C++切割文件

void CFileCutter::DoSplit()
{
    int nCompleted = 0;   //计数
    CString strSourceFile = m_strSource;  //取得全局变量赋值给局部变量，方便操作
    CString strDestDir = m_strDest;
    CFile sourceFile, destFile;
    //打开文件
    BOOL bOK = sourceFile.Open(strSourceFile, CFile::modeRead | CFile::shareDenyWrite | CFile::typeBinary);
    if (!bOK)//打不开就报错退出
    {
        ::PostMessage(m_hWndNotify, WM_CUTTERSTOP, exitSourceErr, nCompleted);
        return;
    }
    int nPos = 0;
    //逐层创建文件夹（不存在就创建）
    while ((nPos = strDestDir.Find('\', nPos + 1)) != -1)//少了个括号
    {
        ::CreateDirectory(strDestDir.Left(nPos),NULL);
    }
    ::CreateDirectory(strDestDir, NULL);  //创建最底层文件夹
    if (strDestDir.Right(1) != '\')   
    {
        strDestDir += '\';
    }
    int nTotalFiles = sourceFile.GetLength() / m_uFileSize + 1;//判断切割后文件数
    ::PostMessage(m_hWndNotify,WM_CUTTERSTART,nTotalFiles,TRUE); //设置进度条长度
    const int c_page = 4 * 1024;  //每次读取大小
    char buff[c_page]; //缓冲区
    DWORD dwRead;

    CString sDestName;
    int nPreCount = 1;
    UINT uWriteBytes;

    do 
    {
        //设置文件名并创建文件
        sDestName.Format(TEXT("%d_"), nPreCount);
        sDestName += sourceFile.GetFileName();
        if (!destFile.Open(strDestDir + sDestName, CFile::modeWrite | CFile::modeCreate))
        {
            PostMessage(m_hWndNotify, WM_CUTTERSTOP, exitDestErr, nCompleted);
            sourceFile.Close();
            return;
        }
        uWriteBytes = 0;
        do
        {
            //读写操作
            if (!m_bContinue)  //stopCutter函数
            {
                destFile.Close();
                sourceFile.Close();
                if (!m_bExitThread)  //析构函数
                {
                    ::PostMessage(m_hWndNotify, WM_CUTTERSTOP, exitUserForce, nCompleted);
                }
                return;
            }
            dwRead = sourceFile.Read(buff, c_page);//读
            destFile.Write(buff, dwRead); //写
            uWriteBytes += dwRead;  //计数

        } while (dwRead > 0 && uWriteBytes < m_uFileSize);//读出了数据并且一共写的数据量小于用户要求的数据量
        destFile.Close();    //当前文件写完了，关闭
        nCompleted = nPreCount++;  //计数
        ::PostMessage(m_hWndNotify, WM_CUTTERSTATUS, 0, nCompleted);

    } while (dwRead > 0); //只要读出了数据就循环继续，直到源文件全部读出。
    sourceFile.Close(); //最后关闭原文件
    ::PostMessage(m_hWndNotify, WM_CUTTERSTOP, exitSuccess, nCompleted);
}