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Posted 10 Sep 2004


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Dlls are Simple. Part 1

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8 Oct 20042 min read
How to create DLLs and use them.

Sample screenshot


Some programmers think DLLs are complicated but it's true they are like EXEs. However I have seen programmers who can't build DLL. There are multiple way to create a DLL. For usage with exe, easiest way is "Implicit linking". In this way, we require .LIB file produced by DevStudio. Below, we create a DLL and then use it with exe. Inside DLL, we calculate (multiply) two numbers that has been send from the exe. Practically, exe is "Sender/Receiver" and DLL is "Calculator".

How to build MFC DLL?

  1. Run VC++.
  2. Choose : File > New.
  3. Create "MFC AppWizard (DLL)" (named e.g. : MyFirstDll).
  4. Declare in top of file:
    #define DLLEXPORT __declspec(dllexport)

    __declspec(dllexport)'s purpose is to add the " export directive " to the object file. So you don't need a .DEF file. To make code more readable, define a macro for __declspec(dllexport) : DLLEXPORT.

  5. Now for exporting per function that you want, type before it : "DLLEXPORT" like this:
    DLLEXPORT int Multiply(int ParOne,int ParTwo) 
       int Mlt=ParOne*ParTwo; 
       return Mlt; 
  6. Press Build button.
  7. Bring out DLL from oven!!

    Note that linker also builds an " import library " with the same DLL name but with .lib extension.

How to use MFC DLL?

  1. Run VC++.
  2. Choose : File > New.
  3. Create "MFC AppWizard (exe)".
  4. Choose "Dialog based".
  5. Choose : Project > Add To Project > New > C/C++ Header File.
  6. Name file e.g. : Imports.
  7. Declare in Imports.h:
    #define DLLIMPORT __declspec(dllimport) 

    __declspec(dllimport)'s purpose is to add the " import directive " to the object file. To make code more readable, define a macro for __declspec(dllimport) : DLLIMPORT.

  8. Type after it:
    DLLIMPORT int Multiply(int ParOne,int ParTwo);

    This is the same function that you defined in DLL. Here, it has been introduced as an "import function". But it is unrecognized for current project and we must resolve it for linker.

  9. Copy .lib file from release or debug folder (depends current project setting) in previous project to current directory project because it must link with exe. Inside .lib file (same import library), exists information about exported functions of DLL.
  10. Back to VC++ environment and Choose : Project > Settings > Link (tab).
  11. Type [.lib file previous project] in "Object/library modules:". For example, MyFirstDll.lib. Then press OK. It will resolve externals. Here, "int Multiply(int ParOne,int ParTwo);" function.
  12. Because we intend to use function in ...Dlg.cpp file (e.g. SimpleDllDlg.cpp), type in top of file:
    #include "Imports.h"
  13. Now you can use exported function of DLL like this:
    void CDllFunDlg::OnMltply() 


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Written By
Web Developer
Iran (Islamic Republic of) Iran (Islamic Republic of)
I born in tehran at 1975
and began programming with commodore 64
I established "Pishro Narmafzar Iran" Corporation in 2001.
i'm expert in VC++, VC#, MS SQL Server, ASP .NET & have developed :
1-Persian Photoshop (fully localized)
2-Persian Freehand (fully localized)
3-Pardis (persian/arabic typing in graphical and video editing programs include : Ulead video studio,Ulead media studio,Pinnacle studio, Premiere, Flash, Freehand, 3D Max, Auto CAD, Photoshop, CorelDraw, Ulead Cool 3D,...)
Pardis is only persian/arabic typing tool for Ulead Video Studio in world.
Mahmoud komeily, mahmood komeili, محمود کمیلی

Comments and Discussions

Questioni lose .lib Pin
raid_zh27-Mar-07 22:20
Memberraid_zh27-Mar-07 22:20 
AnswerRe: i lose .lib Pin
Mahmoud Komeily30-Mar-07 12:30
MemberMahmoud Komeily30-Mar-07 12:30 
GeneralRe: i lose .lib Pin
raid_zh11-Apr-07 23:00
Memberraid_zh11-Apr-07 23:00 
GeneralDLL's Pin
Huntedwabbit22-Feb-05 18:57
MemberHuntedwabbit22-Feb-05 18:57 
GeneralRe: DLL's Pin
Mahmoud Komeily13-Apr-05 9:14
MemberMahmoud Komeily13-Apr-05 9:14 
GeneralHow do I use a dll that contains a dialog? Pin
udiraz20-Dec-05 21:58
Memberudiraz20-Dec-05 21:58 
GeneralHow do I use a dll that contains a dialog? Pin
udiraz20-Dec-05 22:02
Memberudiraz20-Dec-05 22:02 
GeneralThank You!!!! Pin
Anonymous13-Dec-04 0:28
MemberAnonymous13-Dec-04 0:28 
GeneralRe: Thank You!!!! Pin
Mahmoud Komeily20-Dec-04 18:12
MemberMahmoud Komeily20-Dec-04 18:12 
GeneralA Good one 5 out of 5 from me... Pin
Jigar Mehta7-Oct-04 18:16
MemberJigar Mehta7-Oct-04 18:16 
Thanks for giving such a good article... Your language is so simple, I suggest you to take hard topics and explain in your simple language... A suggestion from me to you is Templates, STL etc.

Mail me, if you put any new article about templates or STL..

Jigar Mehta

Software Developer
Gates Information Systems
GeneralRe: A Good one 5 out of 5 from me... Pin
Mahmoud Komeily8-Oct-04 23:37
MemberMahmoud Komeily8-Oct-04 23:37 
Questionhow to process strings and return from DLL Pin
acawhiz5-Oct-04 15:48
Memberacawhiz5-Oct-04 15:48 
AnswerRe: how to process strings and return from DLL Pin
Jigar Mehta7-Oct-04 18:24
MemberJigar Mehta7-Oct-04 18:24 
GeneralSalam Pin
Abbas_Riazi11-Sep-04 10:24
professionalAbbas_Riazi11-Sep-04 10:24 
GeneralRe: Salam Pin
Mahmoud Komeily11-Sep-04 10:43
MemberMahmoud Komeily11-Sep-04 10:43 
GeneralRe: Salam Pin
Abbas_Riazi11-Sep-04 11:02
professionalAbbas_Riazi11-Sep-04 11:02 
Generalvery easy & best solution Pin
antarish konam11-Sep-04 9:49
Memberantarish konam11-Sep-04 9:49 
Generaladmirable! Pin
homaioon sadeghi11-Sep-04 9:29
Memberhomaioon sadeghi11-Sep-04 9:29 
GeneralNothing special Pin
Alexander M.,10-Sep-04 14:35
MemberAlexander M.,10-Sep-04 14:35 
GeneralRe: Nothing special Pin
Mahmoud Komeily11-Sep-04 8:52
MemberMahmoud Komeily11-Sep-04 8:52 
GeneralRe: Nothing special Pin
KevinHall12-Sep-04 12:21
MemberKevinHall12-Sep-04 12:21 
GeneralRe: Nothing special Pin
Manish K. Agarwal19-Sep-04 17:34
MemberManish K. Agarwal19-Sep-04 17:34 
GeneralRe: Nothing special Pin
Mahmoud Komeily21-Sep-04 13:04
MemberMahmoud Komeily21-Sep-04 13:04 
GeneralRe: Nothing special Pin
Jerry Hammond20-Sep-04 4:14
MemberJerry Hammond20-Sep-04 4:14 
GeneralRe: Nothing special Pin
Mahmoud Komeily21-Sep-04 13:11
MemberMahmoud Komeily21-Sep-04 13:11 

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