QPixmap documentation stil references QPixmap::toWinHICON() and QPixMap::fromWinHICON():

The QPixmap class also supports conversion to and from HICON: the toWinHICON() function creates a HICON equivalent to the QPixmap, and returns the HICON handle. The fromWinHICON() function returns a QPixmap that is equivalent to the given icon.

However, these functions were removed in Qt 5 and replaced in Qt 5.2.0 by QtWin::fromHICON() and QtWin::toHICON() (QTBUG-27103).