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C++ Cookbook
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C++ Cookbook

by D. Ryan Stephens, Christopher Diggins, Jonathan Turkanis, Jeff Cogswell
November 2005
Beginner to intermediate content levelBeginner to intermediate
594 pages
16h 23m
English
O'Reilly Media, Inc.
Content preview from C++ Cookbook

15.6. Initializing a Sequence with Comma-Separated Values

Problem

You want to initialize a sequence with a comma-delimited set of values, like you can with a built-in array.

Solution

You can use a comma-initialization syntax on standard sequences (such as vector and list) by defining a helper class and overloading the comma operator for it as demonstrated in Example 15-6.

Example 15-6. Utilities for comma initialization of standard sequences

#include <vector>
#include <iostream>
#include <iterator>
#include <algorithm>

using namespace std; 

template<class Seq_T>
struct comma_helper
{
  typedef typename Seq_T::value_type value_type;
  explicit comma_helper(Seq_T& x) : m(x) { }
  comma_helper& operator=(const value_type& x) {
    m.clear();
    return operator+=(x);
  }
  comma_helper& operator+=(const value_type& x) {
    m.push_back(x);
    return *this;
  }
  Seq_T& m;
};

template<typename Seq_T>
comma_helper<Seq_T>
initialize(Seq_T& x) {
  return comma_helper<Seq_T>(x);
}

template<class Seq_T, class Scalar_T>
comma_helper<Seq_T>&
operator,(comma_helper<Seq_T>& h, Scalar_T x) {
  h += x;
  return h;
}

int main() {
  vector v;
  int a = 2;
  int b = 5;
  initialize(v) = 0, 1, 1, a, 3, b, 8, 13;
  cout << v[3] << endl; // outputs 2
  system("pause");
  return EXIT_SUCCESS;
}

Discussion

Often time standard sequences are initialized by calling a push_back member function several times. Since this is somewhat repetitive, I wrote a function, initialize, which helps eliminate the tedium, by enabling comma initialization à la built-in arrays. ...

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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page