How to create dll in C++ for using in C#

Question

I've a little question to ask you.

I have one C++ source and one header files. The C++ file uses windows.h library, makes operations using serial port(basic operations: read(), write() etc.).

What I want to do is, creating a library using these files, and use that library in my C#.Net solution.

What type of library I need to create? How can I do it? After creating library, How can I import it to C# solution?

My best regards.

Code Parts I'm using:

// MathFuncsDll.h

namespace MathFuncs
{
    class MyMathFuncs
    {
    public:
        // Returns a + b
        static __declspec(dllexport) double Add(double a, double b);

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

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

        // Returns a / b
        // Throws DivideByZeroException if b is 0
        static __declspec(dllexport) double Divide(double a, double b);
    };
}

// MathFuncsDll.cpp
// compile with: /EHsc /LD

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

        return a / b;
    }
}

C# import part:

[DllImport("SimpleDll.dll", CallingConvention=CallingConvention.Cdecl)]
public static extern double Add(double a, double b);

static void Main(string[] args)
{
    string a = Add(1.0, 3.0));
}

Answer 1

After several comments, here a try:

C++ Code (DLL), eg. math.cpp, compiled to HighSpeedMath.dll:

extern "C"
{
    __declspec(dllexport) int __stdcall math_add(int a, int b)
    {
        return a + b;
    }
}

C# Code, eg. Program.cs:

namespace HighSpeedMathTest
{
    using System.Runtime.InteropServices;

    class Program
    {
        [DllImport("HighSpeedMath.dll", EntryPoint="math_add", CallingConvention=CallingConvention.StdCall)]
        static extern int Add(int a, int b);

        static void Main(string[] args)
        {
            int result = Add(27, 28);
        }
    }
}

Of course, if the entry point matches already you don't have to specify it. The same with the calling convention.

As mentioned in the comments, the DLL has to provide a C-interface. That means, extern "C", no exceptions, no references etc.

Edit:

If you have a header and a source file for your DLL, it could look like this:

math.hpp

#ifndef MATH_HPP
#define MATH_HPP

extern "C"
{
    __declspec(dllexport) int __stdcall math_add(int a, int b);
}

#endif

math.cpp

#include "math.hpp"

int __stdcall math_add(int a, int b)
{
    return a + b;
}

Answer 2

You need to compile your C++ code into a dynamic link library and do the following in C#:

  class MyClass
  {
  [DllImport("MyDLL.dll")]
  public static extern void MyFunctionFromDll();

        static void Main()
        {
              MyFunctionFromDll();
        }
  }

Answer 3

You may use C# DllImport and Dllexport for DLL Interop walkthrough as a starting point. And here is the Platform Invoke Tutorial

Hope this helps.

Answer 4

In addition to Lichian's offer to compile to a regular DLL and use p/invoke which is probably the simplest way You can also create your C++ as a COM component (probably something you don't want to do) and the 3rd option you have is to add a thin layer of C++/CLI e.g.

using namespace System;

namespace youcomany{ namespace CPPWrapper
{
    Wrapper::Function(String^ parameter)
    {
        //call the rest of you C++ from here
        }
}}