mitab_rawbinblock.cpp

用于读取TAB、MIF、SHP文件的类

    return 0;
}


/**********************************************************************
 *                   TABRawBinBlock::GetBlockType()
 *
 * Return the block type for the current object.
 *
 * Returns a block type >= 0 if succesful or -1 if an error happened, in 
 * which case  CPLError() will have been called.
 **********************************************************************/
int     TABRawBinBlock::GetBlockType()
{
    if (m_pabyBuf == NULL)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "GetBlockType(): Block has not been initialized.");
        return -1;
    }

    if (m_nBlockType > TABMAP_LAST_VALID_BLOCK_TYPE)
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "GetBlockType(): Unsupported block type %d.", 
                 m_nBlockType);
        return -1;
    }

    return m_nBlockType;
}

/**********************************************************************
 *                   TABRawBinBlock::GotoByteInBlock()
 *
 * Move the block pointer to the specified position relative to the 
 * beginning of the block.
 *
 * Returns 0 if succesful or -1 if an error happened, in which case 
 * CPLError() will have been called.
 **********************************************************************/
int     TABRawBinBlock::GotoByteInBlock(int nOffset)
{
    if ( (m_eAccess == TABRead && nOffset > m_nSizeUsed) ||
         (m_eAccess != TABRead && nOffset > m_nBlockSize) )
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "GotoByteInBlock(): Attempt to go past end of data block.");
        return -1;
    }

    if (nOffset < 0)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
               "GotoByteInBlock(): Attempt to go before start of data block.");
        return -1;
    }

    m_nCurPos = nOffset;
    
    m_nSizeUsed = MAX(m_nSizeUsed, m_nCurPos);

    return 0;
}

/**********************************************************************
 *                   TABRawBinBlock::GotoByteRel()
 *
 * Move the block pointer by the specified number of bytes relative
 * to its current position.
 *
 * Returns 0 if succesful or -1 if an error happened, in which case 
 * CPLError() will have been called.
 **********************************************************************/
int     TABRawBinBlock::GotoByteRel(int nOffset)
{
    return GotoByteInBlock(m_nCurPos + nOffset);
}

/**********************************************************************
 *                   TABRawBinBlock::GotoByteInFile()
 *
 * Move the block pointer to the specified position relative to the 
 * beginning of the file.  
 * 
 * In read access, the current block may be reloaded to contain a right
 * block of binary data if necessary.
 *
 * In write mode, the current block may automagically be committed to 
 * disk and a new block initialized if necessary.
 *
 * bForceReadFromFile is used in write mode to read the new block data from
 * file instead of creating an empty block. (Useful for TABCollection
 * or other cases that need to do random access in the file in write mode.)
 *
 * Returns 0 if succesful or -1 if an error happened, in which case 
 * CPLError() will have been called.
 **********************************************************************/
int     TABRawBinBlock::GotoByteInFile(int nOffset, 
                                       GBool bForceReadFromFile /*=FALSE*/)
{
    int nNewBlockPtr;

    if (nOffset < 0)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
               "GotoByteInFile(): Attempt to go before start of file.");
        return -1;
    }

    nNewBlockPtr = ( (nOffset-m_nFirstBlockPtr)/m_nBlockSize)*m_nBlockSize +
                     m_nFirstBlockPtr;

    if (m_eAccess == TABRead)
    {
        if ( (nOffset<m_nFileOffset || nOffset>=m_nFileOffset+m_nSizeUsed) &&
             ReadFromFile(m_fp, nNewBlockPtr, m_nBlockSize) != 0)
        {
            // Failed reading new block... error has already been reported.
            return -1;
        }
    }
    else if (m_eAccess == TABWrite)
    {
        if ( (nOffset<m_nFileOffset || nOffset>=m_nFileOffset+m_nBlockSize) &&
             (CommitToFile() != 0 ||
              InitNewBlock(m_fp, m_nBlockSize, nNewBlockPtr) != 0 ) )
        {
            // Failed reading new block... error has already been reported.
            return -1;
        }
    }
    else if (m_eAccess == TABReadWrite)
    {
        // TODO: THIS IS NOT REAL read/write access (it's more extended write)
        // Currently we try to read from file only if explicitly requested.
        // If we ever want true read/write mode we should implement
        // more smarts to detect whether the caller wants an existing block to
        // be read, or a new one to be created from scratch.
        // CommitToFile() should only be called only if something changed.
        //
        if ( (nOffset<m_nFileOffset || nOffset>=m_nFileOffset+m_nBlockSize) &&
             (CommitToFile() != 0 ||
              (!bForceReadFromFile && 
               InitNewBlock(m_fp, m_nBlockSize, nNewBlockPtr) != 0) ||
              (bForceReadFromFile &&
               ReadFromFile(m_fp, nNewBlockPtr, m_nBlockSize) != 0) )  )
        {
            // Failed reading new block... error has already been reported.
            return -1;
        }
    }
    else
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Access mode not supported yet!");
        return -1;
    }

