You can use QDesktopServices static method (Qt4):
QString path = QDesktopServices::storageLocation(QDesktopServices::DataLocation);
In Qt5:
QString path = QStandardPaths::standardLocations(QStandardPaths::DataLocation).at(0);
To get Roaming folder:
QSettings settings(QSettings::IniFormat, QSettings::UserScope, "AppName", "application");
QString location = QFileInfo(settings.fileName()).absolutePath() + "/";
In my case path was:
C:/Users/maxim.makhun/AppData/Roaming/AppName/