Using C++ DLL in C# project

Question

Using C++ DLL in C# project

I got a C++ dll which has to be integrated in a C# project.

I think I found the correct way to do it, but calling the dll gives me this error: System.BadImageFormatException: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

This is the function in the dll:

extern long FAR PASCAL convert (LPSTR filename);

And this is the code I'm using in C#

namespace Test{
public partial class Form1 : Form
{
    [DllImport("convert.dll", SetLastError = true)]
    static extern Int32 convert([MarshalAs(UnmanagedType.LPStr)] string filename);

    private void button1_Click(object sender, EventArgs e)
    {
        // generate textfile
        string filename = "testfile.txt";

        StreamWriter sw = new StreamWriter(filename);
        sw.WriteLine("line1");
        sw.WriteLine("line2");
        sw.Close();

        // add checksum
        Int32 ret = 0;
        try
        {
            ret = convert(filename);

            Console.WriteLine("Result of DLL:  {0}", ret.ToString());
        }
        catch (Exception ex)
        {
            lbl.Text = ex.ToString();
        }
    }
}}

Any ideas on how to proceed with this?

Thanks a lot, Frank

c#

c++

dll

dllimport

asked on Stack Overflow Jun 8, 2010 by

Frank

4 Answers

Try to switch your C# code from AnyCPU to x86 (in Properties dialog).

answered on Stack Overflow Jun 8, 2010 by

Josip Medved

Your exported function uses the PASCAL calling convention, which in Windows is the same as stdcall. The .Net runtime needs to know about that, so modify your C# method signature as follows:

[DllImport("convert.dll", SetLastError = true, CallingConvention=CallingConvention.StdCall)]
static extern Int32 convert([MarshalAs(UnmanagedType.LPStr)] string filename);

answered on Stack Overflow Jun 8, 2010 by

Frank Bollack • edited Jun 8, 2010 by

Frank Bollack

try to use __stdcall (or WINAPI or APIENTRY) in the function exported from the DLL.

answered on Stack Overflow Jun 8, 2010 by

Oleg

Two main steps involved are

1- Creating a C++ dll

In visual studio

**New->Project->Class Library** in c++ template Name of project here is first_dll in visual studio 2010. Now **declare your function as public** in first_dll.h file and write the code in first_dll.cpp file as shown below.

Header File

Cpp File

Check **Project-> Properties -> Configuration/General -> Configuration Type** 
this option should be **Dynamic Library(.dll)** and build the solution/project now.

first_dll.dll file is created in Debug folder

2- Linking it in C# project

Open C# project

Rightclick on project name in solution explorer -> Add -> References -> Browse to path
where first_dll.dll is created and add the file

Add this line at top in C# project

Using first_dll;

Now file can be accessed using below statement in some function

double var = Class1.sum(4,5);

I linked the C++ project .dll created in VS2010 to C# project created in VS2013. It works well.

answered on Stack Overflow Dec 31, 2015 by

Croko

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