[3408] | 1 | #ifndef DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__ |
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| 2 | #define DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__ |
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| 3 | |
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| 4 | /* Copyright (c) 2002,2003 CrystalClear Software, Inc. |
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| 5 | * Use, modification and distribution is subject to the |
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| 6 | * Boost Software License, Version 1.0. (See accompanying |
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| 7 | * file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt) |
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| 8 | * Author: Jeff Garland |
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| 9 | * $Date: 2008-11-12 14:37:53 -0500 (Wed, 12 Nov 2008) $ |
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| 10 | */ |
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| 11 | |
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| 12 | /*! @file local_time_adjustor.hpp |
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| 13 | Time adjustment calculations for local times |
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| 14 | */ |
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| 15 | |
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| 16 | #include <stdexcept> |
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| 17 | #include <boost/throw_exception.hpp> |
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| 18 | #include <boost/date_time/compiler_config.hpp> |
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| 19 | #include <boost/date_time/date_generators.hpp> |
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| 20 | #include <boost/date_time/dst_rules.hpp> |
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| 21 | #include <boost/date_time/time_defs.hpp> // boost::date_time::dst_flags |
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| 22 | #include <boost/date_time/special_defs.hpp> // not_a_date_time |
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| 23 | |
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| 24 | namespace boost { |
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| 25 | namespace date_time { |
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| 26 | |
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| 27 | |
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| 28 | //! Provides a base offset adjustment from utc |
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| 29 | template<class time_duration_type, |
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| 30 | short hours, unsigned short minutes = 0> |
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| 31 | class utc_adjustment |
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| 32 | { |
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| 33 | public: |
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| 34 | static time_duration_type local_to_utc_base_offset() |
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| 35 | { |
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| 36 | time_duration_type td(hours,minutes,0); |
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| 37 | return td.invert_sign(); |
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| 38 | } |
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| 39 | static time_duration_type utc_to_local_base_offset() |
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| 40 | { |
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| 41 | return time_duration_type(hours,minutes,0); |
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| 42 | } |
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| 43 | }; |
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| 44 | |
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| 45 | |
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| 46 | |
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| 47 | //! Allow sliding utc adjustment with fixed dst rules |
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| 48 | template<class time_type, class dst_rules> |
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| 49 | class dynamic_local_time_adjustor : public dst_rules |
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| 50 | { |
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| 51 | public: |
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| 52 | typedef typename time_type::time_duration_type time_duration_type; |
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| 53 | typedef typename time_type::date_type date_type; |
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| 54 | |
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| 55 | dynamic_local_time_adjustor(time_duration_type utc_offset) : |
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| 56 | utc_offset_(utc_offset) |
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| 57 | {} |
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| 58 | |
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| 59 | //! Presumes local time |
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| 60 | time_duration_type utc_offset(bool is_dst) |
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| 61 | { |
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| 62 | if (is_dst) { |
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| 63 | return utc_offset_ + this->dst_offset(); |
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| 64 | } |
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| 65 | else { |
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| 66 | return utc_offset_; |
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| 67 | } |
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| 68 | |
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| 69 | } |
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| 70 | private: |
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| 71 | time_duration_type utc_offset_; |
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| 72 | |
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| 73 | }; |
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| 74 | |
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| 75 | |
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| 76 | |
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| 77 | //! Embed the rules for local time adjustments at compile time |
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| 78 | template<class time_type, class dst_rules, class utc_offset_rules> |
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| 79 | class static_local_time_adjustor: public dst_rules, public utc_offset_rules |
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| 80 | { |
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| 81 | public: |
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| 82 | typedef typename time_type::time_duration_type time_duration_type; |
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| 83 | typedef typename time_type::date_type date_type; |
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| 84 | |
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| 85 | //! Calculates the offset from a utc time to local based on dst and utc offset |
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| 86 | /*! @param t UTC time to calculate offset to local time |
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| 87 | * This adjustment depends on the following observations about the |
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| 88 | * workings of the DST boundary offset. Since UTC time labels are |
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| 89 | * monotonically increasing we can determine if a given local time |
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| 90 | * is in DST or not and therefore adjust the offset appropriately. |
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| 91 | * |
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| 92 | * The logic is as follows. Starting with UTC time use the offset to |
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| 93 | * create a label for an non-dst adjusted local time. Then call |
