Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure TfrmMain.Memo1Click(Sender: TObject);
 var
   Line: Integer;
 begin
   with (Sender as TMemo) do
   begin
     Line      := Perform(EM_LINEFROMCHAR, SelStart, 0);
     SelStart  := Perform(EM_LINEINDEX, Line, 0);
     SelLength := Length(Lines[Line]);
   end;
 end;