Hi all, My first time use dynamic_bitset like the following way: int index = m_pData->Size(); U8* pData = m_pData->DataBuffer(); boost::dynamic_bitset<>temp(8,pData[index - 1]); int i = 0; for (i = index - 2; i >= 0; i--) { temp.append(pData[i]); temp.resize((index -i)*8); } m_RowBitTag = temp; Here the U8 is unsigned char. When run to temp.append(pData[i]); it will get an unhandled exception. My environment is VC++ 6 Best Regards, -Ronnie