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How to create a DLL library in C and then use it with C#

, 13 Mar 2005
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An easy-to-use example of how to create a DLL library in C and then use it with C#.


After spending some time trying to implement this simple task, I started to search similar code examples over the Internet. I was really very surprised when found that all examples were slightly different from what I needed. Finally, I realized that there is no (at least spending 30 min in the net) easy-to-use example, that’s why I decided to write this article.

Assuming that you already know what a DLL is, let's begin with creating a simple one.

  1. Start Visual Studio .NET.
  2. Go to File->New->Project.
  3. Select Visual C++ Project, and from the “Templates”, select “Win32 Project”.
  4. Give the name to your project. This will be the name of your final DLL (in my case: TestLib).
  5. Press OK.
  6. Select DLL from “Application Type” (“Application Settings” tab).
  7. Check “Empty Project” (we need to create our project from scratch, right?), and press Finish.

OK, now we should attach an empty source file to our blank project.

  1. Start Solution Explorer (if it’s not displayed).
  2. Right click to the “Source Files”, Add->Add New Item then select “C++ File” and give the name to it.
  3. Press “Open”.

In the opened window, enter the following code:

#include <stdio.h>

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

Please note that __declspec(dllexport) is an obligatory prefix which makes DLL functions available from an external application.

extern “C” (with brackets) is also very important, it shows that all code within brackets is available from “outside”. Although code will compile even without this statement, during runtime, you’ll get a very unpleasant error. So, do not forget to include it.

Build this application and your DLL will be ready-to-use.

Now it’s time to create an application which will use our DLL, as the main title explains. We will create this type of application using Microsoft’s C#.

Creating a simple C# application:

  1. Start Visual Studio .NET.
  2. Go to File->New->Project.
  3. Select Visual C# Project. From the “Templates”, you can either select “Console Application”, or an “Empty Project” just like it was described above.
  4. Give the name to your application.
  5. Press OK.

Into the specified class, insert the following two lines:


public static extern void DisplayHelloFromDLL ();

In C#, keyword extern indicates that the method is implemented externally.

Your code should look something like this:

using System;
using System.Runtime.InteropServices;     // DLL support

class HelloWorld
    public static extern void DisplayHelloFromDLL ();

    static void Main ()
        Console.WriteLine ("This is C# program");
        DisplayHelloFromDLL ();

Please, note that System.Runtime.InteropServices is required for operations with the DLL.

According to MSDN:

“The System.Runtime.InteropServices namespace provides a collection of classes useful for accessing COM objects, and native APIs from .NET”

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.

Now start an application. If everything you’ve made was correct, you should get something like this:

That’s all, really simple isn’t it?


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Vladimir Tskhvaradze
United States United States
No Biography provided

Comments and Discussions

GeneralRe: My vote of 2 Pinmemberfiras_hamzeh23-Jun-10 11:04 
GeneralRe: My vote of 2 PingroupDaveGordon16-Aug-13 6:27 
Generalgreat article and thanks Pinmembermickyzhang12-Jan-10 7:30 
General"An attempt was made to load a program with an incorrect format" [modified] Pinmemberlonik.r21-Jul-09 23:50 
GeneralRe: "An attempt was made to load a program with an incorrect format" Pinmembergentry_joey13-Dec-09 9:29 
QuestionHow to use this .dll and .exe in a System, which having only .net frame work, (not Visual Studio) PinmemberMember 377636727-Nov-08 2:14 
QuestionDo you Think it is working ?? PinmemberMember 339892412-Oct-08 21:15 
AnswerRe: Do you Think it is working ?? PinmemberJonghoon Han19-Nov-08 6:34 
Please try not to take this the wrong way.
I'm afraid that what you've come upon was caused by your careless.
As you saw in the article above, it does work well.
All you need to do is place the DLL you want to use in the same directory as the application you're going to run.
Everything happens for a purpose and reason, and it serves us.

QuestionHow Do i Create a MyLib Pinmembervijaymunnoli12-Jun-08 1:09 
QuestionWhy doesn't this work with Visual Studio 2005 Pinmembercanhestros3-Apr-08 4:44 
GeneralRuntime exception while loading dll [modified] Pinmemberparazitu3-Nov-07 3:52 
GeneralReally helped me. Pinmemberramachandragowda2-Oct-07 6:31 
GeneralNice code Pinmemberbijulsoni16-Aug-07 14:23 
Questionwhat about using classes Pinmembersoorajvs200513-Aug-07 1:14 
QuestionDoes not work on other pc PinmemberRafan31-May-07 12:59 
AnswerRe: Does not work on other pc [modified] PinmemberMichael900028-Jun-08 14:18 
GeneralEmbedded Resource in .NET Pinmembertanveerakl4-Jul-06 0:48 
Generalreleasing resources Pinmemberfatih isikhan5-Dec-05 4:08 
QuestionUsing strings parameters in C++ DLL PinmemberBillMcNeil1-Dec-05 9:05 
Generalextern not necessary PinmemberMark Zudeck27-Oct-05 9:55 
GeneralNice article ! Pinmemberddmcr17-Oct-05 11:01 
Generalexport/import a class... Pinmemberd00_ape20-Jun-05 5:13 
QuestionCreate Dll library in C and then use it with C#, but can I create Dll Library in C# and then use it with C, VC/C++ ? PinsussLiTaiNien17-Jun-05 19:18 
GeneralMarshalling Pinmemberpjcrosbie8-Apr-05 18:19 
Questionhow to create reusable library(DLL),using recursive algorithms? Pinmemberdcvam3-Apr-05 18:39 

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