IRow：：Open 仅支持要打开DBGUID_STREAM和DBGUID_NULL类型的对象。
以下函数使用 IRow：：Open 和 ISequentialStream 提取大数据。
void InitializeAndExecuteCommand()
{
ULONG iidx;
WCHAR* wCmdString=OLESTR("SELECT * FROM MyTable");
// Do the initialization, create the session, and set command text.
hr = pICommandText->Execute(NULL, IID_IRow, NULL,
&cNumRows,(IUnknown **)&pIRow)))
//Get 1 column at a time.
for(ULONG i=1; i <= NoOfColumns; i++)
GetSequentialColumn(pIRow, iidx);
// Do the clean up.
}
HRESULT GetSequentialColumn(IRow* pUnkRow, ULONG iCol)
{
HRESULT hr = NOERROR;
ULONG cbRead = 0;
ULONG cbTotal = 0;
ULONG cColumns = 0;
ULONG cReads = 0;
ISequentialStream* pIStream = NULL;
WCHAR* pBuffer[kMaxBuff]; //50 chars read by ISequentialStream::Read()
DBCOLUMNINFO* prgInfo;
OLECHAR* pColNames;
IColumnsInfo* pIColumnsInfo;
DBID columnid;
DBCOLUMNACCESS column;
hr = pUnkRow->QueryInterface(IID_IColumnsInfo,
(void**) &pIColumnsInfo);
hr = pIColumnsInfo->GetColumnInfo(&cColumns, &prgInfo, &pColNames);
// Get Column ID.
columnid = (prgInfo + (iCol - 1))->columnid;
// Get sequential stream object by calling IRow::Open.
hr = pUnkRow->Open(NULL, &columnid, DBGUID_STREAM, 0,
IID_ISequentialStream,(LPUNKNOWN *)&pIStream);
ZeroMemory(pBuffer, kMaxBuff * sizeof(WCHAR));
// Read 50 chars at a time until no more data.
do
{
hr = pIStream->Read(pBuffer, kMaxBuff, &cbRead);
cbTotal = cbTotal + cbRead;
// Process the data.
} while(cbRead > 0);
// Do the clean up.
return hr;
}
可以使用 ISequentialStream 接口绑定或检索大型数据。 对于绑定列，状态标志指示是否通过设置DBSTATUS_S_TRUNCATED截断数据。