cannot find the EntryPoint name. I receieve this error

A first chance exception of type System.EntryPointNotFoundException occurred in Example Project1.exe

So I have read many forums and I see that I need to include and extern "c" in my header files for the call however I am very confused for how to implement and why this is needed. I undertstand I am linking the DLL to the C# language but am having the hardest time.

I am using Microsoft Visual C# and C++ Express 2010.

Any help would be greatly appreciated.

Kind Regards.

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