An application sends the CB_SETDROPPEDWIDTH message to set the maximum allowable width, in pixels, of the list box of a combo box with the CBS_DROPDOWN or CBS_DROPDOWNLIST style.
CB_SETDROPPEDWIDTH
wParam = (WPARAM) wWidth, // width of list box, in pixels
lParam = 0, // not used, must be zero
If the message is successful, The return value is the new width of the list box.
If the message fails, the return value is CB_ERR.
By default, the minimum allowable width of the drop-zdown list box is 0. The width of the list box is either the minimum allowable width or the combo box width, whichever is larger.
Windows NT: Requires version 4.0 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Combo Boxes Overview, Combo Box Messages, CB_GETDROPPEDWIDTH