My app needs root privileges for some actions.
How is it possible to open upp kdesu when the app start and afterwards the app should continue running as root?
No, lets say that your app is known as myapp. Then create your application and name the binary myapp.real, then use a shell (bash) script called myapp to start myapp.real using kdesu.
If you want to circumvent the shell script, here is another way:
Create two applications. The first one being a wrapper application which will start a QPorcess. The QProcess is passed kdesu and the name of your real application as parameters.
There are 10 types of people in the world. Those that understand binary numbers and those that don't.