Is there something akin to a looping (circular) iterator?

Question

I'm wondering if there's some sort of iterator that can iterate over values in a std::string, starting over from the beginning when it reaches the end. In other words, this object would iterate indefinitely, spitting out the same sequence of values over and over again.

Thanks!

Check this answer http://stackoverflow.com/a/1782262/1762344 — Evgeny Panasyuk, Nov 07 '12 at 22:14
@Evgeny the increment() function in that answer looks questionable. If advanced to end, it should probably immediately jump back to begin. — Yakk - Adam Nevraumont, Nov 07 '12 at 22:22
@Yakk - yes, I have just looked to it - I agree with you, it should jump to begin immediately. Otherwise it is possible end dereference. Though author of message said: "This probably doesn't compile but should get you started." — Evgeny Panasyuk, Nov 07 '12 at 22:25
http://stackoverflow.com/questions/1782019/easiest-way-to-make-a-cyclic-iterator — adripanico, Nov 07 '12 at 22:25

sehe · Accepted Answer · 2013-10-23T12:08:14.070

A generator function could be that. Boost Iterator has the iterator adaptor for that:

http://www.boost.org/doc/libs/1_52_0/libs/utility/generator_iterator.htm

A sample: http://coliru.stacked-crooked.com/a/267279405be9289d

#include <iostream>
#include <functional>
#include <algorithm>
#include <iterator>
#include <boost/generator_iterator.hpp>

int main()
{
  const std::string data = "hello";
  auto curr = data.end();

  std::function<char()> gen = [curr,data]() mutable -> char
  { 
      if (curr==data.end())
          curr = data.begin();
      return *curr++;
  };

  auto it = boost::make_generator_iterator(gen);
  std::copy_n(it, 35, std::ostream_iterator<char>(std::cout, ";"));
}

added a _short_ sample (also using `copy_n` on [LWS](http://liveworkspace.org/code/2e09ce186cca5785742f7d7b25c005d0)) — sehe, Nov 07 '12 at 22:31

Is there something akin to a looping (circular) iterator?

1 Answers1