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;