center.cpp

// https://stackoverflow.com/questions/14861018/center-text-in-fixed-width-field-with-stream-manipulators-in-c/14861289#14861289
#include <string>
#include <iostream>
#include <iomanip>

template<typename charT, typename traits = std::char_traits<charT> >
class center_helper {
  std::basic_string<charT, traits> str_;
public:
  center_helper(std::basic_string<charT, traits> str) : str_(str) {}
  template<typename a, typename b>
  friend std::basic_ostream<a, b>& operator<<(std::basic_ostream<a, b>& s, const center_helper<a, b>& c);
};

template<typename charT, typename traits = std::char_traits<charT> >
center_helper<charT, traits> centered(std::basic_string<charT, traits> str) {
  return center_helper<charT, traits>(str);
}

center_helper<std::string::value_type, std::string::traits_type> centered(const std::string& str) {
  return center_helper<std::string::value_type, std::string::traits_type>(str);
}

template<typename charT, typename traits>
std::basic_ostream<charT, traits>& operator<<(std::basic_ostream<charT, traits>& s, const center_helper<charT, traits>& c) {
  std::streamsize w = s.width();
  if (w > c.str_.length()) {
    std::streamsize left = (w + c.str_.length()) / 2;
    s.width(left);
    s << c.str_;
    s.width(w - left);
    s << "";
  } else {
    s << c.str_;
  }
  return s;
}