dll import (Unable to find an entry point named "methodname" )

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I am trying to import a c++ dll into my C# windows project. But i am getting an error "Unable to find an entry point named 'Add' in DLL 'Test.dll'"

My c++ source code:

C#

#pragma once

using namespace System;

namespace Test {

    public ref class Class1
    {
    public: int Add(int i, int j)
        {
            return(i + j);
        }
    };
}

My C# windows source code:

C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using Test;// my c++ dll refernce


namespace WindowsApplication3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        [DllImport("Test.dll")]
        public static extern int Add(int a, int b);
        private void button1_Click(object sender, EventArgs e)
        {
            int p = Add(1, 2);
        }
    }
}

I placed the c++ dll in c# application output path i e debug folder.

Please help to find me the error i made in the c++ or c# code.

Posted 27-Jul-12 2:40am

code4Better

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[no name] 27-Jul-12 9:03am

You need to export your "Add" function.

code4Better 30-Jul-12 3:13am

I tried exporting the function and even the class itself as shown below. But still am getting same error. Please help!

#pragma once

using namespace System;

namespace Test {

public class __declspec(dllexport) Class1
{
public:static int Add(int i, int j)
{
return(i + j);
}
};
}

4 solutions

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Richard MacCutchan · Answer 1 · 2012-07-27T03:51:00

Solution 1

Your Add() function is a member of Test::Class1 and yet in your C# code you define it as public static. Change it to a stand-alone function not in any namespace or class and export its name, like this:

C++

__declspec(dllexport) int Add(int i, int j)
{
    return(i + j);
}

Posted 27-Jul-12 3:51am

Richard MacCutchan

Comments

code4Better 30-Jul-12 4:51am

I tried exporting the function and even the class itself as shown below. But still am getting same error. Please help!
#pragma once using namespace System;
namespace Test
{
public class __declspec(dllexport) Class1
{
public:static int Add(int i, int j)
{ return(i + j);
}
};
}

Richard MacCutchan 30-Jul-12 5:57am

I have not been able to get this to work, and tried a Google search for help. The answer, as shown in some of these links, would appear to be that it is not possible.

code4Better 31-Jul-12 6:06am

Any way thank you very much Mr.Richard

OriginalGriff · Answer 2 · 2012-07-27T03:52:00

Solution 2

You need to export your function from the C++ class using __declspec(dllexport)

http://msdn.microsoft.com/en-us/library/a90k134d(v=vs.80).aspx[^]

Posted 27-Jul-12 3:52am

OriginalGriff

Comments

code4Better 30-Jul-12 4:51am

I tried exporting the function and even the class itself as shown below. But still am getting same error. Please help!
#pragma once using namespace System; namespace Test
{
public class __declspec(dllexport) Class1
{
public:static int Add(int i, int j)
{ return(i + j); }
};
}

Ruselo Riva Asentista · Answer 3 · 2012-07-27T07:06:00

Solution 3

The default directory of DLLImport is the Windows/System32 directory, not your application. You need to specify the location of your dll in absolute terms like

[DllImport("Test.dll")]

Check this out for an example of DLLImport:

http://www.pinvoke.net/default.aspx/user32.CascadeChildWindows[^]

Posted 27-Jul-12 7:06am

Ruselo Riva Asentista

Comments

code4Better 30-Jul-12 3:13am

fds

code4Better 30-Jul-12 4:53am

I tried exporting the function and even the class itself as shown below. But still am getting same error. Please help!
#pragma once using namespace System;
namespace Test
{
public class __declspec(dllexport) Class1
{ public:static int Add(int i, int j)
{ return(i + j);
}
};
}

code4Better · Answer 4 · 2012-08-02T20:54:00

Solution 4

In the above c++ code i used ref keyword which will make above c++ application as managed application. So no need to use DllImport attribute where as you can directly reference the dll(add reference in the solution explorer) and use it in C# code

Posted 2-Aug-12 20:54pm

code4Better