Introduction -- Header -- Construction -- Accessors -- Operators -- Additional Duration Types Introduction The class boost::gregorian::date_duration is a simple day count used for arithmetic with gregorian::date. A duration can be either positive or negative. As of version 1_32 the date_duration class has been typedef'd as days in the boost::gregorian namespace. Throughout the examples you will find days used instead of date_duration. Header #include "boost/date_time/gregorian/gregorian.hpp" //include all types plus i/o or #include "boost/date_time/gregorian/gregorian_types.hpp" //no i/o just types Construction Syntax Description Example date_duration(long) Create a duration count. date_duration dd(3); //3 days days(special_values sv) Constructor for infinities, not-a-date-time, max_date_time, and min_date_time days dd1(neg_infin); days dd2(pos_infin); days dd3(not_a_date_time); days dd4(max_date_time); days dd5(min_date_time); Accessors Syntax Description Example long days() const Get the day count. date_duration dd(3); dd.days() --> 3 bool is_negative() const True if number of days is less than zero. date_duration dd(-1); dd.is_negative() --> true static date_duration unit() Return smallest possible unit of duration type. date_duration::unit() --> date_duration(1) bool is_special() const Returns true if days is any special_value days dd(pos_infin); days dd2(not_a_date_time); days dd3(25); dd.is_special(); // --> true dd2.is_special(); // --> true dd3.is_special(); // --> false Operators Syntax Description Example operator<<, operator>> Streaming operators. Note: As of version 1.33, streaming operations have been greatly improved. See Date Time IO System for more details (including exceptions and error conditions). date d(not_a_date_time); stringstream ss("2002-Jan-01"); ss >> d; std::cout << d; // "2002-Jan-01" operator==, operator!=, operator>, operator<, operator>=, operator<= A full complement of comparison operators dd1 == dd2, etc date_duration operator+(date_duration) const Add date durations. date_duration dd1(3); date_duration dd2(5); date_duration dd3 = dd1 + dd2; date_duration operator-(date_duration) const Subtract durations. date_duration dd1(3); date_duration dd2(5); date_duration dd3 = dd1 - dd2; Additional Duration Types These additional types are logical representations of spans of days. Syntax Description Example months(int num_of_months) A logical month representation. Depending on the usage, this months object may cover a span of 28 to 31 days. The objects also use a snap to end-of-month behavior when used in conjunction with a date that is the last day of a given month. WARNING: this behavior may lead to unexpected results. See: Reversibility of Operations Pitfall for complete details and alternatives. months single(1); date leap_year(2004,Jan,31); date norm_year(2005,Jan,31); leap_year + single; // => 2004-Feb-29 norm_year + single; // => 2005-Feb-28 date(2005,Jan,1) + single; // => 2005-Feb-01 date(2005,Feb,1) + single; // => 2005-Mar-01 date(2005,Feb,28) + single; // => 2005-Mar-31 years(int num_of_years) A logical representation of a year. The years object has the same behavior as the months objects with regards to the end-of-the-month. years single(1); date(2003,Feb,28) + single; // results in => 2004-Feb-29 date(2004,Feb,29) + single; // results in => 2005-Feb-28 weeks(int num_of_weeks) A duration type representing a number of n * 7 days. weeks single(1); date(2005,Jan,1) + single; // => 2005-Jan-08