Visual C++中使用OLE DB讀寫SQL Server簡明指南
發布: 2008-4-24 10:49 | 作者: 不詳 | 來源: rdxx | 查看: 82次 | 進入軟件測試論壇討論
pIRowset->ReleaseRows( uRowsObtained, phRows, NULL, NULL, NULL );
pIAccessor->ReleaseAccessor( hAccessor, NULL );
pIAccessor.Release( );
pIRowset.Release( );
讀操作也完成了，是不是仍然很簡單呢？下面我們再來看看最麻煩的二進制數據（text、ntext、image等）的讀寫。要實現BLOB數據的讀寫，我們需要一個輔助的類，定義如下：
class CSequentialStream : public ISequentialStream // BLOB 數據訪問類
{
public:
CSequentialStream( );
virtual ~CSequentialStream( );
virtual BOOL Seek( ULONG uPosition );
virtual BOOL Clear( );
virtual ULONG GetLength( ) { return m_uBufferUsed; };
virtual operator void* const( ) { return m_pBuffer; };
STDMETHODIMP_( ULONG ) AddRef( ) { return ++ m_uRefCount; };
STDMETHODIMP_( ULONG ) Release( ) { ASSERT( m_uRefCount != 0U ); -- m_uRefCount; if( m_uRefCount == 0U ) { delete this; } return m_uRefCount; };
STDMETHODIMP QueryInterface( REFIID riid, LPVOID* ppv );
STDMETHODIMP Read( void __RPC_FAR* pv, ULONG cb, ULONG __RPC_FAR* pcbRead );
STDMETHODIMP Write( const void __RPC_FAR* pv, ULONG cb, ULONG __RPC_FAR* pcbWritten );
void ResetPosition( ) { m_uPosition = 0U; };
HRESULT PreAllocBuffer( ULONG uSize );
private:
ULONG m_uRefCount; // reference count
void* m_pBuffer; // buffer
ULONG m_uBufferUsed; // buffer used