In my programming, I realized I need to start polling SM_CXVIRTUALSCREEN rather than SM_CXSCREEN in order to support users with multiple monitors.
However, when I tried to GetSystemMetrics (SM_CYVIRTUALSCREEN)) I got a build error and took advice from the Web that I needed to add multimon.h to my code.
So I got that file and added it to my source folder, and added
at the top of the source file that includes the GetSystemMetrics call.
And I added multimon.h to the project using Project | Add To Project | Files .
However when I try to build I get
"error LNK2001: unresolved external symbol _xGetSystemMetrics@4"