C++ Cookbook

4.23. Reading a Comma-Separated Text File

Problem

You want to read in a text file that is delimited by commas and new lines (or any other pair of delimiters for that matter). Records are delimited by one character, and fields within a record are delimited by another. For example, a comma-separated text file of employee information may look like the following:

Smith, Bill, 5/1/2002, Active
Stanford, John, 4/5/1999, Inactive

Such files are usually interim storage for data sets exported from spreadsheets, databases, or other file formats.

Solution

See Example 4-32 for how to do this. If you read the text into strings one contiguous chunk at a time using getline (the function template defined in <string>) you can use the split function I presented in Recipe 4.6 to parse the text and put it in a data structure, in this case, a vector.

Example 4-32. Reading in a delimited file

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

using namespace std;

void split(const string& s, char c,
           vector<string>& v) {
   int i = 0;
   int j = s.find(c);

   while (j >= 0) {
      v.push_back(s.substr(i, j-i));
      i = ++j;
      j = s.find(c, j);

      if (j < 0) {
         v.push_back(s.substr(i, s.length()));
      }
   }
}

void loadCSV(istream& in, vector<vector<string>*>& data) {

   vector<string>* p = NULL;
   string tmp;

   while (!in.eof()) {
      getline(in, tmp, '\n');                     // Grab the next line

      p = new vector<string>();
      split(tmp, ',', *p);                        // Use split from
                                                  // Recipe 4.7 data.push_back(p); cout << tmp << '\n'; tmp.clear(); } } int main(int ...