Question

I am currently trying to use a simple C++ DLL in a C# program for a school project but I have trouble making the DLL and Program link with each other. When I try to call the DLL’s function in the main program, I get a SEHExcpetion thrown from the DLL.

Here is the DLL code

#include <stdio.h>
#include <string>

using namespace std;

extern "C"
{
    __declspec(dllexport) string Crypter(string sIn)
    {
        return sIn+ " from DLL";
    }
}  

And here’s the C# code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        [DllImport("CryptoDLL2.dll")]
        public static extern string Crypter(string sIn);

        public Form1()
        {
            InitializeComponent();
        }

        private void BTN_Crypter_Click(object sender, EventArgs e)
        {
            TB_OUT.Text = ("");
            TB_OUT.Text = Crypter(TB_IN.Text); //exception thrown here
        }
    }
}

Answer 1

Strings in C# and C++ – Those are completely different types, layouts, etc. And you expect them to work.

Check out char* with marshalling.