demo_fileflush

//+------------------------------------------------------------------+
//|                                               Demo_FileFlush.mq5 |
//|                        Copyright 2013, MetaQuotes Software Corp. |
//|                                              http://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2013, MetaQuotes Software Corp."
#property link      "http://www.mql5.com"
#property version   "1.00"
//--- show the window of input parameters when launching the script
#property script_show_inputs
//--- file name for writing
input string InpFileName="example.csv"; // file name
//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
//--- reset error value
   ResetLastError();
//--- open the file
   int file_handle=FileOpen(InpFileName,FILE_READ|FILE_WRITE|FILE_CSV);
   if(file_handle!=INVALID_HANDLE)
     {
      //--- write data to the file
      for(int i=0;i<1000;i++)
        {
         //--- call write function
         FileWrite(file_handle,TimeCurrent(),SymbolInfoDouble(Symbol(),SYMBOL_BID),SymbolInfoDouble(Symbol(),SYMBOL_ASK));
         //--- save data on the disk at each 128th iteration
         if((i & 127)==127)
           {
            //--- now, data will be located in the file and will not be lost in case of a critical error
            FileFlush(file_handle);
            PrintFormat("i = %d, OK",i);
           }
         //--- 0.01 second pause
         Sleep(10);
        }
      //--- close the file
      FileClose(file_handle);
     }
   else
      PrintFormat("Error, code = %d",GetLastError());
  }
//+------------------------------------------------------------------+