Qt - QWidget: Cannot create a QWidget when no GUI is being used - c++

Question

I'm trying to run a simple Qt program, and when doing so, I get a console window mentioning: QWidget: Cannot create a QWidget when no GUI is being used, and the second line This application has requested the Runtime to terminate....., and the .exe file thus stops working.
My .pro file looks as follows:
#-------------------------------------------------
#
# Project created by QtCreator 2011-04-02T07:38:50
#
#-------------------------------------------------
QT += core
QT += gui
TARGET = Hello
CONFIG += console
CONFIG += qt
CONFIG -= app_bundle
TEMPLATE = app
SOURCES += main.cpp
Any ideas on that?
Thanks.

Answer 1

The problem is not with this .pro; it is most likely in main.cpp. Qt requires you to create a QApplication before creating any QWidget subclasses (as well as certain other classes, such as QPixmap). Your main function should begin with the line:
QApplication app(argc, argv);
and will probably end with a line like:
return app.exec();
In between these calls, you should create and show your main window.

Answer 2

I found that you can do it with a Qt Console project, but ofcourse it will not have the functionality of a console program when you are done with my edits.
First of all you need to exchange #include <QtCoreApplication> with #include <QApplication> in your main.cpp (where you start your application)
In the main(int,char**){
exchange QCoreApplication a(argc, argv); with QApplication a(argc, argv);
and in between QApplication and return a.exec you have your widget and other gui related stuff
and in the end you use return a.exec();}

Answer 3

I think I found where the issue is.
Since I'm using Qt Creator, and when creating a new project, I was choosing Qt Console Application instead of Qt Gui Application.

Answer 4

"QWidget: Cannot create a QWidget when no GUI is being used" happens when you application isn't QApplication instance.
From Qt docs:
QApplication specializes QGuiApplication with some functionality
needed for QWidget-based applications. It handles widget specific
initialization, finalization, and provides session management.
For any GUI application using Qt, there is precisely one QApplication
object, no matter whether the application has 0, 1, 2 or more windows
at any given time. For non-QWidget based Qt applications, use
QGuiApplication instead, as it does not depend on the QtWidgets
library.

Answer 5

From the docs,
the QApplication class manages the GUI application's control flow and main settings whilst
the QCoreApplication class provides an event loop for console Qt applications
I had the same problem, the default QT Console App uses the QCoreApplication instead of the QApplication to run the application.
Here is what i did to make it work
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget widget;
widget.show();
return a.exec();
}
And i did not change anything in my project file
QT += core
QT += gui
TARGET = Layouts
CONFIG += gui
CONFIG -= app_bundle
TEMPLATE = app
SOURCES += main.cpp