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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

HRESULT CSequentialStream::PreAllocBuffer( ULONG uSize )
{
    if( m_uBufferSize < uSize )
    {
        m_uBufferSize = uSize;
        m_pBuffer = CoTaskMemRealloc( m_pBuffer, m_uBufferSize );
        if( m_pBuffer == NULL )
        {
            Clear( );
            return STG_E_INSUFFICIENTMEMORY;
        }
    }
    return S_OK;
}

HRESULT CSequentialStream::Read( void* pv, ULONG cb, ULONG* pcbRead )
{
    ( pcbRead != NULL ? ( * pcbRead = 0U ) : 0 );
    if( pv == NULL ) { return STG_E_INVALIDPOINTER; }
    if( cb == 0U ) { return S_OK; }

    ASSERT( m_uPosition <= m_uBufferUsed );
    ULONG uBytesLeft = m_uBufferUsed - m_uPosition;

    if( uBytesLeft == 0U ) { return S_FALSE; } //no more bytes

    ULONG uBytesRead = ( cb > uBytesLeft ? uBytesLeft : cb );