Question

Hi I have a text file which contains some numerical data. Of that text file ONLY the lines
14 to 100 have to be read into my C++ program. Each of these lines contain three numbers corresponding to x,y,z coordinates of a point. Thus, coordinates are given for 87 points in all.

I want to put these numbers into the arrays xp[87] yp[87] and zp[87].

How do I perform this?

Uptil now I have been used to the following

ifstream readin(argv[1])//Name of the text file 

for (int i=0; i<=86; ++i)
{
readin>>xp[i]>>yp[i]>>zp[i];
}

But this technique works only for those files which contain 87 lines and the data to be read starts from the first line itself.

In the present case I want to ignore ALL lines before line 14 and ALL lines after line 100

Answer 1

Read line by line, for most flexibility in your format:

#include <fstream>
#include <sstream>
#include <string>

std::ifstream infile("thefile.txt");
std::string line;

unsigned int count = 0;

while (std::getline(infile, line))
{
  ++count;
  if (count > 100) { break; }    // done
  if (count < 14)  { continue; } // too early

  std::istringstream iss(line);
  if (!(iss >> x[count - 14] >> y[count - 14] >> z[count - 14]))
  {
    // error
  }
}

// all done