Qt5 Tutorial Hello World - 2020

According to qt-project.org, Qt Quick is now in the center of Qt.

For changes in Qt5, please visit
QtDoc 5 C++ API changes..

Since the documentation and manuals of Qt (including the ones from the Qt communities) are superb, I've been wondering if there is any need of additional tutorial.

However, Qt's been growing for quite a long time, and it become huge in terms of materials to master and hard to keep up with the pace. So, my excuse for this tutorial is "We (may) need Qt Express!"

Most of the materials of this tutorial is extremely simple but eventually covers lots of topics with core samples (I admit I've just started, and it's just beginning of a long Journey).

I believe, in that way, we can taste variety of features that Qt provides without giving up in despair.

Qt Express!

Video recording - Producer and Consumer model using QSemaphore, for more info, please visit:

QSemaphores - Producer and Consumer.

We're using Qt 5.1 and QtCreator2.7.2 IDE:

In this tutorial, we will print out simple text "Hello World".

File->New File or Project...

Applications->Qt Console Application->Choose...

Let's see the main.cpp file that Creator made for us:

#include <QCoreApplication>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    
    return a.exec();
}

The QCoreApplication class provides an event loop for console Qt applications. This class is used by non-GUI applications to provide their event loop. For non-GUI application that uses Qt, there should be exactly one QCoreApplication object. For GUI applications, we will use QApplication.

When calling a.exec() the event loop is launched.

Let's compile this application. By clicking on the green arrow on the bottom left, Qt Creator will compile and execute it. And what happened ? The application seems to be launched and not responding. It is actually normal. The event loop is running and waiting for events such as mouse click, but we did not provide any event to be processed, so it will run indefinitely.

When we compile the project, behind the scene, our Qt app is compiled in the following steps:

1. qmake parses the .pro file, and generates makefile.
2. The program is build using make (jom on windows).

Let's print out "Hello World"i by modifying the source:

#include <QCoreApplication>
#include <QDebug>
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    
    qDebug() << "Hello World";

    return a.exec();
}

If we run the code again, it prints out "Hello World".