    m_nCurPos = nOffset-m_nFileOffset;

    m_nSizeUsed = MAX(m_nSizeUsed, m_nCurPos);

    return 0;
}


/**********************************************************************
 *                   TABRawBinBlock::SetFirstBlockPtr()
 *
 * Set the position in the file at which the first block starts.
 * This value will usually be the header size and needs to be specified 
 * only if the header size is different from the other blocks size. 
 *
 * This value will be used by GotoByteInFile() to properly align the data
 * blocks that it loads automatically when a requested position is outside
 * of the block currently in memory.
 **********************************************************************/
void  TABRawBinBlock::SetFirstBlockPtr(int nOffset)
{
    m_nFirstBlockPtr = nOffset;
}


/**********************************************************************
 *                   TABRawBinBlock::GetNumUnusedBytes()
 *
 * Return the number of unused bytes in this block.
 **********************************************************************/
int     TABRawBinBlock::GetNumUnusedBytes()
{
    return (m_nBlockSize - m_nSizeUsed);
}

/**********************************************************************
 *                   TABRawBinBlock::GetFirstUnusedByteOffset()
 *
 * Return the position of the first unused byte in this block relative
 * to the beginning of the file, or -1 if the block is full.
 **********************************************************************/
int     TABRawBinBlock::GetFirstUnusedByteOffset()
{
    if (m_nSizeUsed < m_nBlockSize)
        return m_nFileOffset + m_nSizeUsed;
    else
        return -1;
}

/**********************************************************************
 *                   TABRawBinBlock::GetCurAddress()
 *
 * Return the current pointer position, relative to beginning of file.
 **********************************************************************/
int     TABRawBinBlock::GetCurAddress()
{
    return (m_nFileOffset + m_nCurPos);
}

/**********************************************************************
 *                   TABRawBinBlock::ReadBytes()
 *
 * Copy the number of bytes from the data block's internal buffer to
 * the user's buffer pointed by pabyDstBuf.
 *
 * Passing pabyDstBuf = NULL will only move the read pointer by the
 * specified number of bytes as if the copy had happened... but it 
 * won't crash.
 *
 * Returns 0 if succesful or -1 if an error happened, in which case 
 * CPLError() will have been called.
 **********************************************************************/
int     TABRawBinBlock::ReadBytes(int numBytes, GByte *pabyDstBuf)
{
    /*----------------------------------------------------------------
     * Make sure block is initialized with Read access and that the
     * operation won't go beyond the buffer's size.
     *---------------------------------------------------------------*/
    if (m_pabyBuf == NULL)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "ReadBytes(): Block has not been initialized.");
        return -1;
    }

    if (m_eAccess != TABRead && m_eAccess != TABReadWrite )
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "ReadBytes(): Block does not support read operations.");
        return -1;
    }

    if (m_nCurPos + numBytes > m_nSizeUsed)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "ReadBytes(): Attempt to read past end of data block.");
        return -1;
    }

    if (pabyDstBuf)
    {
        memcpy(pabyDstBuf, m_pabyBuf + m_nCurPos, numBytes);
    }

    m_nCurPos += numBytes;

    return 0;
}

/**********************************************************************
 *                   TABRawBinBlock::Read<datatype>()
 *
 * MapInfo files are binary files with LSB first (Intel) byte 
 * ordering.  The following functions will read from the input file
 * and return a value with the bytes ordered properly for the current 
 * platform.
 **********************************************************************/
GByte  TABRawBinBlock::ReadByte()
{
    GByte byValue;

    ReadBytes(1, (GByte*)(&byValue));

    return byValue;
}

GInt16  TABRawBinBlock::ReadInt16()
{
    GInt16 n16Value;

    ReadBytes(2, (GByte*)(&n16Value));

#ifdef CPL_MSB
    return (GInt16)CPL_SWAP16(n16Value);
#else
    return n16Value;
#endif
}

GInt32  TABRawBinBlock::ReadInt32()
{
    GInt32 n32Value;

    ReadBytes(4, (GByte*)(&n32Value));

#ifdef CPL_MSB
    return (GInt32)CPL_SWAP32(n32Value);
#else
    return n32Value;
#endif
}

float   TABRawBinBlock::ReadFloat()
{
    float fValue;

    ReadBytes(4, (GByte*)(&fValue));

#ifdef CPL_MSB
    *(GUInt32*)(&fValue) = CPL_SWAP32(*(GUInt32*)(&fValue));
#endif
    return fValue;
}

double  TABRawBinBlock::ReadDouble()
{
    double dValue;

    ReadBytes(8, (GByte*)(&dValue));

#ifdef CPL_MSB
    CPL_SWAPDOUBLE(&dValue);
#endif

    return dValue;
}



/**********************************************************************
 *                   TABRawBinBlock::WriteBytes()