Getting Started With Qt: How to Develop the First Program?

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The First Program in Qt

Qt is a powerful tool which has a variety of ways to implement a programmer’s ideas in life. Let’s start with the development of the first program.

So, we have a QtCreator development environment with the compiler connected to it (for example, MinGW). Select New Project -> Other Project -> Subdirs Project in the development environment.

Let’s create a QWidget project firstProgram and delete files mainwindows.h, mainwindows.cpp, and the form.

Write the code of the program which prints  “Hello World!” on the screen.

In main.cpp:

#include <QApplication>

#include <QHBoxLayout>

#include <QLabel>

#include <QPushButton>

int main(int argc, char *argv[])

{

   QApplication app(argc, argv);

   QHBoxLayout * layout = new QHBoxLayout;

   QLabel *label = new QLabel(“Hello!”);

   QPushButton *button = new QPushButton(“Exit”);

   QWidget *mainForm = new QWidget;

   QObject::connect(button,SIGNAL(clicked()),&app,SLOT(quit()));

   layout->addWidget(label);

   layout->addWidget(button);

   mainForm->setLayout(layout);

   mainForm->show();

   return app.exec();

}

Let’s look at the program code:

The lines 1-4 connect necessary header files. The family of classes <QWidget> is responsible for the GUI in the Qt. Since we need the widgets, the first thing we connect is the desired libraries (QLabel, QPushButton).

#include <QApplication>

QApplication app(argc, argv);

The self-titled class connected via QApplication header file is needed in any Qt-project in a single instance. It is responsible for the event tracking and messaging system, changing the appearance of the application windows, and other useful features.

QHBoxLayout * layout = new QHBoxLayout;

QLabel *label = new QLabel(“Hello World”);

QPushButton *button = new QPushButton(“Exit”);

QWidget *mainForm = new QWidget;

This part of the space for classes is reserved by a dynamic memory.

QObject::connect(button,SIGNAL(clicked()),&app,SLOT(quit()));

The signals and slots mechanism is implemented through a method of the QObjekt class. In this case, the clicked () signal is generated when you click the application button, which activates the quit () slot and closes the application.

layout->addWidget(label);

layout->addWidget(button);

For the location of widgets “on the grid” either horizontally or vertically we use QHBoxLayout, QGridLayout, and QHBoxLayout classes. Method addWidget adds them to the layout manager.

mainForm->setLayout(layout);

mainForm->show();

The last lines assign the layout class with its widgets to the window and make it visible.

As a result, you should get the program:

Thanks for your attention!

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