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Class template period

boost::date_time::period — Provides generalized period type useful in date-time systems.


// In header: <boost/date_time/period.hpp>

template<typename point_rep, typename duration_rep> 
class period {
  // types
  typedef point_rep    point_type;   
  typedef duration_rep duration_type;

  // construct/copy/destruct
  period(point_rep, point_rep);
  period(point_rep, duration_rep);

  // public member functions
  point_rep begin() const;
  point_rep end() const;
  point_rep last() const;
  duration_rep length() const;
  bool is_null() const;
  bool operator==(const period &) const;
  bool operator<(const period &) const;
  void shift(const duration_rep &) ;
  void expand(const duration_rep &) ;
  bool contains(const point_rep &) const;
  bool contains(const period &) const;
  bool intersects(const period &) const;
  bool is_adjacent(const period &) const;
  bool is_before(const point_rep &) const;
  bool is_after(const point_rep &) const;
  period intersection(const period &) const;
  period merge(const period &) const;
  period span(const period &) const;


This template uses a class to represent a time point within the period and another class to represent a duration. As a result, this class is not appropriate for use when the number and duration representation are the same (eg: in the regular number domain).

A period can be specified by providing either the begining point and a duration or the begining point and the end point( end is NOT part of the period but 1 unit past it. A period will be "invalid" if either end_point <= begin_point or the given duration is <= 0. Any valid period will return false for is_null().

Zero length periods are also considered invalid. Zero length periods are periods where the begining and end points are the same, or, the given duration is zero. For a zero length period, the last point will be one unit less than the begining point.

In the case that the begin and last are the same, the period has a length of one unit.

The best way to handle periods is usually to provide a begining point and a duration. So, day1 + 7 days is a week period which includes all of the first day and 6 more days (eg: Sun to Sat).

period public construct/copy/destruct

  1. period(point_rep first_point, point_rep end_point);
    create a period from begin to last eg: [begin,end)

    If end <= begin then the period will be invalid

  2. period(point_rep first_point, duration_rep len);
    create a period as [begin, begin+len)

    If len is <= 0 then the period will be invalid

period public member functions

  1. point_rep begin() const;
    Return the first element in the period.
  2. point_rep end() const;
    Return one past the last element.
  3. point_rep last() const;
    Return the last item in the period.
  4. duration_rep length() const;
    Return the length of the period.
  5. bool is_null() const;
    True if period is ill formed (length is zero or less).
  6. bool operator==(const period & rhs) const;
    Equality operator.
  7. bool operator<(const period & rhs) const;
    Strict as defined by rhs.last <= lhs.last.
  8. void shift(const duration_rep & d) ;
    Shift the start and end by the specified amount.
  9. void expand(const duration_rep & d) ;

    Expands the size of the period by the duration on both ends.

    So before expand

     ^   ^   ^   ^   ^   ^  ^
     1   2   3   4   5   6  7

    After expand(2)

     ^   ^   ^   ^   ^   ^  ^
     1   2   3   4   5   6  7

  10. bool contains(const point_rep & point) const;
    True if the point is inside the period, zero length periods contain no points.
  11. bool contains(const period & other) const;
    True if this period fully contains (or equals) the other period.
  12. bool intersects(const period & other) const;
    True if the periods overlap in any way.
  13. bool is_adjacent(const period & other) const;
    True if periods are next to each other without a gap.
  14. bool is_before(const point_rep & point) const;
    True if all of the period is prior to the passed point or end <= t.
  15. bool is_after(const point_rep & point) const;
    True if all of the period is prior or t < start.
  16. period intersection(const period & other) const;
    Returns the period of intersection or invalid range no intersection.
  17. period merge(const period & other) const;
    Returns the union of intersecting periods -- or null period.
  18. period span(const period & other) const;
    Combine two periods with earliest start and latest end.

    Combines two periods and any gap between them such that start = min(p1.start, p2.start) end = max(p1.end , p2.end)