error C2027: use of undefined type 'QMenuBar'

[CroCo]

I'm reading a book in which there is a code as follows:

void MainWindow::createMenus()
{
	fileMenu = menuBar()->addMenu(tr("&File"));
	fileMenu->addAction(newAction);
	fileMenu->addAction(openAction);
...

fileMenu is defined as QMenu *fileMenu;. I'm getting the following error

mainwindow.cpp
.\mainwindow.cpp(196): error C2027: use of undefined type 'QMenuBar'
c:\qt\5.9.1\msvc2015\include\qtwidgets\qmainwindow.h(54): note: see declaration of 'QMenuBar'

I've taken a look at menuBar() in the QMainWindow class which is defined as QMenuBar * menuBar() const. Does that mean the code is old? Is there any change has been made for menuBar() from Qt4 to Qt5? Do I need to change the code to make it run? I'm Using Qt 5.9 with Visual Studio 2014. The author uses Qt 4.

[aha_1980]

Hi @CroCo,

http://doc.qt.io/qt-5/qmenubar.html :

Header: #include <QMenuBar>

have you done this?

Regards

[CroCo]

@aha_1980 said in error C2027: use of undefined type 'QMenuBar':

#include <QMenuBar>

that solved the problem. Thanks. How come a QMenu object is treated as a QMenuBar object?

[aha_1980]

@CroCo

I guess because here you use QMenuBar:

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

[CroCo]

@aha_1980 No fileMenu is QMenu pointer whereas the static function menuBar() returns a const QMenuBar pointer. I didn't do any casting.

[aha_1980]

@CroCo said in error C2027: use of undefined type 'QMenuBar':

whereas the static function menuBar() returns a const QMenuBar pointer.

That's what I said.

[CroCo]

@aha_1980 I'm sorry I didn't get it. Could you please elaborate a bit.

[mrjj]

Hi
it works because you assign the return of menuBar()->addMenu function call.
QMenu *addMenu(const QString &title);

[aha_1980]

@CroCo

You already answered you question yourself. You have a QMenuBar *menuBar pointer that you want to de-reference. The compiler cannot do it if the declaration of QMenuBar is unknown.

Therefore you have to add the #include <QMenuBar> before de-referencing. Ok?

[CroCo]

@aha_1980 thank you. it is clear.