Q: class in a DLL

Posted on 1998-09-13
Last Modified: 2013-11-20
How do I make a dll with a class in it that I can access in another MFC app?  I have been using _declspec(dllexport) and (dllimport) but for some reason when I link the project to test the class, it has unresolved externals to the imported (from the dll) class's functions.

How to I get a memory pointer to the class (that resides in the dll) so I can use class whatever in my test application?

Question by:brosoft
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Author Comment

ID: 1322113
PS. I would love some project code for making a DLL with a class and then accessing it from another project with LoadLibrary() etc...  Thanks again.

Accepted Solution

fjsen earned 100 total points
ID: 1322114
Try linking with the .lib file generated by the first application.



Author Comment

ID: 1322115
If I link with the .lib, what is the point of having a dll?
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Expert Comment

ID: 1322116
If you change the DLL code without change the interface, you don't need to recompile the client project.



Expert Comment

ID: 1322117
Use that dll as extension dll and export the class in this way.

class AFX_EXT_CLASS CMyClass : public CDialog


, then link this .lib with that calling application. then compile the application.
U won't get any errors.

Author Comment

ID: 1322118
So what is the point of a dll then?  If I just have to link the lib, then having a DLL is pointless.  I could just use a .lib file instead and statically link it to every file that I compile that needs the dll.  

I am trying to cut down on repetitive code and use one dll for all my programs to use the common functions.  Just using a lib would make it pointless... :(


Expert Comment

ID: 1322119
When creating a dll you will get a lib as well. This lib will hold the code to use the dll. Once you have linked your MFC app with this library who will be able to change the code of your dll without linking your app again. The only thing you have to keep in mind is that the names of the entry points, such as your class and its methods, should not be changed.

Author Comment

ID: 1322120
thanks, I figured it out.  Explicit DLL's are what we are talking about here, linking with the .lib and all that.

Implicit ones are the one's I wanted.  Where you grab a ptr to the function or class and then don't have to link with the .lib.


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