C++14: Standard user-defined literals

C++14 defined several standard user-defined literals:

operator""if          imaginary float      std::literals::complex_literals

operator""I           imaginary double  std::literals::complex_literals

operator""il          imaginary long      std::literals::complex_literals

operator""h          hours                      std::literals::chrono_literals

operator""min      minutes                  std::chrono::duration

operator""s          seconds                   std::chrono::duration

operator""ms       milliseconds           std::chrono::duration

operator""us        microseconds         std::chrono::duration

operator""ns        nanoseconds          std::chrono::duration

operator""s          string                      std::literals::string_literals

Here is an example:

#include <chrono>
#include <complex>
#include <iostream>

int main()
{
  using namespace std::complex_literals;
  std::cout << 1.1if << " ";
  std::cout << 2.2i  << " ";
  std::cout << 3il   << " ";

  using namespace std::chrono_literals;
  std::cout << std::chrono::seconds    (4h  ).count() << " ";
  std::cout << std::chrono::seconds    (5min).count() << " ";
  std::cout << std::chrono::seconds    (6s  ).count() << " ";
  std::cout << std::chrono::nanoseconds(7ms ).count() << " ";
  std::cout << std::chrono::nanoseconds(8us ).count() << " ";
  std::cout << std::chrono::nanoseconds(9ns ).count() << " ";

  using namespace std::string_literals;
  std::cout << "Hello"s << " ";

  std::cout << std::endl;
  return 0;
}
// Output: (0,1.1) (0,2.2) (0,3) 14400 300 6 7000000 8000 9 Hello

Reference: http://en.cppreference.com/w/cpp/language/user_literal