C# importing C++ dll

Question

I have a managed dll file which imports functions from a C++ dll to the managed environment. I'm using some of its functions in my program but the problem is, I get this error when I use it:

Unable to load DLL 'Libraries\lib.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

I placed the .dll file in the program's directory and in the system32 folder. However, it still doesn't work. I think I have to use DLLImport but I have no idea how to use it.. even after looking at some examples I am still confused. Can someone help me here?

Quartered

Mind telling me what details you need? – Quartered

Names of DLLs. Where they are located. The DLLImport statement. – Zita

@David, some code would help. – Ealdorman

@Ben Well, that's why I want to see the DLLimport statement. – Zita

@David Heffernan, my first comment was aimed at the op – Ealdorman

The problem is I don't have any DLLImport code, nor I do understand how it works which is why I asked here. Also, the name of the .dll file is lib.dll, and I've placed it in the program's directory/system 32 folder and several other folders but I still got that error. – Quartered

Answer 1

You say:

I placed the .dll file in the program's directory...

But:

Unable to load DLL 'Libraries\lib.dll'

We need to see your DLLImport attribute creation, i.e., the C# signature of the native method. It looks to me like you probably specify the path, i.e.,

[DllImport( "Libraries\lib.dll" )];
static extern void MyNativeMethod();

Try using this instead:

[DllImport( "lib.dll" )];
static extern void MyNativeMethod();

That will search the running directory as well as through your PATH environment variable. If you specify a file path as you do I honestly don't know if it will search through PATH if the file is not found (I couldn't find mention of it in the docs).

Mariellamarielle

Answer 2

There isn't enough information here to help, as you're not showing the API (in native code) you're trying to import, etc.

That being said, I'd strongly recommend reading the Platform Invoke Tutorial as well as A Closer Look at Platform Invoke on MSDN. They walk through the main issues, as well as showing many examples of how to import and use functions from a C++ DLL.

Numeral

Answer 3

The best and easiest way of using a c++ dll file in c# :-

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;

namespace demo1
{
    class Program
    {
        [DllImport("shi.dll", EntryPoint = "?HelloWorld@@YAXXZ")]
       public static extern int HelloWorld();
      public  static void Main(string[] args)
        {
            //Console.WriteLine(StringUtilities.HelloWorld());
            Console.WriteLine(HelloWorld());
            // public static extern void HelloWorld();
           //  HelloWorld();
            //  Console.ReadKey();
        }
    }
}

Wyndham

Answer 4

If you are sure of the exports (use dependancy walker to check) and that you have correctly mapped them using the correct PInvoke calls, then your issue might be 32/64 bit related especially if you are on a 64bit OS with a .NET application set to Any CPU.

A 32 bit native DLL can only be loaded by a 32 bit .NET process when using PInvoke (the same applies to 64 bit native DLLs).

You can change the platform target using Properties->Build->Platform target or you can use the CorFlags utility.

Riocard

Answer 5

I faced the same issue with different .dll file , the solution was to change the target to x64 instead of x86

Prickett