Following example from this link: http://developer.kde.org/documentation/books/kde-2.0-development/ch03lev1sec3.html
#include
#include
Maybe too late but... Had the same issue and fighted for a while to find where it comes from.
Right click on your project and select “Run qmake” to for a new build of MOC classes. It usually does run automatically...
The moc compiler generates the stubs and calls in moc_xxxx.cpp, and generates the vtable stuff