Unable to Call Simple Custom Dll Import from C# Application

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Update

I have now run through the tutorial 3 times with the same results (Visual Studio/Windows is unable to recognise the DLL as a valid file). This must be an issue with my environment, as mike below ran through the tutorial and it worked fine.

I did notice this in the C++ project's solution explorer on my last run:

Does anyone know if this is okay? There seems to be a lot of Red stop-signs which to me would suggest something bad...


Following this tutorial, I have ended up with the following:

C#

using System.Runtime.InteropServices;

namespace TestImport
{
    class Program
    {
        [DllImport("TestLib.dll")]
        public static extern void DisplayHelloFromDLL();

        static void Main(string[] args)
        {
            DisplayHelloFromDLL();
        }
    }
}

C++

In .cpp file Source Files

#include <stdio.h>

extern "C"
{
    __declspec(dllexport) void DisplayHelloFromDLL()
    {
        printf("Hello from DLL !\n");
    }
}

When debugging in Visual Studio:

An unhandled exception of type 'System.DllNotFoundException' occurred in TestImport.exe

Additional information: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

When running the built EXE (from he same folder as the Dll):

An attempt was made to load a program with an incorrect format.

Have I done anything wrong in the above code? I did do all of this in VS 2015, where the tutorial calls for VS 2010, howeve rI couldn't find a more up-to-date tutorial.


When I try to add the project as a reference by Project -> Add Reference ... I am seeing this error:

A reference to 'Path\To\MyLib.dll' could not be added. Please make sure 
that the file is accessible, and that it is a valid assembly or COM
component.

Which makes me think that the issue is either with the source code or the DLLs configuration.

I have also tried building both files and putting them in the same folder before running the Executable, but without any improved results (same error as when running the EXE above).


Solution Explorer Screenshot:

Make sure the name of your C++ project and DllImport parameter are the same. Also, if the dll file is not located in the same directory as your C# project, make sure to add the dll into your Debug/Release folder.

Also! Make sure that you are running in the same 32/64 bit mode when compiling.. if you compiled the dll using 32 bit and try to use it in a 64 bit C# program, it won't work.

Unmanaged C++ Dll Call From Managed C# Application, Unmanaged C++ Dll Call From Managed C# Application. Tanmay Sarkar; Updated Here, you will learn the steps for using a simple C++ DLL in C# in . [ DllImport("OurDll.dll", CallingConvention = CallingConvention.Cdecl)]� Here, you will learn the steps for using a simple C++ DLL in C# in .NET Framework 4. Open Visual C++ Win 32 Project. In Application Settings, chose "DLL" and select "Empty Project".

OK, now build this application, and then copy the previously built DLL into the Debug/Release directory of the current application. The DLL should be in the same directory as your main application.

Did you do the bolded text? Your C# app won't know where to look for the DLL and it looks in the build folder, by default.

NET Column: Calling Win32 DLLs in C# with P/Invoke, In this column I am going to focus on the practical use of P/Invoke for calling Windows API functions. This information is provided by the DllImport custom attribute that So making P/Invoke calls to the Windows API is easy in C#. For example, in Figure 1 I converted a Boolean failure returned by the� 10/22/2019; 29 minutes to read; In this article.NET. Calling Win32 DLLs in C# with P/Invoke. Jason Clark. Code download available at:NET0307.exe(133 KB) Contents. Enter P/Invoke Style The DLL Import Attribute Optional DllImportAttribute Properties Data Marshaling Marshaling Numerical and Logical Scalars Parameters that are Pointers Marshaling Opaque Pointers: a Special Case Marshaling Text

An unhandled exception of type 'System.DllNotFoundException'

It happened to me, because of the imported c++ dll, its own dependency dlls were missing.

After copying them into Debug/Release folder everything worked.

Calling Native Functions from Managed Code, Using Explicit PInvoke in C++ (DllImport Attribute) PInvoke can simplify customized data marshaling because you provide The following sample is equivalent to the previous sample, but uses IJW. C++ If the application uses mainly unmanaged data types or if it calls more unmanaged APIs than . Step 1 - Open Visual Studio then select "File" -> "New" -> "Project" then select "Visual C#" -> "Windows Forms application". Step 2 - Design the form as in the following image: Step 3 - Add a reference for the dll file, "calculation.dll", that we created earlier.

Link an executable to a DLL, Implicit linking occurs when an application's code calls an exported DLL function. The import library only contains code to load the DLL and to implement calls To resolve external references to DLLs, the linker simply adds information to if any of the DLLs it's linked to have a DllMain function that fails. I have a basic C# Universal App that imports a very simple unamanged c++ dll and uses p/invoke to call a functions. The code works fine in a standard WPF Application but the Universal Application returns a "Unable to load dll

Walkthrough: Create and use your own Dynamic Link Library (C++) , Use C++ to create a Windows dynamic-link library (DLL) in Visual Studio. conventions, see Exporting C++ functions for use in C-language executables. NET languages, see Calling DLL Functions from Visual Basic Applications. Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========. I tried to get the correct path of the web application DLL by using Assembly.GetCallingAssembly().Location, thinking that the calling assembly inside the provider would be the web application assembly. That call would return the path to the web application assembly where I could copy 'fbembed.dll' during runtime. This turned out to be very

7. Use the DLL in your VBA code. To use the variables and methods in the C# DLL, we need to call the DLL inside VBA. Add a button to the Access form and then add a click event to it. In the click event we call a function called test() which is created within a VBA module.

Comments
  • Make sure the C++ library's output folder matches where the C# project's output folder is or make a pre-build step that copies to that location (the C++ dll will need to be in the same folder as the C# application).
  • Hi crashmstr, thanks for your comment. I have built both projects and put them in the same folder but with the same error. I have also added the dll into the c# debug/release folder but this doesn't help either. Does this seem like the issue is with the dll itself?
  • You can get that error if some other DLL dependency of the DLL you are using cannot be found, but that would not seem likely here.
  • And since it is not a .Net DLL or a COM dll, then you cannot add a reference (this is normal).
  • Hi Mike thanks for your answer - do you mean change the name of the Dll to TestImport.Dll before building, or is this what I should change the call to?
  • I have tried all of these but with no help - are there any config settings in the dll which I can try changing?
  • You have physically copied the <C++ PROJ NAME>.dll from the Debug/Release folder of the C++ project and pasted it into the Debug/Release folder of your 'C#' project?
  • If you have done this, and ensured that TestLib.dll is the same exact name as the .dll you generated from the C++ project, this should work.
  • Yes I copied the dll into the Debug/Release folder, and the name of the project and final .dll matches that called in the EXE - Perhaps there is a setting I need to change in VS ...
  • Hi Khale, yes I tried this but with no luck! I even added both the completely built EXE and DLL in the same folder but without any improvement!