LB_SETCOLUMNWIDTH
wParam = (WPARAM) cxColumn; /* column width */
lParam = 0L; /* not used, must be zero */
An application sends an LB_SETCOLUMNWIDTH message to a multiple-column list box (created with the LBS_MULTICOLUMN style) to set the width, in pixels, of all columns in the list box.
cxColumn
Value of wParam. Specifies the width, in pixels, of all columns.
This message does not return a value.
This example sets the width of the columns in a multiple-column list box:
WPARAM wColWidth;
wColWidth = 100; /* set column width to 100 pixels */
SendDlgItemMessage(hDlg, ID_MYLISTBOX, LB_SETCOLUMNWIDTH,
wColWidth, 0L);