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<FONT COLOR="#AOAO99">Using one extension DLL in another</FONT></H3></CENTER>
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This code was contributed by <A HREF="mailto:rmore@cri.com">Randy More</A>.


<P><FONT>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.</FONT></P>

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

<P><FONT COLOR="#990000">error LNK2001: unresolved external
symbol ..........</FONT></P>

<P><FONT>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:</FONT></P>

<P><FONT COLOR="#990000">//change the definition of AFX_EXT... to
make it import<BR>

#undef AFX_EXT_CLASS<BR>

#undef AFX_EXT_API<BR>

#undef AFX_EXT_DATA<BR>

#define AFX_EXT_CLASS       AFX_CLASS_IMPORT<BR>

#define AFX_EXT_API         AFX_API_IMPORT<BR>

#define AFX_EXT_DATA        AFX_DATA_IMPORT</FONT></P>

<P><FONT COLOR="#990000">//Include headers for the dll / lib that we
use classes from<BR>

#include "DLLOne.H"</FONT></P>

<P><FONT COLOR="#990000">//put the values back to make AFX_EXT_CLASS
export again<BR>

#undef AFX_EXT_CLASS<BR>

#undef AFX_EXT_API<BR>

#undef AFX_EXT_DATA<BR>

#define AFX_EXT_CLASS       AFX_CLASS_EXPORT<BR>

#define AFX_EXT_API         AFX_API_EXPORT<BR>

#define AFX_EXT_DATA        AFX_DATA_EXPORT</FONT></P>

<P><FONT COLOR="#990000">//Include headers for the classes we are
creating in this DLL<BR>

#include "DLLTwo.H"</FONT></P>






<P>Posted: March, 8, 98


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