Handling the Structured Storage of SAFEARRAYs

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

.

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;
}