Saving fpspreadsheet to file causes an error
lazarus / 49-FPSpreadsheet

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JD · 2012-09-29 12:31

Hi there everyone,

After the recent changes to the FPC 2.6.1 compiler, the internal
compiler error seems to have disappeared (for good, I hope  )

However, there seems to be a bug in the
TsSpreadBIFF8Writer.WriteToFile procedure in the xlsbiff8.pas file
used to create Excel 2003 files.

A error occurs on the line 'MemStream.Free' as seen in the code
snippet below. The Excel file is created in spite of the error but I
find it a little bothersome because it confuses the users of my
application.

The error goes away once I commented out this line. But this means
MemStream is created but not freed. Is this not a potential memory
leak notwithstanding the fact that MemStream is reassigned to
OleDocument.Stream?

Code: [Select]{*******************************************************
************
*  TsSpreadBIFF8Writer.WriteToFile ()
*
*  DESCRIPTION:    Writes an Excel BIFF8 file to the disc
*
*                  The BIFF 8 writer overrides this method because
*                  BIFF 8 is written as an OLE document, and our
*                  current OLE document writing method involves:
*
*                  1 - Writing the BIFF data to a memory stream
*
*                  2 - Write the memory stream data to disk using
*                      COM functions
*
*******************************************************************}
procedure TsSpreadBIFF8Writer.WriteToFile(const AFileName: string;
  AData: TsWorkbook; const AOverwriteExisting: Boolean);
var
  MemStream: TMemoryStream;
  OutputStorage: TOLEStorage;
  OLEDocument: TOLEDocument;
begin
  MemStream := TMemoryStream.Create;
  OutputStorage := TOLEStorage.Create;
  try
    WriteToStream(MemStream, AData);

    // Only one stream is necessary for any number of worksheets
    OLEDocument.Stream := MemStream;

    OutputStorage.WriteOLEFile(AFileName, OLEDocument,
AOverwriteExisting, 'Workbook');
  finally
    //MemStream.Free;               <======= Commented out by JD a
potential memory leak ?
    OutputStorage.Free;
  end;
end;

Any thoughts, suggestions?

JD

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taazz · 2012-09-29 12:43

Quote from: JD on September 29, 2012, 02:31:37 pmAny thoughts,
suggestions?

JD

I am guessing you get a sigsegv or something along those line try the
following.

Code: [Select]{*******************************************************
************
*  TsSpreadBIFF8Writer.WriteToFile ()
*
*  DESCRIPTION:    Writes an Excel BIFF8 file to the disc
*
*                  The BIFF 8 writer overrides this method because
*                  BIFF 8 is written as an OLE document, and our
*                  current OLE document writing method involves:
*
*                  1 - Writing the BIFF data to a memory stream
*
*                  2 - Write the memory stream data to disk using
*                      COM functions
*
*******************************************************************}
procedure TsSpreadBIFF8Writer.WriteToFile(const AFileName: string;
  AData: TsWorkbook; const AOverwriteExisting: Boolean);
var
  MemStream: TMemoryStream;
  OutputStorage: TOLEStorage;
  OLEDocument: TOLEDocument;
begin
  MemStream := TMemoryStream.Create;
  OutputStorage := TOLEStorage.Create;
  try
    WriteToStream(MemStream, AData);

    // Only one stream is necessary for any number of worksheets
    OLEDocument.Stream := MemStream;

    OutputStorage.WriteOLEFile(AFileName, OLEDocument,
AOverwriteExisting, 'Workbook');
  finally
    OLEDocument.Stream := nil;//make sure that it doesn't try to
access the stream after is freed.
    MemStream.Free;              
    OutputStorage.Free;
  end;
end;

To be sure take a look on the OLEDocument.Stream property what it does
in the SetStream (or something along those lines) setter method used
if it has code along the lines of
Code: [Select]begin
    If LocalStreamVar = AValue then exit;
    LocalStreamVar := AValue;
end;
then the above suggestion should stop the error, If on the other hand
you see code that it copies the stream data in an internal structure
then probably the above will not fix it either.

Regards
Jo.

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JD · 2012-10-01 16:43

It dosen't work. The error remains there. I'll just leave it like that
until I can contact the package maintainer or wait & see if it will be
corrected in SVN.

Thanks for your suggestion.