"File" > "New File or Project..." > "Application" > "Qt Widgets Application" generates a header file below when the option" C++" > "Qt Class Generation" > "Add Qt Version #ifdef for module names" is unchecked.

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtGui/QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

This doesn't compile because QMainWindow belongs QtWidgets module in Qt 5.

Qt Creator is shipped with Qt 5 now a days, can we change it #include <QtWidgets/QMainWindow> by default?
or can we simply remove QtGui/ from there?

https://qt.gitorious.org/qt-creator/qt-creator/source/2adc5c5dc63835644912e403690c230739c27316:src/plugins/designer/qtdesignerformclasscodegenerator.cpp#L131