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{{DISPLAYTITLE:Development/Tutorials/First program/KDE4}}<languages />

{{TutorialBrowser|

series=Beginner Tutorial|

name=Hello World|

pre=[http://mindview.net/Books/TICPP/ThinkingInCPP2e.html C++], [http://qt.nokia.com Qt], [[Getting_Started/Build|Building KDE]]|

next=[[Development/Tutorials/Using_KXmlGuiWindow/KDE4|Tutorial 2 - KXmlGuiWindow]]|

<div class="mw-translate-fuzzy">
reading=[[Development/Tutorials/CMake|CMake]]
}}
</div>

==Abstract==

Your first program shall greet the world with a friendly "Hello World", what else? For that, we will use a {{class|KMessageBox}} and customise one of the buttons.
[[image:introtokdetutorial1.png|frame|center]]

{{Tip|To get more information about any class you come across, you can use the ‘kde’ search engine. For example, to look for information about KMessageBox, just type "kde:kmessagebox" into Konqueror, Rekonq or KRunner, and you’ll be taken to the documentation.}}

{{Tip|
You might want to use [[qtcreator|QtCreator]] as IDE for your projects.
}}

{{Attention||The source code on this page applies only to the older KDE Development Platform 4 ("KDE 4"). For the current KDE Frameworks 5 ("KF5") version, see [[Special:myLanguage/Development/Tutorials/First_program]]}}

==The Code==

All the code we need will be in one file, <tt>main.cpp</tt>. Create that file with the code below:
<syntaxhighlight lang="cpp-qt">
#include <cstdlib>

#include <KApplication>
#include <KAboutData>
#include <KCmdLineArgs>
#include <KMessageBox>
#include <KLocale>

<div class="mw-translate-fuzzy">
int main (int argc, char *argv[])
{
    KAboutData aboutData(
                         // The program name used internally.
                         "tutorial1",
                         // The message catalog name
                         // If null, program name is used instead.
                         0,
                         // A displayable program name string.
                         ki18n("Tutorial 1"),
                         // The program version string.
                         "1.0",
                         // Short description of what the app does.
                         ki18n("Displays a KMessageBox popup"),
                         // The license this code is released under
                         KAboutData::License_GPL,
                         // Copyright Statement
                         ki18n("(c) 2007"),
                         // Optional text shown in the About box.
                         // Can contain any information desired.
                         ki18n("Some text..."),
                         // The program homepage string.
                         "http://example.com/",
                         // The bug report email address
                         "submit@bugs.kde.org");
</div>

<div class="mw-translate-fuzzy">
KCmdLineArgs::init( argc, argv, &aboutData );
    KApplication app;
    KGuiItem yesButton( i18n( "Hello" ), QString(),
                        i18n( "This is a tooltip" ),
                        i18n( "This is a WhatsThis help text." ) );
    return 
        KMessageBox ::questionYesNo 
        (0, i18n( "Hello World" ), i18n( "Hello" ), yesButton ) 
        == KMessageBox ::Yes? EXIT_SUCCESS: EXIT_FAILURE;
}
</syntaxhighlight>
The first KDE specific code we come across in this program is {{class|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.
</div>

Then we come to {{class|KCmdLineArgs}}. 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 {{class|KAboutData}} object we created so we can use the <tt>--version</tt> or <tt>--author</tt> switches.

Then we create a {{class|KApplication}} object. This needs to be done exactly once in each program since it is needed for things such as [[Development/Tutorials/Localization/i18n|i18n]].

Now we've done all the necessary KDE setup, we can move on to doing interesting things with our application. We're going to create a popup box but we're going to customise one of the buttons. To do this customisation, we need to use a {{class|KGuiItem}} object. The first argument in the {{class|KGuiItem}} constructor is the text that will appear on the item (in our case, a button). Then we have an option of setting an icon for the button but we don't want one so we just give it <tt>QString()</tt>. We then set the tooltip (what appears when you hover over an item) and finally the "What's This?" (accessed through right-clicking or Shift-F1) text.

Now we have our item, we can create our popup. We call the <tt>{{class|KMessageBox}}::questionYesNo()</tt> 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 <tt>KGuiItem yesButton</tt> 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 [[Development/Tutorials/Localization/i18n|localization tutorial]].

We're all done as far as the code is concerned. Now to build it and try it out.

== Build ==

You want to [[Development/Tutorials/CMake|use CMake]] for your build environment. You provide a file CMakeLists.txt, cmake uses this file to generate all Makefiles out of it.

=== CMakeLists.txt ===

Create a file named CMakeLists.txt in the same directory as main.cpp with this content:
<syntaxhighlight lang="cmake">
project (tutorial1)
find_package(KDE4 REQUIRED)
include (KDE4Defaults)
include_directories(${KDE4_INCLUDES})
set(tutorial1_SRCS main.cpp)
kde4_add_executable(tutorial1 ${tutorial1_SRCS})
target_link_libraries(tutorial1 ${KDE4_KDEUI_LIBS})
install(TARGETS tutorial1  ${INSTALL_TARGETS_DEFAULT_ARGS})
</syntaxhighlight>
The <tt>find_package()</tt> function locates the package that you ask it for (in this case KDE4) and sets some variables describing the location of the package's headers and libraries. In this case we will use the <tt>KDE4_INCLUDES</tt> variable which contains the path to the KDE4 header files.

In order to allow the compiler to find these files, we pass that variable to the <tt>include_directories()</tt> function which adds the KDE4 headers to the header search path.

Next we create a variable called <tt>tutorial1_SRCS</tt> using the <tt>set()</tt> function. In this case we simply set it to the name of our only source file.

Then we use <tt>kde4_add_executable()</tt> to create an executable called <tt>tutorial1</tt> from the source files listed in our <tt>tutorial1_SRCS</tt> variable. Afterwards, we link our executable to the KDE4 kdeui library using <tt>target_link_libraries()</tt> and the <tt>KDE4_KDEUI_LIBS</tt> variable which was set by the <tt>find_package()</tt> function. The line starting with <tt>install</tt> writes a default "install" target into the Makefile.

=== Make And Run ===

To compile, link and install your program, you must have several software installed, e.g. kdelibs, cmake, make and gcc-c++. To be sure you have everything, best follow [[Getting_Started/Build/Environment|this install guide]].

You can invoke CMake and make manually:
<syntaxhighlight lang="bash">
cmake . && make && make install
</syntaxhighlight>
Or, if you set up your environment as described in [[Getting_Started/Build/Environment|Getting Started/Build/Environment]], you can compile this code with:
<syntaxhighlight lang="bash">
cmakekde
</syntaxhighlight>

And launch it with:
<syntaxhighlight lang="bash">
./tutorial1
</syntaxhighlight>

==Moving On==

Now you can move on to [[Development/Tutorials/Using_KXmlGuiWindow/KDE4|using KXmlGuiWindow]].

[[Category:C++]]