Re: Skipping parts of a serialized file

From:

Scoots <linkingfire@msn.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 23 Mar 2009 06:50:36 -0700 (PDT)

Message-ID:

<30fe1e7e-0770-4edb-af6c-94ff3c4f9bed@s22g2000prg.googlegroups.com>

Following the suggestions of others, I added the lpstorage and
COleStreamFile code from the COleDocument loading algorithm, and this
appears to do the trick. I have not stress-tested this yet, but the
following appears to work:

bool Decoder::OpenAndReadPreamble(CString p_csFilename,
COleStreamFile* p_pfr)
{
    //The preamble is completely and utterly unimportant. This gets
written
    //even if (Name removed for confidentiality) doesn't even save the
file! It's runtime information left over
    //from serialization. We just... plain... don't care.

    LPSTORAGE lpRootStg = NULL;

    //This is based on the COleDocument code for reading.
    BOOL bResult = FALSE;
    TRY
    {
        if (lpRootStg == NULL)
        {
            LPCOLESTR lpsz = T2COLE(p_csFilename);

            // use STGM_CONVERT if necessary
            SCODE sc;
            LPSTORAGE lpStorage = NULL;
            if (StgIsStorageFile(lpsz) == S_FALSE)
            {
                // convert existing storage file
                sc = StgCreateDocfile(lpsz, STGM_READWRITE|
                    STGM_TRANSACTED|/*STGM_SHARE_EXCLUSIVE|*/STGM_CONVERT,
                    0, &lpStorage);
                if (FAILED(sc) || lpStorage == NULL)
                    sc = StgCreateDocfile(lpsz, STGM_READ|
                            STGM_TRANSACTED|/*STGM_SHARE_EXCLUSIVE|*/STGM_CONVERT,
                            0, &lpStorage);
            }
            else
            {
                // open new storage file
                sc = StgOpenStorage(lpsz, NULL,
                    STGM_READWRITE|STGM_TRANSACTED/*|STGM_SHARE_EXCLUSIVE*/,
                    0, 0, &lpStorage);
                if (FAILED(sc) || lpStorage == NULL)
                    sc = StgOpenStorage(lpsz, NULL,
                        STGM_READ|STGM_TRANSACTED/*|STGM_SHARE_EXCLUSIVE*/,
                        0, 0, &lpStorage);
            }
            if (FAILED(sc))
                AfxThrowOleException(sc);

            ASSERT(lpStorage != NULL);
            lpRootStg = lpStorage;
        }

    ASSERT(lpRootStg != NULL);

    // open Contents stream
    CFileException fe;
    if (!p_pfr->OpenStream(lpRootStg, _T("Contents"),
            CFile::modeRead|CFile::shareExclusive, &fe) &&
        !p_pfr->CreateStream(lpRootStg, _T("Contents"),
            CFile::modeRead|CFile::shareExclusive|CFile::modeCreate, &fe))
    {
        if (fe.m_cause == CFileException::fileNotFound)
            AfxThrowArchiveException(CArchiveException::badSchema);
        else
            AfxThrowFileException(fe.m_cause, fe.m_lOsError);
    }

    // load it with CArchive (loads from Contents stream)
    CArchive loadArchive(p_pfr, CArchive::load |
CArchive::bNoFlushOnDelete);
          }
          CATCH_ALL(e)
          {
    MessageBox(NULL,_T("Whoops"), _T("We did something bad."), MB_OK);
                return false;

          }
         END_CATCH_ALL

  return true;
}

Okay, so there is a fair amount of debugging left to do, and nevermind
the fact that the messagebox is completely uninformative or that I
haven't commented it, this appears to automatically handle the
variable size header information. I'll let you know as I test it
more.
~Scoots