const 
  anzahl = 12; 
  datei = 'C:\TEST.TXT'; 
  a: array[0..anzahl - 1] of byte = (68, 66, 82, 46, 83, 111, 102, 116, 119, 
    97, 114, 101); 
var 
  f: file of byte; 
  s: string; 
 
procedure TForm1.FormCreate(Sender: TObject); 
begin 
  assignfile(f, datei); 
end; 
 
function bytesschreiben: boolean; 
var 
  x: byte; 
begin 
  result := false; 
{$I-} 
  reset(f); 
  if ioresult = 0 then begin 
    try 
      seek(f, filesize(f)); 
      for x := 0 to anzahl - 1 do write(f, a[x]); 
      result := true; 
    finally 
      closefile(f); 
    end; 
  end; 
{$I+} 
end; 
 
function byteslesen: boolean; 
var x: byte; 
begin 
  result := false; 
{$I-} 
  fillchar(a, sizeof(a), 0); 
  reset(f); 
  if ioresult = 0 then begin 
    try 
      if filesize(f) >= anzahl then begin 
        seek(f, filesize(f) - anzahl); 
        for x := 0 to anzahl - 1 do read(f, a[x]); 
        result := true; 
      end; 
    finally 
      closefile(f); 
    end; 
  end; 
{$I+} 
end; 
 
function bytesabschneiden: boolean; 
begin 
  result := false; 
{$I-} 
  reset(f); 
  if ioresult = 0 then begin 
    try 
      if filesize(f) >= anzahl then begin 
        seek(f, filesize(f) - anzahl); 
        truncate(f); 
        result := true; 
      end; 
    finally 
      closefile(f); 
    end; 
  end; 
{$I+} 
end; 
 
procedure TForm1.Button5Click(Sender: TObject); 
begin 
  if not bytesschreiben then s := 'FEHLER' 
  else s := 'O.K.'; 
  showmessage(s); 
end; 
 
procedure TForm1.Button6Click(Sender: TObject); 
var x: integer; 
begin 
  if not byteslesen then s := 'FEHLER' else 
  begin 
    s := ''; 
    for x := 0 to anzahl - 1 do s := s + char(a[x]); // z.B. 
  end; 
  showmessage(s); 
end; 
 
procedure TForm1.Button7Click(Sender: TObject); 
begin 
  if not bytesabschneiden then s := 'FEHLER' 
  else s := 'O.K.'; 
  showmessage(s); 
end;