Detect platform where my QT4 program is running on

[the_bis]

How can I detect if my QT4 program is running under Linux or under a Windows platform?

I have to differentiate some QFileDialog pre-settings.

Thank you,
the_bis

[jpn]

Q_WS_WIN (http://doc.trolltech.com/latest/qtglobal.html#Q_WS_WIN)
Q_WS_X11 (http://doc.trolltech.com/latest/qtglobal.html#Q_WS_X11)