Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Header <boost/icl/gregorian.hpp>

namespace boost {
  namespace icl {
    template<> struct difference_type_of<boost::gregorian::date>;
    template<> struct has_difference<boost::gregorian::date>;
    template<> struct has_difference<boost::gregorian::date_duration>;
    template<> struct identity_element<boost::gregorian::date_duration>;
    template<> struct is_discrete<boost::gregorian::date>;
    template<> struct is_discrete<boost::gregorian::date_duration>;
    template<> struct size_type_of<boost::gregorian::date>;
    template<> struct size_type_of<boost::gregorian::date_duration>;
    boost::gregorian::date operator++(boost::gregorian::date & x);
    boost::gregorian::date operator--(boost::gregorian::date & x);
    boost::gregorian::date_duration 
    operator++(boost::gregorian::date_duration & x);
    boost::gregorian::date_duration 
    operator--(boost::gregorian::date_duration & x);
  }
}