Using a C++ dll in a C# application

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I want to write a dll in C++ as a class library and call it’s methods in a C# program.

Note, with the VS 2010 C++ Express edition there is no MFC DLL. I have to put my methods in a C++ class and compile it to a DLL using the Class Library option.

Again, how do I call those C++ methods in C#. A code snippet, a website, or exactly what to type into my search engine would be appreciated.

I'm using VS 2010 Express for both C++ and C#.

Posted 3-Sep-10 8:32am

firmwaredsp

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4 solutions

Solution 3

Below is the C++ part.

Visual Studio 2010 C++
New project
Win32 Console Application
Name: calculator
Application type: DLL

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

#include stdafx

static double Add (double x, double y)
{
return (x+y);
}
The above builds successfully as “calculator.dll”

----------------------------------------------------------

Below is the C# code
// Form1.cs
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{

[DllImport("calculator.dll", EntryPoint = "Add")]
public static extern double Add(double x, double y);

public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{

label1.Text = Add(2.2, 3.4).ToString();
}

}
}

The C# program built and ran till I clicked on button1. The following exception was generated:
“EntryPointNotFoundException was unhandled”

Unable to find an entry point named Add in DLL ‘calculator.dll'

Posted 4-Sep-10 10:56am

firmwaredsp

Updated 4-Sep-10 13:00pm

v2

Solution 2

Hi,

do you mean MC++?!
If so you can easily reference it in c# and use it.
But if you want to write a dll in VC++ ( I mean unmanaged code), then you have to do what Lantei said.

Posted 3-Sep-10 14:00pm

aidin Tajadod

Solution 4

OK,
you need to define them in your c++ dll.
To do so add a .def file to your project and enter your functions name in it like this:

VB

LIBRARY calculator

EXPORTS
Add @1

So whole your def file should be like that.
hope this can help you.

Posted 13-Sep-10 11:06am

aidin Tajadod

Updated 13-Sep-10 11:10am

v2

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Lantei · Accepted Answer · 2010-09-03T09:17:00

ok first..C# has support for unmanaged code (which your case will be) since you're writing it in C++ (but if you'll be using VC++, It will be managed then).

Now after creating the DLL file (and pls remember to save it as a .DLL), you'll use the System.Runtime.InteropServices (which handles managed-unmanaged code interoperability) namespace of .NET to do your import

so first..add the System.Runtime.InteropServices namespace to your code..

and then follow the code sample below..which imports a DLL named : msvcrt and access the int typed method in it named : puts(string _c)

--remember that you do the DLL imports for each method called--

C#

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

class PlatformInvokeTest
{
    /* DLL Import with 1st method */
    [DllImport("msvcrt.dll")]
    public static extern int puts(string c);

    /* DLL Import with 2nd method */
    [DllImport("msvcrt.dll")]
    internal static extern int _flushall();

/* Methods in DLL being used below  */
    public static void Main()
    {
        puts("Test");
        _flushall();
    }
}

but I must add that depending on what you want to do with the DLL, there are quite a number of things you can do (optional), such as Marshalling, assigning Entry Point, etc..So I would suggest you read some articles on it..There are loads of them online

If you like the above, Accept Answer and give a Vote.. :)