Qt 5.3. QtWidgets: No such file or directory #include <QtWidgets>

Question

I want to compile Qt example. I get error QtWidgets: No such file or directory #include

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets - does not help
QT += widgets                                   - does not help
INCLUDEPATH += /opt/Qt/5.3/Src/qtbase/include/  - does not help

Qt 5.3. Ubuntu 14.04 x64.

Answer 1

You need to double check that you completed all these steps:

• Module installed

• greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

• You re-run the Qt 5 qmake.

Having said that, I would like to remind you that including the whole module is not a good idea as it includes all the widgets related things. Try to narrow it down to the headers that you really need.

Answer 2

As you noticed Qt directory structure changed between Qt4 and Qt5. QWidget header moved to a QtWidgets directory. Try adding

INCLUDEPATH += /opt/Qt/5.3/Src/qtbase/include/QtWidgets

If that does not help try finding the header manually using

find /opt/Qt/5.3/Src/qtbase/ -name QWidget

and and the directory it is in to INCLUDEPATH

Edit based on comment from Final Contest.

I agree that workarounds usually are a bad idea. To test where QT your installation looks for qt5 headers and libraries. Create a minimal project.

#include <QApplication>
#include <QtWidgets>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QWidget w;
    w.show();
    app.exec();
}

Generate a project and add QT += widget

/opt/Qt/5.3/Src/qtbase/bin/qmake -project

Project file

######################################################################
# Automatically generated by qmake (3.0) Thu Jul 10 13:05:17 2014
######################################################################

TEMPLATE = app
TARGET = so_qtwidgets
INCLUDEPATH += .

QT += widgets

# Input
SOURCES += main.cpp

Generate a make file

/opt/Qt/5.3/Src/qtbase/bin/qmake

The interesting parts widget flag adds:

• In my case -I/usr/include/qt5/QtWidgets -I/usr/include/qt5/QtGui to INCPATH
• -DQT_WIDGETS_LIB to DEFINES variable.
• -lQt5Widgets -lQt5Gui to libs.

The only part which should differ is the paths to QtWidgets and QtGui. If these a wrong the I would try reinstalling Qt.

Answer 3

Check what your .pro file looks like before you run "make". I found that the command "qmake -project" auto generated a .pro file that caused this same error. I now compiled my qt project via the following commands and the error went away:

qmake my_project.pro
make