C++ Cookbook

4.21. Squeeze Whitespace to Single Spaces in a Text File

Problem

You have a text file with whitespace of varying lengths in it, and you want to reduce every occurrence of a contiguous span of whitespace characters to a single space.

Solution

Use the operator>> function template, defined in <string>, to read in continuous chunks of non-whitespace from a stream into a string. Then use its counterpart, operator<<, to write each of these chunks to an output stream, and append a single character after each one. Example 4-30 gives a short example of this technique.

Example 4-30. Squeezing whitespace to single spaces

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

using namespace std;

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);

   string tmp;

   in >> tmp;          // Grab the first word
   out << tmp;         // Dump it to the output stream

   while (in >> tmp) { // operator>> ignores whitespace, so all I have
      out << ' ';      // to do is add a space and each chunk of non-
      out << tmp;      // whitespace
   }

   out.close();
}

Discussion

This is a simple thing to do if you take advantage of streams and strings. Even if you have to implement a variation of this—for example, you may want to preserve new lines—the same facilities do the trick. If you want to add new lines, you can use the solution presented in Recipe 4.16 to insert them in the right place.

See Also

Recipe 4.15 and Recipe 4.16