ado 读写二进制数据

1. 写二进制数据：
   pRs->AppendChunk(_T("tpContent"),buff,dwLen);
2. 读二进制数据：

     CADOFieldInfo info;   
      pRs->GetFieldInfo(_T("tpcontent"),&info); //topology设备上下文，在数据表中以二进制存在
      void *buff=malloc(info.m_lSize);
      memset(buff,0,info.m_lSize);
      pRs->GetChunk(_T("tpcontent"),buff);  //使用tpcontent字段的内容来填充buff
     

   pRs是自己封装的一个类，CADORecordset，其他的定义：

   _RecordsetPtr m_pRecordset

   BOOL CADORecordset::AppendChunk(LPCTSTR lpFieldName, LPVOID lpData, UINT nBytes){FieldPtr pField = m_pRecordset->Fields->GetItem(lpFieldName);return AppendChunk(pField, lpData, nBytes);}BOOL CADORecordset::AppendChunk(int nIndex, LPVOID lpData, UINT nBytes){_variant_t vtIndex;vtIndex.vt = VT_I2;vtIndex.iVal = nIndex;FieldPtr pField = m_pRecordset->Fields->GetItem(vtIndex);return AppendChunk(pField, lpData, nBytes);}BOOL CADORecordset::AppendChunk(FieldPtr pField, LPVOID lpData, UINT nBytes){HRESULT hr;_variant_t varChunk;long lngOffset = 0;UCHAR chData;SAFEARRAY FAR *psa = NULL;SAFEARRAYBOUND rgsabound[1];try{//Create a safe array to store the array of BYTES rgsabound[0].lLbound = 0;rgsabound[0].cElements = nBytes;psa = SafeArrayCreate(VT_UI1,1,rgsabound);while(lngOffset < (long)nBytes){chData= ((UCHAR*)lpData)[lngOffset];hr = SafeArrayPutElement(psa, &lngOffset, &chData);if(FAILED(hr))return FALSE;lngOffset++;}lngOffset = 0;//Assign the Safe array  to a variant. varChunk.vt = VT_ARRAY|VT_UI1;varChunk.parray = psa;hr = pField->AppendChunk(varChunk);if(SUCCEEDED(hr)) return TRUE;}catch(_com_error &e){dump_com_error(e);return FALSE;}return FALSE;}

   
    

   BOOL CADORecordset::GetFieldInfo(FieldPtr pField, CADOFieldInfo* fldInfo){memset(fldInfo, 0, sizeof(CADOFieldInfo));strcpy(fldInfo->m_strName, (LPCTSTR)pField->GetName());fldInfo->m_lDefinedSize = pField->GetDefinedSize();fldInfo->m_nType = pField->GetType();fldInfo->m_lAttributes = pField->GetAttributes();if(!IsEof())fldInfo->m_lSize = pField->GetActualSize();return TRUE;}BOOL CADORecordset::GetChunk(LPCTSTR lpFieldName, LPVOID lpData){FieldPtr pField = m_pRecordset->Fields->GetItem(lpFieldName);return GetChunk(pField, lpData);}BOOL CADORecordset::GetChunk(int nIndex, LPVOID lpData){_variant_t vtIndex;vtIndex.vt = VT_I2;vtIndex.iVal = nIndex;FieldPtr pField = m_pRecordset->Fields->GetItem(vtIndex);return GetChunk(pField, lpData);}BOOL CADORecordset::GetChunk(FieldPtr pField, LPVOID lpData){long lngSize, lngOffSet = 0;_variant_t varChunk;    UCHAR chData;HRESULT hr;long lBytesCopied = 0;lngSize = pField->ActualSize;while(lngOffSet < lngSize){ try{varChunk = pField->GetChunk(ChunkSize);//Copy the data only upto the Actual Size of Field.              for(long lIndex = 0; lIndex <= (ChunkSize - 1); lIndex++)            {                hr= SafeArrayGetElement(varChunk.parray, &lIndex, &chData);                if(SUCCEEDED(hr))                {                    //Take BYTE by BYTE and advance Memory Location                    //hr = SafeArrayPutElement((SAFEARRAY FAR*)lpData, &lBytesCopied ,&chData); ((UCHAR*)lpData)[lBytesCopied] = chData;                    lBytesCopied++;                }                else                    break;            }lngOffSet += ChunkSize;}catch(_com_error &e){dump_com_error(e);return FALSE;}}lngOffSet = 0;return TRUE;}