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Posted 30 Sep 2004

DLLs are Simple! Part 3

, 30 Sep 2004
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This article describes how to create a DLL with a DEF file and use it.


In the third part of the assortment of articles "DLLs are Simple!" I describe how to create a DLL using a DEF file. What is a DEF file? It is a module-definition (*.def) file that is a text file containing one or more module statements that describe various attributes of a DLL, including:

LIBRARY statement statement identifies the DEF file as belonging to a DLL
EXPORTS statement lists the names of the functions exported by the DLL
DESCRIPTION statement describes the purpose of the DLL (optional)
LIBRARY      "DefExported"
DESCRIPTION  'DefExported For Present in CodeProject'
   Multiply @1

How to Build a DLL Using a DEF File

  1. Run VC++.
  2. Choose File>New.
  3. In the dialog box, choose "MFC AppWizard (DLL)" and name it, e.g. DefExported.
  4. Declare a member function:
     int Multiply(int PartOne,int PartTwo);
  5. Then define it:
    int CDefExportedApp::Multiply(int PartOne, int PartTwo)
     return PartOne*PartTwo;
  6. In the FileView tab, click "Source Files" and double click on DefExported.def.
  7. After the EXPORT statement, enter [function name] @[number] like this:
    LIBRARY      "DefExported"
    DESCRIPTION  'DefExported For Present in CodeProject'
     ; Explicit exports can go here
     Multiply @1
  8. Click the Build Button.
  9. Bring the DLL out of the oven!!

How to Use a DLL

To use a DLL dynamically, there are three simple API functions:

  • LoadLibrary ( [path of DLL] ) Loads a DLL into the process address, returning a handle to the DLL.
  • GetProcAddress ( [loaded library] , [function name] )
    Returns a handle of a function so that it can be used in your application.
  • FreeLibrary( [handle of loaded DLL] )
    Releases the memory allocated when the DLL was loaded.
  1. Run VC++.
  2. Choose from the menu File>New.
  3. In the dialog box, choose "MFC AppWizard (EXE)" and name it, e.g. DynamicLoad.
  4. Select "Dialog Based" and click the Finish button.
  5. Place a button control on the dialog and double click on it to create its click event.
  6. Before typing the code for the button click (BN_CLICKED) event, we must define a new function pointer with the correct number of parameters. This is done according to the parameters of the function we exported above.
    typedef int (CALLBACK* LPFNMLTPLY)(int,<span lang="en-us"> int);<span lang="en-us">
    <p>Sometimes you have to convert some variable types. For more information about this conversion, see Microsoft Support Article ID: <a href=";en-us;117428">Q117428</a>. </p>
  7. Enter the code for the button click event:
    HINSTANCE hClcltr=LoadLibrary("DefExported.dll");
    LPFNMLTPLY lpfnMuliply;
    lpfnMuliply = (LPFNMLTPLY)GetProcAddress(hClcltr,"Multiply");
  8. Now we can use the Multiply function by calling lpfnMultiply and storing the return value.
  9. When you are finished using the library, you must call the FreeLibrary API to release the memory allocated from the LoadLibrary method.
    FreeLibrary( hClcltr );


  • 30 September, 2004 -- Original version posted


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.

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About the Author

Mahmoud Komeily
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

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Comments and Discussions

QuestionHow to pass dynamilly created object to dll? Pin
dufduf23-May-10 23:47
memberdufduf23-May-10 23:47 

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