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  • Your email address will not be published.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

  • The open source cloud computing project OpenStack has come a long way since NASA and Rackspace launched it in 2010. Backed by leading technology infrastructure providers including Cisco, Dell, EMC, HP, IBM, Intel, and VMware, OpenStack underpins significant workloads at an increasingly diverse set of organizations, including BWM, CERN, Comcast, eBay, and Wal-Mart. For CIOs engaged in broader programs to win, serve, and retain customers -- and refocus business technology (BT) spend -- a planned and pragmatic …

  • Microsoft® Office 365 is a top choice for enterprises that want a cloud–based suite of productivity collaboration applications. With Office 365, you get access to Microsoft™ Office solutions practically anytime, anywhere, on virtually any device. It's a great option for current Microsoft users who can now build on their experience with Microsoft™ solutions while enjoying the flexibility of a cloud-based delivery. But even organizations with no previous investment in Microsoft will find that …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date