void SetHorizontalExtent( int cxExtent );
cxExtent
Specifies the number of pixels by which the list box can be scrolled horizontally.
Sets the width, in pixels, by which a list box can be scrolled horizontally. If the size of the list box is smaller than this value, the horizontal scroll bar will horizontally scroll items in the list box. If the list box is as large or larger than this value, the horizontal scroll bar is hidden.
To respond to a call to SetHorizontalExtent, the list box must have been defined with the WS_HSCROLL style.
CListBox::GetHorizontalExtent, LB_SETHORIZONTALEXTENT