void QuantumFile::Open(String p_FileName, ArrayIndex p_BufferCount)
{
    QuantumFileHeaderStruct QFHS;
    char *TempBlock;
    QuantumNumber *TempMainObjectBlock;
    QFreeSpaceEntry *TempFreeSpaceBlock;
    ArrayIndex i;
    int FileCreation;
    QFreeSpaceEntry TempFreeSpaceEntry;
    int ProgramVersion;
    int FileVersion;

    m_ReadCount = 0;
    m_WriteCount = 0;
    m_Block.SetSize(p_BufferCount);
    m_BlockNumber.SetSize(p_BufferCount);
    m_BufferModified.SetSize(p_BufferCount);
    m_TimeStamp.SetSize(p_BufferCount);

    if (p_FileName == "")
        {
        m_DosFilePtr = 0;
        return;
        }

    m_DosFilePtr = fopen(p_FileName,"r+b");

    if (m_DosFilePtr == NULL) /* file does not exist */
        {
        FileCreation = TRUE;
        m_DosFilePtr = fopen(p_FileName,"w+b"); /* create it */

        TempBlock = new char[BlockSize];
        TempMainObjectBlock = (QuantumNumber *)TempBlock;
        TempFreeSpaceBlock = (QFreeSpaceEntry *)TempBlock;

        memset((void *)&QFHS,0,sizeof(QuantumFileHeaderStruct));
        QFHS.main_object_index_count = MainObjectIndexCount;
        QFHS.free_space_list_count = MaxFileQuantumCount;
        strcpy(QFHS.quantum_version_info,program_version_info);

        QFHS.main_object_index_offset = BlockSize;
        QFHS.free_space_list_offset = QFHS.main_object_index_offset+
            BlockSize*((MainObjectIndexCount-1)/MainObjectEntriesPerBlock+1);
        QFHS.starting_quantum_offset = QFHS.free_space_list_offset+
            BlockSize*((MaxFileQuantumCount-1)/FreeSpaceEntriesPerBlock+1);

        fseek(m_DosFilePtr,0,SEEK_SET);
        memset(TempBlock,0,BlockSize);
        fwrite(TempBlock,1,BlockSize,m_DosFilePtr); // clear block 0

        fseek(m_DosFilePtr,0,SEEK_SET);
        fwrite(&QFHS,1,sizeof(QuantumFileHeaderStruct), m_DosFilePtr);

        /* clear the main object index */
        memset(TempMainObjectBlock,0,BlockSize);
        TempMainObjectBlock[0] = NoQuantum;
        fseek(m_DosFilePtr,QFHS.main_object_index_offset,SEEK_SET);
        fwrite(TempMainObjectBlock,BlockSize,1,m_DosFilePtr);

        /* clear the free space list */
        TempFreeSpaceEntry.m_FreeSpaceCode = AvailableQuantum;
        TempFreeSpaceEntry.m_ObjectNumber = 0;
        for (i = 0; i < FreeSpaceEntriesPerBlock; i ++)
            TempFreeSpaceBlock[i] = TempFreeSpaceEntry;
        TempFreeSpaceBlock[0].m_FreeSpaceCode = 0; /* Q #0 doesn't exist */
        ArrayIndex FreeSpaceCount = (QFHS.free_space_list_count-1)/
            FreeSpaceEntriesPerBlock+1;
        for (i = 0; i < FreeSpaceCount; i ++)
            {
            fseek(m_DosFilePtr,QFHS.free_space_list_offset+i*BlockSize,SEEK_SET);
            fwrite(TempFreeSpaceBlock,sizeof(QFreeSpaceEntry),
            FreeSpaceEntriesPerBlock,m_DosFilePtr);
            TempFreeSpaceBlock[0].m_FreeSpaceCode = AvailableQuantum;
            }
        delete [] TempBlock;
        }
    else
        {
        FileCreation = FALSE;
        fread(&QFHS,1,sizeof(QuantumFileHeaderStruct),m_DosFilePtr);
        ProgramVersion = atoi(program_version_info);
        FileVersion = atoi(QFHS.quantum_version_info);
        if (ProgramVersion != FileVersion)
            {
            printf("Program version %d does not match file version %d.\n",
            ProgramVersion,FileVersion);
//            exit(1);    // file is newer than program, so forget it
            }
        }

    m_MainObjectStartingBlock = QFHS.main_object_index_offset / BlockSize;
    m_FreeSpaceListStartingBlock = QFHS.free_space_list_offset / BlockSize;
    m_QuantumStartingBlock = QFHS.starting_quantum_offset / BlockSize;
    m_MainObjectCount = QFHS.main_object_index_count;
    m_FreeSpaceListCount = QFHS.free_space_list_count;
    
    for (i = 0; i < p_BufferCount; i ++)
        {
        m_Block[i] = new Block;
        m_BlockNumber[i] = BadBlockNumber;
        m_BufferModified[i] = FALSE;
        m_TimeStamp[i] = 0;
        }

    m_FreeSpaceArray = new FreeSpaceArrayPtr(this);
    m_MainObjectArray = new MainObjectArrayPtr(this);

    if (FileCreation == TRUE) // set up main object name object
        (*m_MainObjectArray)->CreateMainObject("Directory", MainObjectDirectory, 
            MainObjectIndexCount,MainObjectIndexCount);
}