Problem with substr()

[paul2ashton]

Hi, new member here
I am trying to extract filenames from a file.
When my string is preset the code works ok but
when I read lines in from a file it does not work.
Can anyone see the error of my ways.

Many thanks in advance, Paul.

#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

main()
{
   string filename;
   string str1;
   
   // Why won't it work when reading from a file
   ifstream myfile ("data.txt");
   if (myfile.is_open())
   {
      while (! myfile.eof() )
      {
            getline (myfile,str1);

            //string str1( "p4 = file128.dat, 128" ); // This works ok
            string::size_type pos1 = str1.find( "=", 0 );
            string::size_type pos2 = str1.find( ",", 0 );
   
            cout << str1 << endl;

            // Extract the filename
            filename = str1.substr (pos1 + 2,((pos2 - pos1)-2));// substr fault with files ?
            cout << filename << endl;
      }
      
    myfile.close();
  }
   system("PAUSE");	
}

// This is the data.txt file to be opened
/*
'ignore any lines that start with a comment
'ignore any lines that start with a comment

p1 = file1.dat, 0
p2 = file2.dat, 2
p3 = file22.dat, 22
p4 = file100.dat, 100
*/

Program should output...

file1.dat
file2.dat
file22.dat
file100.dat

[Duthomhas]

It works fine for me.

But you don't account for lines that aren't of the form

"x = y, z"

You must, at the very least, account for blank lines. If you plan to have commentary you'll also want to check for and skip those lines.

Good luck!

[paul2ashton]

Yes, thank you Duoas.

Substr Pos1 and pos2 are reading out of bounds and causing the error when passed a blank line. Problem fixed :)

Regards Paul