@suslucoder If you changed anything in ui_mainwindow.h this could happen. If you get what seems like an inexplicable error when compiling, wiping the output directory can sometimes resolve. However, this does not apply to normal, run-of-the-mill errors!

@Chris-Kawa Thank you, this solves the problem. As to alternative way to exit, I already have exit action on tray's menu. Have a nice day.

Hi and welcome to devnet, You have to give more information about your setup. What device are you going to use ? What version of Qt ? What Linux distribution ? What graphical backend ?

more cursors [EDIT: Irrelevant link removed --JKSH]

MainWindow can be a QMainWindow or a QWidget depending on what parameter you choose

Hi, Fortunately for you Qt is very intuitive that way : you just have to implement the resizeEvent method.