Using one extension DLL in another

WEBINAR: On-demand webcast

How to Boost Database Development Productivity on Linux, Docker, and Kubernetes with Microsoft SQL Server 2017 REGISTER >

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  • Your email address will not be published.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 software-defined data center (SDDC) and new trends in cloud and virtualization bring increased agility, automation, and intelligent services and management to all areas of the data center. Businesses can now more easily manage the entire lifecycle of their applications and services via the SDDC. This Aberdeen analyst report examines how a strong foundation in both the cloud and internal data centers is empowering organizations to fully leverage their IT infrastructure and is also preparing them to be able …

  • Whether a mandate to secure all web and mobile apps comes from a newly enlightened CIO or in response to a major security breach, beginning even a small application security program can be a daunting task. How will you know how many digital assets you have, let alone their risk profile? In this webinar we explore how, using a cloud solution like Fortify on Demand, even the largest organizations can begin to scan apps immediately and rapidly scale an application security program. Identify and risk rank assets, …

Most Popular Programming Stories

More for Developers

RSS Feeds

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