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
main()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
59