how does getline() know what line it's getting???

[LMHmedchem]

May be a silly question, but I often use a combination of getline() and fstream in a while loop to read a delimited text file.

   ifstream read_file;
   stringstream file_data_stream;
   string new_line, new_cell;

   // open the data file into file stream
   read_file.open( input_file.c_str() );

  // read in each line of the index file
   while(getline(read_file, new_line)) {

      // add current row to stringstream
      file_data_stream << new_line;

      // parse stringstream on tab to get fields
      while(getline(file_data_stream, new_cell,'\t')) {
         // the data is now parsed
      }
   }

This will read through the input_file and parse it into "cells" by line and tab. There doesn't seem to be an iterator to allow getline() to keep track of where it is in the file.

I need to read in two files so that I am reading the same line of each file one at a time. In other words, read in the first line of file 1 and then the first line of file 2. I can't see how to do this with the structure above.

If I did something like,

   ifstream read_file1, read_file2;
   stringstream file_data_stream1, file_data_stream2;
   string new_line1, new_cell1, new_line2, new_cell2;

   // open both files into file streams
   read_file1.open( input_file1.c_str() );
   read_file2.open( input_file2.c_str() );

  // read in each line of the first input file
   while(getline(read_file1, new_line1)) {
      // also read the second input file
      getline(read_file2, new_line2);

      // add current row to stringstream
      file_data_stream1 << new_line1;
      file_data_stream2 << new_line2;

      // parse stringstream for first file on tab to get fields
      while(getline(file_data_stream1, new_cell1,'\t')) {
         // also parse stringstream for second file
          getline(file_data_stream2, new_cell2,'\t');

         // the data for the same line of both files is now parsed

      }
   }

Would that read both files in registration? Does getline() have an iterator somewhere I could access to instruct it to read a specific line? Am I going about this in the wrong way altogher?

I could always just read in one file and store it, but that doesn't seem very efficient in this case.

LMHmedchem