//+------------------------------------------------------------------+
//| Demo_FileSeek.mq5 |
//| Copyright 2013, MetaQuotes Software Corp. |
//| https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2013, MetaQuotes Software Corp."
#property link "https://www.mql5.com"
#property version "1.00"
//--- display the window of input parameters when launching the script
#property script_show_inputs
//--- input parameters
input string InpFileName="file.txt"; // file name
input string InpDirectoryName="Data"; // directory name
input int InpEncodingType=FILE_ANSI; // ANSI=32 or UNICODE=64
//+------------------------------------------------------------------+
//| Script program start function |
//+------------------------------------------------------------------+
void OnStart()
{
//--- specify the value of the variable for generating random numbers
_RandomSeed=GetTickCount();
//--- variables for positions of the strings' start points
ulong pos[];
int size;
//--- reset the error value
ResetLastError();
//--- open the file
int file_handle=FileOpen(InpDirectoryName+"//"+InpFileName,FILE_READ|FILE_TXT|InpEncodingType);
if(file_handle!=INVALID_HANDLE)
{
PrintFormat("%s file is available for reading",InpFileName);
//--- receive start position for each string in the file
GetStringPositions(file_handle,pos);
//--- define the number of strings in the file
size=ArraySize(pos);
if(!size)
{
//--- stop if the file does not have strings
PrintFormat("%s file is empty!",InpFileName);
FileClose(file_handle);
return;
}
//--- make a random selection of a string number
int ind=MathRand()%size;
//--- shift position to the starting point of the string
if(FileSeek(file_handle,pos[ind],SEEK_SET)==true)
{
//--- read and print the string with ind number
PrintFormat("String text with %d number: \"%s\"",ind,FileReadString(file_handle));
}
//--- close the file
FileClose(file_handle);
PrintFormat("%s file is closed",InpFileName);
}
else
PrintFormat("Failed to open %s file, Error code = %d",InpFileName,GetLastError());
}
//+-------------------------------------------------------------------------------+
//| The function defines starting points for each of the strings in the file and |
//| places them in arr array |
//+-------------------------------------------------------------------------------+
void GetStringPositions(const int handle,ulong &arr[])
{
//--- default array size
int def_size=127;
//--- allocate memory for the array
ArrayResize(arr,def_size);
//--- string counter
int i=0;
//--- if this is not the file's end, then there is at least one string
if(!FileIsEnding(handle))
{
arr[i]=FileTell(handle);
i++;
}
else
return; // the file is empty, exit
//--- define the shift in bytes depending on encoding
int shift;
if(FileGetInteger(handle,FILE_IS_ANSI))
shift=1;
else
shift=2;
//--- go through the strings in the loop
while(1)
{
//--- read the string
FileReadString(handle);
//--- check for the file end
if(!FileIsEnding(handle))
{
//--- store the next string's position
arr[i]=FileTell(handle)+shift;
i++;
//--- increase the size of the array if it is overflown
if(i==def_size)
{
def_size+=def_size+1;
ArrayResize(arr,def_size);
}
}
else
break; // end of the file, exit
}
//--- define the actual size of the array
ArrayResize(arr,i);
}
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