Qt menuBar() Error

Question

I'm in the process of learning Qt4 and working through their tutorials.

In this tutorial:

http://doc.trolltech.com/4.5/mainwindows-menus-mainwindow-cpp.html

they have the following code:

fileMenu = menuBar()->addMenu(tr("&File"));

which causes the compiler to throw this error

g++ -c -pipe -O2 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -I. -o main.o main.cpp
g++ -c -pipe -O2 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -I. -o MainWindow.o MainWindow.cpp
MainWindow.cpp: In member function ‘void MainWindow::createMenus()’:
MainWindow.cpp:56: error: ‘((MainWindow*)this)->MainWindow::menuBar’ cannot be used as a function
MainWindow.cpp:61: error: ‘((MainWindow*)this)->MainWindow::menuBar’ cannot be used as a function
make: *** [MainWindow.o] Error 1

Does anyone know how I can fix this?

[Edit] Added full error Message with g++

Answer 1

Are you sure you're inheriting from QMainWindow, you haven't created or inherited any fields which might shadow the name menuBar, and you've run moc (or had qmake do so for you)?

The mainwindow.cpp, mainwindow.h, main.cpp, and menus.pro from the example, unmodified, should work fine.

$ cd examples/mainwindows/menus/
$ ls
main.cpp  mainwindow.cpp  mainwindow.h  menus.pro
$ qmake
$ make
g++ -c -pipe -g -O2 -mtune=native -pipe -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -o mainwindow.o mainwindow.cpp
g++ -c -pipe -g -O2 -mtune=native -pipe -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -o main.o main.cpp
/usr/bin/moc -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. mainwindow.h -o moc_mainwindow.cpp
g++ -c -pipe -g -O2 -mtune=native -pipe -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -o moc_mainwindow.o moc_mainwindow.cpp
g++ -Wl,--as-needed -Wl,--hash-style=both -o menus mainwindow.o main.o moc_mainwindow.o    -L/usr/lib64/qt4 -lQtGui -L/usr/lib64 -L/usr/lib64/qt4 -L/usr/X11R6/lib64 -pthread -lpng -lfreetype -lgobject-2.0 -lSM -lICE -pthread -pthread -lXrender -lXrandr -lXinerama -lfontconfig -lXext -lX11 -lQtCore -lz -lm -pthread -lgthread-2.0 -lrt -lglib-2.0 -ldl -lpthread
$ ls -F
Makefile  main.o          mainwindow.h  menus*     moc_mainwindow.cpp
main.cpp  mainwindow.cpp  mainwindow.o  menus.pro  moc_mainwindow.o

Answer 2

For some reason QMainWindow was not getting setting up correctly. This was fixed by calling the base class constructor.