C++ Cookbook

4.19. Add Margins to a Text File

Problem

Given a text file, you want to add margins to it. In other words, you want to pad either side of each line with some character so that each line is the same width.

Solution

Example 4-28 shows how to add margins to a file using streams, strings, and the getline function template.

Example 4-28. Adding margins to a text file

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>

using namespace std;
const static char PAD_CHAR = '.';

// addMargins takes two streams and two numbers. The streams are for
// input and output. The first of the two numbers represents the
// left margin width (i.e., the number of spaces to insert at the 
// beginning of every line in the file). The second number represents
// the total line width to pad to.
void addMargins(istream& in, ostream& out,
                int left, int right) {

   string tmp;

   while (!in.eof()) {
      getline(in, tmp, '\n');                     // getline is defined
                                                  // in <string>
      tmp.insert(tmp.begin(), left, PAD_CHAR);
      rpad(tmp, right, PAD_CHAR);                 // rpad from Recipe
                                                  // 4.2
      out << tmp << '\n';
   }
}

int main(int argc, char** argv) {

   if (argc < 3)
      return(EXIT_FAILURE);

   ifstream in(argv[1]);
   ofstream out(argv[2]);

   if (!in || !out)
      return(EXIT_FAILURE);

   int left = 8;
   int right = 72;

   if (argc == 5) {
      left = atoi(argv[3]);
      right = atoi(argv[4]);
   }

   addMargins(in, out, left, right);

   out.close();

   if (out)
      return(EXIT_SUCCESS);
   else
      return(EXIT_FAILURE);
}

This example makes a few assumptions about the format of the incoming text, ...