Question Reading a log file which is currently writen by another application

• Monday, 23 February 2009 8:37 AM

   

   
  

  0
  Hello,
  
  I am trying to read a log file which is written by another application.
  
  Other application is running,and writing lines to log file time to time.
  At the same time I supposed to read log file without lose and as soon as modification occurs.
  
  
  Even I check if the error occurs when opening file,
  I can not get the line written when open file error occurs.
  But it can not get some lines of the log file.
  
  Below you can find the function which I am using to accomplish this job.
  
  
  Thanks a lot
  
  p.s. : I can not modify the other application.
  
  

  while(1)

  {

  loopTry++;

  if(CFile::GetStatus(fileName,filestatus))

  {

  if(filestatus.m_size > lastSize)

  {

  if ( !myFile.Open( fileName, CFile::shareDenyWrite | //

  CFile::modeRead  , &fileException ) )

  {

  CString cs; cs.Format(_T("Can't open file %s, error = %u readTry = %d"),

  fileName, fileException.m_cause,readTry );

  log(cs);

  }

  else//oku

  {

  readTry++;

  char * rBuffer = ::new char[filestatus.m_size+1-cursorPos];

  rBuffer[filestatus.m_size-cursorPos] = '\0';

  //READ START

  myFile.LockRange(0,filestatus.m_size);//

  myFile.Seek(cursorPos, CFile::begin);//TODO: compare seek overhead with reading up to cursorPos

  myFile.Read(rBuffer,filestatus.m_size-cursorPos);

  myFile.UnlockRange(0,filestatus.m_size);

  myFile.Close();

  //READ END

  lastSize = filestatus.m_size;

  //PROCESS START

  std::string str(rBuffer);

  int lineEndPos = 0;

  int localCursor = 0;

  for(;;)

  {

  std::string line;

  int lastNewlineIndex = str.find("\r\n",lineEndPos+1);

  if(lastNewlineIndex == std::string::npos)//if there is no newline left

  {

  break;

  }

  lineEndPos = lastNewlineIndex;

  line = str.substr(localCursor,lineEndPos-localCursor);

  ProcessLine(line,loopTry,readTry);// some func to process line read

  localCursor = lineEndPos + 2;

  cursorPos += localCursor;

  }

  //PROCESS END

  ::delete [] rBuffer;

  }

  }

  else//file size is not changed. wait                {

  Sleep(wait);

  }

  }

  else

  {

  CString cs; cs.Format(_T("can not get status. looptry = %d"),loopTry );

  log(cs);

  }

  }