Unable to find an entry point named 'Add' in DLL 'CPPDLL.dll'. while running a c#.net web application


I have created a small web application using c#.net that calls a function from a dll file created in c++

the following are the files that i have used to create a dll file..

//CPPDLL.cpp file

#include “stdafx.h”

#include “CPPDLL.h”

using namespace std;

namespace CPPDLL
double Class1::Add(double a, double b)
return a + b;

//CPPDLL.h file

#pragma once

using namespace System;

namespace CPPDLL {

public class Class1
// TODO: Add your methods for this class here.
static __declspec(dllexport) double Add(double a, double b);


Now my c#.net code is as follows

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using CPPDLL;
using System.Runtime.InteropServices;

public partial class _Default : System.Web.UI.Page

[DllImport("CPPDLL.dll", EntryPoint="Add")]

private static extern double Add(double a, double b);

protected void Page_Load(object sender, EventArgs e)

protected void Button1_Click(object sender, EventArgs e)
double sum = Add(12, 13);

After running the application when i press the button the following error is displayed…..

Unable to find an entry point named ‘Add’ in DLL ‘CPPDLL.dll’.

help me please in finding the problem…

Keerthi raj
9/16/2008 4:43:50 AM
asp.net.getting-started 91979 articles. 3 followers. Follow

3 Replies

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Looked at your code, the only thing as of now i can point you to is the signature of the Add method.  The signature of the add method in the CPPDLL is double Class1::Add(double a, double b), by not specifying the access modifier i believe it is public by default in c++ and its is private in c#. and in your c# code you have private static extern double Add(double a, double b);. This gives me a feeling of signature mismatch. Try removing the private access modifier in your c# and see what happens and let us know.




9/16/2008 8:43:59 AM

 the same error is occuring...even after changing the access modifier

Keerthi raj
9/16/2008 1:36:32 PM


 you most to declare the follow code:


Native DLL C/C++:

Sample DLL "CPPDLL.dll"

in the ".h"

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

 in the ".c" or ".cpp"

__declspec(dllimport) double Add(double x, double y)


       return (x*y);



From C# Component:

 public class ImplementNativeDll


     [DllImport(@"CPPDLL.dll", EntryPoint="Add")]

     public extern static double Add( double x, double y);


public class ExecuteCode


        public static void Main()


                 double xy = ImplementNativeDll.Add( 6.0, 5.0 );

                  System.Console.WriteLine("Result: {0}", xy);






Developer Senior





10/30/2008 5:45:24 PM

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