The EN_HSCROLL notification message is sent when the user clicks an edit control’s horizontal scroll bar. The parent window of the edit control receives this notification message through the WM_COMMAND message. The parent window is notified before the screen is updated.
EN_HSCROLL idEditCtrl = (int) LOWORD(wParam); // identifier of edit control hwndEditCtrl = (HWND) lParam; // handle of edit control