LB_RESETCONTENT
wParam = 0; /* not used, must be zero */
lParam = 0L; /* not used, must be zero */An application sends an LB_RESETCONTENT message to remove all items from a list box.
This message has no parameters.
This message does not return a value.
If the list box was created with an owner-drawn style but without the LBS_HASSTRINGS style, the owner of the list box receives a WM_DELETEITEM message for each item in the list box.
This example removes all items from a list box:
SendDlgItemMessage(hdlg, ID_MYLISTBOX, LB_RESETCONTENT, 0, 0L);