Handling the Structured Storage of SAFEARRAYs

An ATL-derived class to handle the structured storage of SAFEARRAYs (CComVariantEx).

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Environment: VC6 (ATL), NT4/2000/XP

Currently, the ATL CComVariant object can store itself to a "Structured Storage" file via the functions CComVariant::WriteToFile() and CComVariant::ReadFromFile(). However, this does not support CComVariant objects that contain SAFEARRAYs. Below is a derived CComVariantEx class in which these functions have been extended to support CComVariants that contain one-dimensional SAFEARRAYs of VT_VARIANT.

Feel free to extend this class to support multidimensional SAFEARRAYs.

// update to CComVariant to store SAFEARRAYs to the stream
class CComVariantEx : public CComVariant  
{
public:

  HRESULT WriteToStream(IStream* pStream);
  HRESULT ReadFromStream(IStream* pStream);
  
};


inline HRESULT CComVariantEx::WriteToStream(IStream* pStream)
{
  HRESULT hr(E_FAIL);

  // enhancement to stream SAFEARRAYs containing VARIANTs

  if((vt&VT_TYPEMASK)==vt)
  {
    hr = CComVariant::WriteToStream(pStream);
  }
  else if((VT_ARRAY|VT_VARIANT)==vt)
  {
    hr = pStream->Write(&vt, sizeof(VARTYPE), NULL);

    if( SUCCEEDED(hr) )
    {
      CComVariantEx* pvData = NULL;

      hr = SafeArrayAccessData(parray, (void HUGEP**)&pvData);

      if( SUCCEEDED(hr) )
      {
        // only support 1-dimensional arrays
        if( 1==SafeArrayGetDim(parray) )
        {
          hr = E_FAIL;

          SAFEARRAYBOUND bnds;

          long bnd(0);
          HRESULT hr1 = SafeArrayGetLBound(parray,1,&bnd);
          bnds.lLbound = bnd;
          HRESULT hr2 = SafeArrayGetUBound(parray,1,&bnd);
          bnds.cElements = 1 + bnd - bnds.lLbound;

          if( SUCCEEDED(hr1) && SUCCEEDED(hr2) )
          {
            // write the SAFEARRAYBOUND information to the stream
            hr = pStream->Write(&bnds,
                                sizeof(SAFEARRAYBOUND), 
                                NULL);

            // write all the variants in the SAFEARRAY to the stream
            for(DWORD i=0;i&ltbnds.cElements && SUCCEEDED(hr);i++)
            {
              // write element to the stream
              hr = pvData[i].WriteToStream(pStream);
            }
          }
        }

        SafeArrayUnaccessData(parray);
      }
    }
  }
  else if( vt==VT_NULL||vt==VT_EMPTY )
  {
    // write the type and nothing else following it
    hr = pStream->Write(&vt, sizeof(VARTYPE), NULL);
  }

  return hr;
}

inline HRESULT CComVariantEx::ReadFromStream(IStream* pStream)
{
  ATLASSERT(pStream != NULL);
  HRESULT hr(E_FAIL);

  hr = VariantClear(this);

  VARTYPE vtRead(VT_NULL);

  if(SUCCEEDED(hr))
  {
    DWORD dwBytesRead(0);
    hr = pStream->Read(&vtRead, sizeof(VARTYPE), &dwBytesRead);
    if (hr == S_FALSE || dwBytesRead==0)
      hr = E_FAIL;
  }

  if (FAILED(hr))
    return hr;
  
  if((vtRead&VT_TYPEMASK)==vtRead)
  {
    LARGE_INTEGER llMove;
    llMove.QuadPart = -(LONGLONG)sizeof(VARTYPE);

    // need to reset to just before the VARTYPE bytes 
    // before calling ReadToStream
    hr = pStream->Seek(llMove,STREAM_SEEK_CUR,NULL);

    if( SUCCEEDED(hr) )
    {
      hr = CComVariant::ReadFromStream(pStream);
    }
  }
  else if((VT_ARRAY|VT_VARIANT)==vtRead)
  {
    // get the bounds of the one dimensional safearray 
    // from the stream
    SAFEARRAYBOUND bnds;
    hr = pStream->Read(&bnds, sizeof(SAFEARRAYBOUND), NULL);

    if( SUCCEEDED(hr) )
    {
      hr = E_FAIL;

      // create a new SAFEARRAY to hold the streamed data
      vt = VT_ARRAY|VT_VARIANT;
      parray = SafeArrayCreateEx(VT_VARIANT,1,&bnds,NULL);
        
      if( parray )
      {
        CComVariantEx* pvData=NULL;
        hr = SafeArrayAccessData( parray,
                                  (void HUGEP**) &pvData);

        if( SUCCEEDED(hr) )
        {
          // read all the variants in the stream to 
          // the SAFEARRAY
          for(DWORD i=0;i&ltbnds.cElements && SUCCEEDED(hr);i++)
          {
            // Read element from the stream
            hr = pvData[i].ReadFromStream(pStream);
          }

          SafeArrayUnaccessData(parray);
        }
      }
    }
  }
  else if( vtRead==VT_NULL||vtRead==VT_EMPTY )
  {
    // read the type and nothing else following it
    vt = vtRead;
  }

  return hr;
}



Comments

  • Well Done !!

    Posted by Legacy on 03/19/2003 12:00am

    Originally posted by: Matthias Biel

    Thank you for this piece of code. I'm just wondering why these clever Microsoft guys didn't implement it in first place.
    M$ <=> pain in the ass.

    Reply
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