Using one extension DLL in another

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
#undef AFX_EXT_CLASS
#undef AFX_EXT_API
#undef AFX_EXT_DATA
#define AFX_EXT_CLASS AFX_CLASS_IMPORT
#define AFX_EXT_API AFX_API_IMPORT
#define AFX_EXT_DATA AFX_DATA_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_CLASS
#undef AFX_EXT_API
#undef AFX_EXT_DATA
#define AFX_EXT_CLASS AFX_CLASS_EXPORT
#define AFX_EXT_API AFX_API_EXPORT
#define AFX_EXT_DATA AFX_DATA_EXPORT

//Include headers for the classes we are creating in this DLL
#include "DLLTwo.H"

Posted: March, 8, 98



Comments

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Live Event Date: August 13, 2014 @ 1:00 p.m. ET / 10:00 a.m. PT If you are developing applications, you'll want to join us to learn how applications are changing as a result of gesture recognition. This technology will change how you and your users interact - not simply with your devices, but with the world around you. Your devices will be able to see and hear what your users are doing. Are your applications ready for this? Join us to learn about Intel® RealSense™ Technology, including never been …

  • Intelligent N+X Redundancy, Placement Affinities, & Future Proofing in the Virtualized Data Center Virtualization brought about the ability to simplify business continuity management in IT. Workload portability and data replication capabilities mean that physical infrastructure failures no longer need impact application services, and they can rapidly be recovered even in the event of complete site failure. However, Enterprises and Service Providers face new challenges ensuring they have enough compute …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds