QFile map

[weixj2003ld]

Now I need to read/write a large file(15G),I want to accelerate the speed of reading /writing file, I find that the map function of QFilecan do it,I try it as follows,but I find that speed is the same as the common read/write file,why?

QFile objInputFile("test.sgy");   
    if (!objInputFile.open(QIODevice::Unbuffered | QIODevice::ReadOnly))   
    {  
        return false;   
    }   
 
    QFile objOutputFile("out.sgy");   
    if (!objOutputFile.open(QIODevice::Unbuffered | QIODevice::WriteOnly | QIODevice::Truncate))   
    { 
        objInputFile.close();   
        return false;   
    }   
 
    uchar * pData = NULL;   
    qint64 m_qint64FileOffset = 0;
    qint64 m_qint64InputFileSize = objInputFile.size(); 
	qint64 m_unBlockSize=m_qint64InputFileSize;
 
    qint64 unTmpBlockSize = m_qint64InputFileSize/10;   
 
    while(m_qint64FileOffset < m_qint64InputFileSize)   
    {   
       if (m_qint64InputFileSize-m_qint64FileOffset <unTmpBlockSize)  		
              unTmpBlockSize=m_qint64InputFileSize-m_qint64FileOffset;		
        pData = objInputFile.map(m_qint64FileOffset,unTmpBlockSize);
 
        if (pData == NULL)   
        {   
            objInputFile.close();   
            objOutputFile.close();   
            return false;   
        }   
        if (objOutputFile.write((char*)pData,unTmpBlockSize) == -1)   
        {   
            objInputFile.close();   
            objOutputFile.close();   
            return false;   
        }   
 
        m_qint64FileOffset += unTmpBlockSize;   
        if (!objInputFile.unmap(pData))   
        {   
            objInputFile.close();   
            objOutputFile.close();   
            return false;   
        }   
    } 
 
    objInputFile.unmap(pData);   
    objInputFile.close();   
    objOutputFile.close();   
    return true;

QFile objInputFile("test.sgy");   
    if (!objInputFile.open(QIODevice::Unbuffered | QIODevice::ReadOnly))   
    {  
        return false;   
    }   
  
    QFile objOutputFile("out.sgy");   
    if (!objOutputFile.open(QIODevice::Unbuffered | QIODevice::WriteOnly | QIODevice::Truncate))   
    { 
        objInputFile.close();   
        return false;   
    }   
  
    uchar * pData = NULL;   
    qint64 m_qint64FileOffset = 0;
    qint64 m_qint64InputFileSize = objInputFile.size(); 
	qint64 m_unBlockSize=m_qint64InputFileSize;

    qint64 unTmpBlockSize = m_qint64InputFileSize/10;   
		
    while(m_qint64FileOffset < m_qint64InputFileSize)   
    {   
       if (m_qint64InputFileSize-m_qint64FileOffset <unTmpBlockSize)  		
              unTmpBlockSize=m_qint64InputFileSize-m_qint64FileOffset;		
        pData = objInputFile.map(m_qint64FileOffset,unTmpBlockSize);

        if (pData == NULL)   
        {   
            objInputFile.close();   
            objOutputFile.close();   
            return false;   
        }   
        if (objOutputFile.write((char*)pData,unTmpBlockSize) == -1)   
        {   
            objInputFile.close();   
            objOutputFile.close();   
            return false;   
        }   
  
        m_qint64FileOffset += unTmpBlockSize;   
        if (!objInputFile.unmap(pData))   
        {   
            objInputFile.close();   
            objOutputFile.close();   
            return false;   
        }   
    } 

    objInputFile.unmap(pData);   
    objInputFile.close();   
    objOutputFile.close();   
    return true;

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[squidge]

For large files, the speed will be the same regardless of the method you use because the overall performance will be based on the OS/disk controller and disks themselves rather than the overhead of the libraries you are using.