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

, 13 Mar 2005 331.8K 5.5K 108
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An easy-to-use example of how to create a DLL library in C and then use it with C#.

Introduction

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:

[DllImport("TestLib.dll")]

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
{
    [DllImport("TestLib.dll")]
    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?

License

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

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About the Author

Vladimir Tskhvaradze
Other
United States United States
No Biography provided

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Comments and Discussions

 
QuestionDo you Think it is working ?? Pin
Member 339892412-Oct-08 20:15
memberMember 339892412-Oct-08 20:15 
AnswerRe: Do you Think it is working ?? Pin
Jonghoon Han19-Nov-08 5:34
memberJonghoon Han19-Nov-08 5:34 
QuestionHow Do i Create a MyLib Pin
vijaymunnoli12-Jun-08 0:09
membervijaymunnoli12-Jun-08 0:09 
QuestionWhy doesn't this work with Visual Studio 2005 Pin
canhestros3-Apr-08 3:44
membercanhestros3-Apr-08 3:44 
GeneralRuntime exception while loading dll [modified] Pin
parazitu3-Nov-07 2:52
memberparazitu3-Nov-07 2:52 
GeneralReally helped me. Pin
ramachandragowda2-Oct-07 5:31
memberramachandragowda2-Oct-07 5:31 
GeneralNice code Pin
bijulsoni16-Aug-07 13:23
memberbijulsoni16-Aug-07 13:23 
Questionwhat about using classes Pin
soorajvs200513-Aug-07 0:14
membersoorajvs200513-Aug-07 0:14 
QuestionDoes not work on other pc Pin
Rafan31-May-07 11:59
memberRafan31-May-07 11:59 
AnswerRe: Does not work on other pc [modified] Pin
Michael900028-Jun-08 13:18
memberMichael900028-Jun-08 13:18 
GeneralEmbedded Resource in .NET Pin
tanveerakl3-Jul-06 23:48
membertanveerakl3-Jul-06 23:48 
Generalreleasing resources Pin
fatih isikhan5-Dec-05 3:08
memberfatih isikhan5-Dec-05 3:08 
QuestionUsing strings parameters in C++ DLL Pin
BillMcNeil1-Dec-05 8:05
memberBillMcNeil1-Dec-05 8:05 
Generalextern not necessary Pin
Mark Zudeck27-Oct-05 8:55
memberMark Zudeck27-Oct-05 8:55 
You say that "extern "C"" means that "all code ... is available from "outside"". Actually, in C++, when used with a string, extern specifies that things are declared with the linkage conventions of another language. In this case, the language is "C".

However, the extern specification is unnecessary if you don't create a C++ DLL. Your article's title says that we will create a DLL in C. After you create your empty DLL project and add a file to it, why not just save the file with a ".c" extension, instead of ".cpp"? Then you don't need the language linkage modifier in the code at all.

Mark Zudeck
mark@zudeck.com
GeneralNice article ! Pin
ddmcr17-Oct-05 10:01
memberddmcr17-Oct-05 10:01 
Generalexport/import a class... Pin
d00_ape20-Jun-05 4:13
memberd00_ape20-Jun-05 4:13 
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++ ? Pin
LiTaiNien17-Jun-05 18:18
sussLiTaiNien17-Jun-05 18:18 
GeneralMarshalling Pin
pjcrosbie8-Apr-05 17:19
memberpjcrosbie8-Apr-05 17:19 
Questionhow to create reusable library(DLL),using recursive algorithms? Pin
dcvam3-Apr-05 17:39
memberdcvam3-Apr-05 17:39 
GeneralImportant: Handling bool returns Pin
Mark Jerde30-Mar-05 4:59
memberMark Jerde30-Mar-05 4:59 
GeneralC# calling a Cpp dll Pin
SHG28-Mar-05 21:25
memberSHG28-Mar-05 21:25 
Generalgreat article Pin
Nik Vogiatzis27-Mar-05 3:12
memberNik Vogiatzis27-Mar-05 3:12 
GeneralC# dll like C dll Pin
msali26-Mar-05 3:06
membermsali26-Mar-05 3:06 
GeneralRe: C# dll like C dll Pin
Roman Antchik28-Mar-05 12:15
memberRoman Antchik28-Mar-05 12:15 
GeneralRe: C# dll like C dll Pin
msali28-Mar-05 18:57
membermsali28-Mar-05 18:57 
GeneralRe: C# dll like C dll Pin
Roman Antchik28-Mar-05 19:41
memberRoman Antchik28-Mar-05 19:41 
QuestionHow about Strong Names Pin
msali26-Mar-05 3:01
membermsali26-Mar-05 3:01 
AnswerRe: How about Strong Names Pin
Roman Antchik28-Mar-05 19:46
memberRoman Antchik28-Mar-05 19:46 
GeneralCalling function which returns a string from Unicode DLL Pin
NikolaiT25-Mar-05 7:25
memberNikolaiT25-Mar-05 7:25 
GeneralNice, but what about the other way around Pin
Anonymous23-Mar-05 9:06
sussAnonymous23-Mar-05 9:06 
GeneralRe: Nice, but what about the other way around Pin
LiTaiNien17-Jun-05 18:21
sussLiTaiNien17-Jun-05 18:21 
GeneralNice, but what about the other way around Pin
Anonymous23-Mar-05 9:06
sussAnonymous23-Mar-05 9:06 
QuestionInterop DLL? Pin
Ben Bryant14-Mar-05 2:15
memberBen Bryant14-Mar-05 2:15 

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