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function TForm1.SaveAsExcelFile(AGrid: TStringGrid; AFileName: string): Boolean;
const
  {$J+} CXlsBof: array[0..5] of Word = ($809, 8, 00, $10, 0, 0); {$J-}
  CXlsEof: array[0..1] of Word = ($0A, 00);
var
  FStream: TFileStream;
  I, J: Integer;
begin
  Result := False;
  FStream := TFileStream.Create(PChar(AFileName), fmCreate or fmOpenWrite);
  try
    CXlsBof[4] := 0;
    FStream.WriteBuffer(CXlsBof, SizeOf(CXlsBof));
    for i := 0 to AGrid.ColCount - 1 do
      for j := 0 to AGrid.RowCount - 1 do
        XlsWriteCellLabel(FStream, I, J, AGrid.cells[i, j]);
    FStream.WriteBuffer(CXlsEof, SizeOf(CXlsEof));
    Result := True;
  finally
    FStream.Free;
  end;
end;                    

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XlsWriteCellLabel(FStream, I, J, AGrid.cells[i, j])                    

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procedure TForm1.XlsWriteCellLabel(XlsStream: TStream; const ACol, ARow: Word;
  const AValue: string);
var
  L: Word;
const
  {$J+}
  CXlsLabel: array[0..5] of Word = ($204, 0, 0, 0, 0, 0);
  {$J-}
begin
  L := Length(AValue);
  CXlsLabel[1] := 8 + L;
  CXlsLabel[2] := ARow;
  CXlsLabel[3] := ACol;
  CXlsLabel[5] := L;
  XlsStream.WriteBuffer(CXlsLabel, SizeOf(CXlsLabel));
  XlsStream.WriteBuffer(Pointer(AnsiString(AValue))^, L);
end;