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Serialize: Appending to a file

Posted on 2000-03-14
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Last Modified: 2013-11-20
I need to save the contents of my document on a file which already has data, this means I must append the data to a file.
How ever, on the document::Serialize function, I use something like this:

void CMyDoc::Serialize(CArchive& ar)
{
// Assume is storing here
    CFile *pFile= ar.GetFile();
    pFile->SeekToEnd();
    ...
    pEditView->SerializeRaw(ar);
}

But it doesn't work, the file is always overwritten... What's wrong???
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Question by:trillo
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RONSLOW earned 50 total points
ID: 2617782
The file is already deleted and recreated by the time you get to the serialize.
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by:RONSLOW
ID: 2617789
Also, appending to a file saved with serialize (via CArchive) will not work (that easily), as you will end up writing the file header twice.
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Expert Comment

by:RONSLOW
ID: 2617792
What you could do is create a temporary CMyDoc object, serialize in from the file you wish to append to, apppend the info from the real CMyDoc object and then serialize out the combined file.
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Author Comment

by:trillo
ID: 2618036
Oh!... And can avoid using the Serialize function.... What if I used CFile directly... will it be the same?
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Expert Comment

by:RONSLOW
ID: 2618311
Actually, if you override the CMyDoc::GetFile so that, if opening for read, it also opens for append, then you should be ok.

eg.

CFile* CMyDoc::GetFile(LPCTSTR lpszFileName, UINT nOpenFlags, CFileException* pError) {
  bool bWriting = CFile::modeCreate == (nOpenFlags & CFile::modeCreate)
  if (bWriting) {
    nOpenFlags |= CFile::modeNoTruncate;
  }
  CFile* pFile = CDocument::GetFile(lpszFileName,nOpenFlags,pError);
  if (bWriting && pFile) {
    pFile->SeekToEnd();
  }
  return pFile;
}

This should ensure that you are appending to the existing file all the time.
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Expert Comment

by:RONSLOW
ID: 2618314
oops that should have read

....if opening for WRITE, it also opens for append, then...
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by:trillo
ID: 2620899
Thanks... Very Helpful
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