Marshaling code2 : Problem described below

Question

Though I don't know VC++ have I've searched the net. Please check it...

 

The VC++ code:-

 

a)plus.h:

#ifndef PLUS_H
#define PLUS_H
int __declspec(dllexport) add(int a, int b);
#endif

b)plus.cpp:

#include "pch.h"
#include "plus.h"
int add(int a, int b)
{
return a + b;
}

Now in C#

public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Test t = new Test();
int fooPtr = Test.add(5, 9);
int LENGTH = 1;
var foo = new int[LENGTH];
/// Marshal.Copy(fooPtr, foo, 0, LENGTH);
MessageBox.Show(fooPtr.ToString());
}
}
public class Test
{
[DllImport("F:/TestMultipleProject/FirstDll/Debug/FirstDll.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
public static extern int add(int a, int b);
}

Reference of VC ++ project is added to C# and they both reside in same solution

 

NOW PROBLEM is unable to find an entry point named add in the dll....