How to Compile Qt Programs on Command line

Qt is a cross-platform application framework (toolkit) that is widely used for developing GUI applications, and also for developing non-GUI programs such as command-line tools and consoles for servers.

Qt is the underlying library in KDE and all the KDE specific applications. Qt allows you to create robust, well designed, GUI applications in the shortest period of time.

The advantages of Qt

• Cross platform support
• Free if you are creating GPLed applications.
• Relatively less complex when compared to other libraries in the same genre.
• A unique way of communication between user interfaces using Signal - Slot mechanism.
• A rich collection of ready made widgets that reduce the development time drastically.
• A choice of Free IDEs that help you speed up the designing of your applications.

A collection of Free IDEs for Qt development is listed at the end of this article.

How to create a Qt project

Here is a cool method of creating a Qt project from a terminal.

The code shown below is a simple C++ program that will display a label with the words "Linux is wonderful" inside its own window. If you want to try it out, copy the code shown below into a text editor and save it as test.cpp. You can give it any name.

#include 
#include 

int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QLabel *label = new QLabel("Linux is wonderful", 0);
app.setMainWidget(label);
label->show();
return app.exec();
}

The .cpp extension of the file name "test.cpp" tells us that it is a C++ file. For the uninitiated, in Linux, C++ programs are normally compiled using g++ compiler. If you don't have g++ compiler already installed, now is the right time to do so by installing the build-essential package which installs all the necessary compiler tools.

Usually, you use a file by name MakeFile which directs the compiler to compile your programs. And all you have to do is move into the directory containing the 'MakeFile' and your program, and run make.

So to compile the above program, you have to create a MakeFile first.

Generating a MakeFile

Qt has a easy way of generating a MakeFile. Here is how you do it.

Step 1: Move into the directory containing your code - in our case it is the file test.cpp.

Step 2: While in this directory, create a Qt project by running the following command -

$ qmake -project

This will create a project file called test.pro and include our program test.cpp into it.

Step 3: Now run qmake on the project file to create a platform specific MakeFile as follows -

$ qmake test.pro

At this stage if you do a listing of the contents of the directory, you will find a file by name MakeFile .

Compile the Qt program

To compile our program, it is now as simple as running make.

$ make

Executing your compiled program

After running make, you will find a executable file by name test in your directory which when run will display the label in a window.

$ ./test

This is one way of compiling a simple Qt project. For complex projects, you usually use specialised editors like those listed above which automates the creation of the project and the compilation.

Additional Resources

Qt Homepage - http://qt.digia.com/
Qt Creator - http://qt.digia.com/Product/Developer-Tools/
KDevelop - http://www.kdevelop.org/
Kommander - http://www.kde.org/applications/development/kommander/