Error

[TheChapu]

[AndyTsangChun]

I got exactly the same error on Ubuntu 16.04, have u figure out how to solve it yet??

I tried the
#include <QApplication>
and
QT += widgets
seems not working, btw the widget one was actually already there

======================================================
Solution found here

sudo apt-get remove --purge qt4-default qt4-designer qt4-dev-tools qt4-qmake qt4-doc qt4-linguist-tools qtchooser
sudo apt-get install qt5-qmake qt5-default qttools5-dev-tools libqt5script5 libqt5scripttools5 qtscript5-dev

[hanshan1]

the same error

[dmitriy-nz]

Solution for me:

qmake --version
QMake version 3.0
Using Qt version 5.5.1 in /usr/lib/x86_64-linux-gnu

1. Delete #include <QtGui> from about.cpp
2. Add find_package(Qt5Gui) to file CMakeLists.txt after line find_package(Qt5Widgets)