An application sends an LB_ADDFILE message to add the specified filename to a list box that contains a directory listing.
LB_ADDFILE wParam = 0; // not used; must be zero lParam = (LPARAM) (LPCTSTR) lpszFilename; // name of file to add
The return value is the zero-based index of the file that was added, or LB_ERR if an error occurs.
The list box to which lpszFilename is added must have been filled by the DlgDirList function.