59 lines
2.3 KiB
C++
59 lines
2.3 KiB
C++
/* Simple program that uses the gregorian calendar to progress by exactly
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* one month, regardless of how many days are in that month.
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*
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* This method can be used as an alternative to iterators
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*/
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#include "boost/date_time/gregorian/gregorian.hpp"
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#include <iostream>
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int
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main()
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{
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using namespace boost::gregorian;
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date d = day_clock::local_day();
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date d2 = d + months(1);
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date d3 = d - months(1);
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std::cout << "Today is: " << to_simple_string(d) << ".\n"
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<< "One month from today will be: " << to_simple_string(d2) << ".\n"
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<< "One month ago was: " << to_simple_string(d3)
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<< std::endl;
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std::cout << "******** Warning read this ***********************\n";
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std::cout << "Be aware that adding a month is not exactly like regular numeric math.\n"
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<< "Addition/Subtraction of months will 'snap to the end' of a month that\n"
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<< "is shorter than the current month. For example consider "
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<< "Jan 31, 2004 + (1 month)\n";
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date d4(2004, Jan, 31);
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date d5 = d4 + months(1);
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std::cout << "Result is: " << to_simple_string(d5)
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<< std::endl;
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std::cout << "\nSo what does this mean? It means the result of adding months is order\n"
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<< "dependent, non-commutative, and may create problems for applications.\n"
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<< "Consider: \n"
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<< "Jan 30, 2004 + (1 month) + (1 month) != Jan 30, 2004 + (2 months)\n"
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<< "Why not? Because Jan 30, 2004 + 1 month is Feb 29 + 1 month is Mar 31st.\n"
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<< "while Jan 30, 2004 + 2 months is Mar 30th.\n"
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<< "All of this clears up as long as all the starting dates before the 28th of\n"
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<< "the month -- then all the behavior follows classical mathematical rules.\n";
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date d6(2004, Jan, 30);
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date d7 = d6 + months(1) + months(1);
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date d8 = d6 + months(2);
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std::cout << "2004-01-30 + (1 month) + (1 month) is: " << to_simple_string(d7) << ".\n"
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<< "2004-01-30 + (2 months) is: " << to_simple_string(d8)
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<< std::endl;
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return 0;
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}
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/* Copyright 2001-2005: CrystalClear Software, Inc
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* http://www.crystalclearsoftware.com
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*
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* Subject to the Boost Software License, Version 1.0.
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* (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
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*/
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