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Dlls are Simple. Part 1

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8 Oct 20042 min read 180K   2.6K   115   40
How to create DLLs and use them.

Sample screenshot

Introduction

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() 
    { 
       UpdateData(TRUE); 
       m_Result=Multiply(m_ParamOne,m_ParamTwo); 
       UpdateData(FALSE); 
    }

License

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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

 
GeneralRe: Nothing special Pin
Jigar Mehta7-Oct-04 18:32
Jigar Mehta7-Oct-04 18:32 
GeneralRe: Nothing special Pin
quangtin31-Nov-05 15:57
quangtin31-Nov-05 15:57 
Questionnice,please help? Pin
eric naftonas10-Sep-04 13:22
eric naftonas10-Sep-04 13:22 
AnswerRe: nice,please help? Pin
Abbas_Riazi11-Sep-04 10:21
professionalAbbas_Riazi11-Sep-04 10:21 
GeneralRe: nice,please help? Pin
Jigar Mehta7-Oct-04 18:40
Jigar Mehta7-Oct-04 18:40 
Generalsimple and efficient Pin
othumo sabura10-Sep-04 12:34
othumo sabura10-Sep-04 12:34 
GeneralYeah! are fun Pin
rasen williams10-Sep-04 12:17
rasen williams10-Sep-04 12:17 
GeneralRe: Yeah! are fun Pin
TomKat11-Sep-04 3:21
TomKat11-Sep-04 3:21 
you have to know the parameters , declare the prototype and import function using loadlibrary and getprocaddress .


I am the MIGHTY KEEPER of the BOOK OF KNOWLEDGE . Contact me to get your copy .
GeneralRe: Yeah! are fun Pin
Abbas_Riazi11-Sep-04 10:23
professionalAbbas_Riazi11-Sep-04 10:23 
GeneralRe: Yeah! are fun Pin
Jigar Mehta7-Oct-04 18:43
Jigar Mehta7-Oct-04 18:43 
GeneralRe: Yeah! are fun Pin
RabidCow11-Sep-04 21:53
RabidCow11-Sep-04 21:53 
GeneralOOH! very good Pin
rambod soraty10-Sep-04 12:09
rambod soraty10-Sep-04 12:09 

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