EN_HSCROLL
idEditControl = LOWORD(wParam);
hwndEditControl = (HWND)lParam;
The EN_HSCROLL notification message is sent when the user clicks an edit control's horizontal scroll bar. The control's parent window receives this notification message through a WM_COMMAND message. The parent window is notified before the screen is updated.
idEditControl
Value of low word of wParam. Specifies the edit-control ID.
hwndEditControl
Value of lParam. Specifies the edit-control window handle.
WM_COMMAND