/home/idiao123/ceshi/mainwindow.h:17:error:'nullptr'wasnotdeclaredinthisscopeexplicitMainWindow(QWidget*parent=nullptr);^/home/idiao123/ceshi/main.cpp:-1:Infunction'intmain(

/home/idiao123/ceshi/mainwindow.cpp:17:error:'open_buzzer'wasnotdeclaredinthisscopeopen_buzzer();^/home/idiao123/ceshi/mainwindow.cpp:21:error:'close_buzzer'wasnotdeclaredinthisscopeclose_