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Posted 15 Dec 1999

Using one extension DLL in another

, 15 Dec 1999
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How to avoid link errors when using one MFC extension DLL from another
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If you create an extension DLL you can most conveniently export one or more of its classes using AFX_EXT_CLASS. However if you create a second extension DLL and try to use classes from the first you will run into a small problem.

The value of AFX_EXT_CLASS will cause your new DLL to try and export your dependent classes! You will get link errors such as below for the classes in the first DLL:

error LNK2001: unresolved external symbol ..........

What you need to do is temporarily re-define AFX_EXT_CLASS when you include the header files for the classes in the DLL you are importing classes from. The following example shows how to do this:

//change the definition of AFX_EXT... to make it import</P>

#undef AFX_EXT_API
#define AFX_EXT_API         AFX_API_IMPORT
//Include headers for the dll / lib that we use classes from

#include "DLLOne.H"
//put the values back to make AFX_EXT_CLASS export again

#undef AFX_EXT_API
#define AFX_EXT_API         AFX_API_EXPORT
//Include headers for the classes we are creating in this DLL

#include "DLLTwo.H"


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Randy More
United States United States
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Comments and Discussions

GeneralMy vote of 5 Pin
JasMineLeaf14-Oct-13 0:10
memberJasMineLeaf14-Oct-13 0:10 
QuestionBetter solution?!? Pin
Shinydooga15-May-03 6:54
sussShinydooga15-May-03 6:54 
AnswerRe: Better solution?!? Pin
quangtin328-Aug-07 19:12
memberquangtin328-Aug-07 19:12 
Generalbug Pin
Robit26-May-01 16:56
memberRobit26-May-01 16:56 

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