When I reached the step "You can now compile the project quadwild/quadwild.pro with qmake or QtCreator," I first used qmake and then make. However, I encountered numerous "undefined reference to" errors. Why did this happen? I would appreciate an explanation. Thank you.

When I reached the step "You can now compile the project quadwild/quadwild.pro with qmake or QtCreator," I first used qmake and then make. However, I encountered numerous "undefined reference to" errors. Why did this happen? I would appreciate an explanation. Thank you.