ceph/src/boost/libs/date_time/example/gregorian/month_add.cpp

   1 /* Simple program that uses the gregorian calendar to progress by exactly
   2  * one month, regardless of how many days are in that month.
   3  *
   4  * This method can be used as an alternative to iterators
   5  */
   6
   7 #include "boost/date_time/gregorian/gregorian.hpp"
   8 #include <iostream>
   9
  10 int
  11 main()
  12 {
  13
  14   using namespace boost::gregorian;
  15
  16   date d = day_clock::local_day();
  17   date d2 = d + months(1);
  18   date d3 = d - months(1);
  19   std::cout << "Today is: " << to_simple_string(d) << ".\n"
  20             << "One month from today will be: " << to_simple_string(d2) << ".\n"
  21             << "One month ago was: " << to_simple_string(d3)
  22             << std::endl;
  23   std::cout << "******** Warning read this ***********************\n";
  24   std::cout << "Be aware that adding a month is not exactly like regular numeric math.\n"
  25             << "Addition/Subtraction of months will 'snap to the end' of a month that\n"
  26             << "is shorter than the current month.  For example consider "
  27             << "Jan 31, 2004 + (1 month)\n";
  28   date d4(2004, Jan, 31);
  29   date d5 = d4 + months(1);
  30   std::cout << "Result is: " << to_simple_string(d5)
  31             << std::endl;
  32
  33   std::cout << "\nSo what does this mean?  It means the result of adding months is order\n"
  34             << "dependent, non-commutative, and may create problems for applications.\n"
  35             << "Consider: \n"
  36             << "Jan 30, 2004 + (1 month) + (1 month) != Jan 30, 2004 + (2 months)\n"
  37             << "Why not? Because Jan 30, 2004 + 1 month is Feb 29 + 1 month is Mar 31st.\n"
  38             << "while Jan 30, 2004 + 2 months is Mar 30th.\n"
  39             << "All of this clears up as long as all the starting dates before the 28th of\n"
  40             << "the month -- then all the behavior follows classical mathematical rules.\n";
  41
  42   date d6(2004, Jan, 30);
  43   date d7 = d6 + months(1) + months(1);
  44   date d8 = d6 + months(2);
  45   std::cout << "2004-01-30 + (1 month) + (1 month) is: " << to_simple_string(d7) << ".\n"
  46             << "2004-01-30 + (2 months) is: " << to_simple_string(d8)
  47                         << std::endl;
  48
  49   return 0;
  50 }
  51
  52 /*  Copyright 2001-2005: CrystalClear Software, Inc
  53  *  http://www.crystalclearsoftware.com
  54  *
  55  *  Subject to the Boost Software License, Version 1.0.
  56  * (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
  57  */
  58