Why don't you cast the pScrollBar parameter pass with the OnHScroll to CSliderctrl.. void OnHScroll(UINT nSBCode, UINT nPos, CScrollBar *pScrollBar) { // TODO: Add your message handler code here and/or call default int nControl=pScrollBar->GetDlgCtrlID(); CSliderCtrl* pControl= static_cast(GetDlgItem(nControl)); switch (nControl) { case IDC_SLD_CTRL: { }. . . . .