C / C++ / MFC

// If the file is an OLE Storage DocFile...
    if (StgIsStorageFile(m_bstrFileName) == S_OK)
    {
     // Get the data from IStorage...
	    hr = StgOpenStorage(m_bstrFileName, NULL, dwOpenMode, NULL, 0, &m_pStorage);

     // If we failed to gain write access, try to just read access if caller allows
	 // it. This function will open the OLE file in transacted read mode, which
	 // covers cases where the file is in use or is on a read-only share. We can't
	 // save after the open so we force the read-only flag on...
        if (((hr == STG_E_ACCESSDENIED) || (hr == STG_E_SHAREVIOLATION)) && 
            (m_dwFlags & dsoOptionOpenReadOnlyIfNoWriteAccess))
        {
            m_fReadOnly = TRUE;
	        hr = StgOpenStorage(m_bstrFileName, NULL, 
				(STGM_READ | STGM_TRANSACTED | STGM_SHARE_DENY_NONE), NULL, 0, &m_pStorage);
        }
        
	 // If we are lucky, we have a storage to read from, so ask OLE to open the 
	 // associated property set for the file and return the IPSS iface...
	    if (SUCCEEDED(hr))
        {
            hr = m_pStorage->QueryInterface(IID_IPropertySetStorage, (void**)&m_pPropSetStg);
        }
    }
    else if ((m_dwFlags & dsoOptionOnlyOpenOLEFiles) != dsoOptionOnlyOpenOLEFiles)
    {
	 // If caller would like non-OLE property sets, we can try to provide them. There
	 // are two types: (1) explicit metadata handlers registered by file type; or (2) 
	 // NTFS 5.0+ property stream data in NTFS file header (which is actually saved as
	 // alternate stream). The former is custom provider to save data inside the file 
	 // without using OLE. The later is available for any file on NTFS5 disk.
		CLSID clsidMetaHandler = {0};
		IPersistFile *prtsf = NULL;

		if (DsoGetMetaHandler(m_bstrFileName, &clsidMetaHandler) == S_OK)
		{
		 // Create instance of the Metadata Handler object...
			hr = CoCreateInstance(clsidMetaHandler, NULL, CLSCTX_INPROC, IID_IPersistFile, (void**)&prtsf);
			if (SUCCEEDED(hr))
			{
			 // Ask it to load the file for parsing...
				hr = prtsf->Load(m_bstrFileName, dwOpenMode);
				if (SUCCEEDED(hr))
				{
				 // If it succeeded, ask for the property set storage...
					hr = prtsf->QueryInterface(IID_IPropertySetStorage, (void**)&m_pPropSetStg);
					if (SUCCEEDED(hr)){ASSIGN_INTERFACE(m_pPrstFile, prtsf);}
				}
				prtsf->Release();	
			}
			else hr = DSO_E_NODOCUMENTPROPS; // bad news, unable to load handler.
		}
		else if (v_pfnStgOpenStorageEx)
		{
		 // On Win2K+ we can try and open plain files on NTFS 5.0 drive and get 
		 // the NTFS version of OLE properties (saved in alt stream)...
			hr = (v_pfnStgOpenStorageEx)(m_bstrFileName, dwOpenMode, STGFMT_FILE, 0, NULL, 0, 
					IID_IPropertySetStorage, (void**)&m_pPropSetStg);

		 // If we failed to gain write access, try to just read access if caller
		 // wants us to. This only works for access block, not share violations...
		   if ((hr == STG_E_ACCESSDENIED) && (!m_fReadOnly) && 
				(m_dwFlags & dsoOptionOpenReadOnlyIfNoWriteAccess))
			{
				m_fReadOnly = TRUE;
				hr = (v_pfnStgOpenStorageEx)(m_bstrFileName, (STGM_READ | STGM_SHARE_EXCLUSIVE), STGFMT_FILE,
					0, NULL, 0, IID_IPropertySetStorage, (void**)&m_pPropSetStg);
			}
		}