dll used in C# application in VS2005 works correctly, but didn't work in VS2012.

[sreehari_mysore]

I am using a dll developed in Visual c++ in to the C# application. It works fine with Visual Studio 2005. But when using the same with Visual Studio 2012, it causes the error.

myDll.h

#ifndef _MYDLL_H
#define _MYDLL_H

extern "C" _declspec(dllexport) char* __stdcall getName();

#endif

myDll.cpp

#include "stdafx.h"

#include "mydll.h"

extern "C" __declspec(dllexport) char* __stdcall getName()
{
return "Hello !!!";
}

the above code produces the mydll.dll. I used to copy the dll into newly created c# windows application into bin/Debug directory. The c# application code is somewhat like

using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace sysWinApp
{
public partial class Form1 : Form
{
[DllImport("myDll.dll")]
static extern string getName();

    public Form1()
    {
        InitializeComponent();
    }

    private void button1\_Click(object sender, EventArgs e)
    {
        label1.Text = getName();
    }
}

}

the windows form consists of a label and a button. By clicking the button, it should display the content on the label, which is accessed from the string returned from the dll function. It works fine with VS2005 but the same didn't happen with VS2012. The C# win app of VS2012 prompts the message that it "has stopped working". any ideas to resolve this ?

[Freak30]

I'm not sure how you ever got this working in VS2005. There are two issues. First: You can't return a pointer to a char array that you allocated on the stack. The moment the funtion returns the memory is deallocated and a pointer to an unallocated address is returned. You need to allocate the memory using new. This implies that you need to export an additional function that receives a pointer and deletes it (to prevent memory leaks). Second: In your C# application you define (incorrectly) that the imported function returns a (managed) string. Actually it returns a char pointer. I think you will need an unsafe block to receive the char pointer, initialize a new managed string with it and then delete the char pointer (using the function mentioned above). After that you can assign the managed string to the label.

The good thing about pessimism is, that you are always either right or pleasently surprised.

[sreehari_mysore]

I developed this application by referring to the example in codeproject. please refer the below link Using Unmanaged code and assembler in C#[^]

[Bernhard Hiller]

The C dll is a 32bit dll (as was your VS2005 application), while your VS2012 application is a 64bit application (or a bitness-ignoring application on a 64bit system).