LB_SETSEL Overview Group

An application sends an LB_SETSEL message to select a string in a multiple-selection list box.

LB_SETSEL 

wParam = (WPARAM) (BOOL) fSelect;   // selection flag 

lParam = (LPARAM) (UINT) index;     // item index

Parameters

fSelect: Value of wParam. Specifies how to set the selection. If the fSelect parameter is TRUE, the string is selected and highlighted; if fSelect is FALSE, the highlight is removed and the string is no longer selected.
index: Value of lParam. Specifies the zero-based index of the string to set. If index is -1, the selection is added to or removed from all strings, depending on the value of fSelect.

If an error occurs, the return value is LB_ERR.

Use this message only with multiple-selection list boxes.