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Hello World
Tutorial Series   Beginner Tutorial
Previous   C++, Qt, Building KDE
What's Next   Tutorial 2 - KXmlGuiWindow
Further Reading   CMake


Your first program shall greet the world with a friendly "Hello World", what else? For that, we will use a KMessageBox and customise one of the buttons.

Als je meer informatie wilt over een klasse die je tegenkomt, kun je de 'kde'-zoekmachine gebruiken. Om bijvoorbeeld meer te weten te komen over een KMessageBox, typ je "kde:kmessagebox" in Konqueror, rekonq of KRunner, waarna de documentatie verschijnt.

You might want to use KDevelop or QtCreator as IDE for your projects.

De code

All the code we need will be in one file, main.cpp. Create that file with the code below:

#include <QApplication>
#include <QCommandLineParser>
#include <KAboutData>
#include <KLocalizedString>
#include <KMessageBox>

int main (int argc, char *argv[])
    QApplication app(argc, argv);

    KAboutData aboutData(
                         // The program name used internally. (componentName)
                         // A displayable program name string. (displayName)
                         i18n("Tutorial 1"),
                         // The program version string. (version)
                         // Short description of what the app does. (shortDescription)
                         i18n("Displays a KMessageBox popup"),
                         // The license this code is released under
                         // Copyright Statement (copyrightStatement = QString())
                         i18n("(c) 2015"),
                         // Optional text shown in the About box.
                         // Can contain any information desired. (otherText)
                         i18n("Some text..."),
                         // The program homepage string. (homePageAddress = QString())
                         // The bug report email address
                         // (bugsEmailAddress = QLatin1String("[email protected]")
                         QStringLiteral("[email protected]"));
    aboutData.addAuthor(i18n("Name"), i18n("Task"), QStringLiteral("[email protected]"),
                         QStringLiteral(""), QStringLiteral("OSC Username"));

    QCommandLineParser parser;
    KGuiItem yesButton( i18n( "Hello" ), QString(),
                        i18n( "This is a tooltip" ),
                        i18n( "This is a WhatsThis help text." ) );

        (0, i18n( "Hello World" ), i18n( "Hello" ), yesButton ) 
        == KMessageBox::Yes? EXIT_SUCCESS: EXIT_FAILURE;

First we need to create a QApplication object. This needs to be done exactly once in each program since it is needed for things such as i18n. It also should be created before any other KDE Framework or Qt object. A call to KLocalizedString::setApplicationDomain() is required to properly set the translation catalog and must be done before the next step happens.

The first KDE Framework specific object we create in this program is KAboutData. This is the class used to store information about the program such as a short description, authors or license information. Pretty much every KDE application should use this class. We then call KAboutData::setApplicationData() to initialize the properties of the QApplication object.

Then we come to QCommandLineParser. This is the class one would use to specify command line switches to, for example, open the program with a specific file. However, in this tutorial, we simply initialise it with the KAboutData object we created so we can use the --version or --author switches.

We zijn nu klaar met alle nodige KDE-instellingen, en we kunnen verdergaan met interessantere dingen. We maken een popup, maar daarbij passen we één van de knoppen aan. Om deze wijziging aan te brengen, moeten we een KGuiItem-object gebruiken. Het eerste argument in de constructor van KGuiItem is de tekst die op het item komt te staan (in ons geval dus de knop). Dan hebben we een optie om een icoontje op de knop te zetten; dat willen we niet en dus geven we alleen een QString() mee. Dan stellen we de tooltip in (de tekst die verschijnt als je met de muis boven een item hangt) en ten slotte de "Wat is dit?"-tekst (die je krijgt door met de rechtermuisknop te klikken of op Shift-F1 te drukken).

Now we have our item, we can create our popup. We call the KMessageBox::questionYesNo() function which, by default, creates a message box with a "Yes" and a "No" button. The second argument is the text that will appear in the message box above the buttons. The third is the caption the window will have and finally, we set the KGuiItem for (what would normally be) the "Yes" button to the KGuiItem yesButton we created.

Note that all user-visible text is passed through the i18n() function; this is necessary for the UI to be translatable. More information on localization can be found in the localization tutorial.

We zijn klaar met de code; laten we het programma compileren en uitproberen.


You want to use CMake for your build environment. You provide a file CMakeLists.txt, CMake uses this file to generate all Makefiles out of it.


Create a file named CMakeLists.txt in the same directory as main.cpp with this content:

cmake_minimum_required(VERSION 3.0)

project (tutorial1)

set(QT_MIN_VERSION "5.3.0")
set(KF5_MIN_VERSION "5.2.0")

find_package(ECM 1.0.0 REQUIRED NO_MODULE)

include(KDECompilerSettings NO_POLICY_SCOPE)

# Find Qt modules
    Core    # QCommandLineParser, QStringLiteral
    Widgets # QApplication 

# Find KDE modules
    CoreAddons      # KAboutData
    I18n            # KLocalizedString
    WidgetsAddons   # KMessageBox

set(tutorial1_SRCS main.cpp)

add_executable(tutorial1 ${tutorial1_SRCS})



The find_package() function locates the package that you ask it for (in this case ECM, Qt5, or KF5) and sets some variables describing the location of the package's headers and libraries. ECM, or Extra CMake Modules, is required to import special CMake files and functions for building KDE applications.

Here we try to find the modules for Qt 5 and KDE Frameworks 5 required to build our tutorial. The necessary files are included by CMake so that the compiler can see them at build time. Minimum version numbers are set at the very top of CMakeLists.txt file for easier reference.

Daarna maken we een variabele tutorial1_SRCS met behulp van de functie set(). In dit geval stellen we de variabele in op de naam van ons enige bronbestand.

Then we use add_executable() to create an executable called tutorial1 from the source files listed in our tutorial1_SRCS variable. Afterwards, we link our executable to the necessary libraries using target_link_libraries() function. The line starting with install writes a default "install" target into the Makefile.

Make aanroepen en uitvoeren

To compile, link and install your program, you must have several software installed, e.g. cmake, make and gcc-c++, and the Qt 5 and KDE Frameworks development files. To be sure you have everything, best follow this install guide.

While you can run CMake directly inside the source code directory itself, it is a best practice, and actually enforced in some KDE software, to use a separate build directory and run CMake from there:

mkdir build && cd build

You can invoke CMake and make manually:

cmake .. && make

And launch it with:


De volgende stappen

Now you can move on to using KXmlGuiWindow.

This page was last edited on 19 July 2019, at 17:40. Content is available under Creative Commons License SA 4.0 unless otherwise noted.