regexIterator.cpp

#include <regex>

#include <iostream>
#include <string>
#include <map>
#include <unordered_map>

int main(){

  std::cout << '\n';

  // Bjarne Stroustrup about C++11 on http://www.stroustrup.com/C++11FAQ.html
  std::string text{"That's a (to me) amazingly frequent question. It may be the most frequently asked question. Surprisingly, C++11 feels like a new language: The pieces just fit together better than they used to and I find a higher-level style of programming more natural than before and as efficient as ever."};

  // regular expression for a word
  std::regex wordReg(R"(\w+)");

  // get all words from text
  std::sregex_iterator wordItBegin(text.begin(), text.end(), wordReg);
  const std::sregex_iterator wordItEnd;

  // use a map to count the wourds
  std::unordered_map<std::string, std::size_t> allWords;

  // count the words
  for (; wordItBegin != wordItEnd;++wordItBegin){
    ++allWords[wordItBegin->str()];
  }

  for (auto wordIt: allWords) std::cout << "(" << wordIt.first << ":" << wordIt.second << ")" ;

  std::cout << '\n';

}