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| 94 | * dst_rules::local_is_dst with the non adjust local time. The |
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| 95 | * results of this function will either unabiguously decide that |
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| 96 | * the initial local time is in dst or return an illegal or |
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| 97 | * ambiguous result. An illegal result only occurs at the end |
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| 98 | * of dst (where labels are skipped) and indicates that dst has |
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| 99 | * ended. An ambiguous result means that we need to recheck by |
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| 100 | * making a dst adjustment and then rechecking. If the dst offset |
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| 101 | * is added to the utc time and the recheck proves non-ambiguous |
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| 102 | * then we are past the boundary. If it is still ambiguous then |
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| 103 | * we are ahead of the boundary and dst is still in effect. |
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| 104 | * |
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| 105 | * TODO -- check if all dst offsets are positive. If not then |
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| 106 | * the algorithm needs to check for this and reverse the |
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| 107 | * illegal/ambiguous logic. |
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| 108 | */ |
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| 109 | static time_duration_type utc_to_local_offset(const time_type& t) |
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| 110 | { |
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| 111 | //get initial local time guess by applying utc offset |
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| 112 | time_type initial = t + utc_offset_rules::utc_to_local_base_offset(); |
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| 113 | time_is_dst_result dst_flag = |
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| 114 | dst_rules::local_is_dst(initial.date(), initial.time_of_day()); |
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| 115 | switch(dst_flag) { |
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| 116 | case is_in_dst: return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
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| 117 | case is_not_in_dst: return utc_offset_rules::utc_to_local_base_offset(); |
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| 118 | case invalid_time_label:return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
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| 119 | case ambiguous: { |
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| 120 | time_type retry = initial + dst_rules::dst_offset(); |
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| 121 | dst_flag = dst_rules::local_is_dst(retry.date(), retry.time_of_day()); |
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| 122 | //if still ambibuous then the utc time still translates to a dst time |
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| 123 | if (dst_flag == ambiguous) { |
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| 124 | return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
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| 125 | } |
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| 126 | // we are past the dst boundary |
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| 127 | else { |
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| 128 | return utc_offset_rules::utc_to_local_base_offset(); |
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| 129 | } |
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| 130 | } |
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| 131 | }//case |
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| 132 | //TODO better exception type |
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| 133 | boost::throw_exception(std::out_of_range("Unreachable case")); |
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| 134 | BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach |
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| 135 | } |
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| 136 | |
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| 137 | //! Get the offset to UTC given a local time |
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| 138 | static time_duration_type local_to_utc_offset(const time_type& t, |
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| 139 | date_time::dst_flags dst=date_time::calculate) |
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| 140 | { |
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| 141 | switch (dst) { |
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| 142 | case is_dst: |
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| 143 | return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset(); |
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| 144 | case not_dst: |
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| 145 | return utc_offset_rules::local_to_utc_base_offset(); |
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| 146 | case calculate: |
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| 147 | time_is_dst_result res = |
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| 148 | dst_rules::local_is_dst(t.date(), t.time_of_day()); |
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| 149 | switch(res) { |
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| 150 | case is_in_dst: return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset(); |
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| 151 | case is_not_in_dst: return utc_offset_rules::local_to_utc_base_offset(); |
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| 152 | case ambiguous: return utc_offset_rules::local_to_utc_base_offset(); |
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| 153 | case invalid_time_label: break; |
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| 154 | } |
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| 155 | } |
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| 156 | boost::throw_exception(std::out_of_range("Time label invalid")); |
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| 157 | BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach |
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| 158 | } |
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| 159 | |
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| 160 | |
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| 161 | private: |
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| 162 | |
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| 163 | }; |
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| 164 | |
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| 165 | void dummy_to_prevent_msvc6_ice(); //why ask why? |
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| 166 | |
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| 167 | //! Template that simplifies the creation of local time calculator |
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| 168 | /*! Use this template to create the timezone to utc convertors as required. |
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| 169 | * |
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| 170 | * This class will also work for other regions that don't use dst and |
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| 171 | * have a utc offset which is an integral number of hours. |
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| 172 | * |
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| 173 | * <b>Template Parameters</b> |
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| 174 | * -time_type -- Time class to use |
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| 175 | * -utc_offset -- Number hours local time is adjust from utc |
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| 176 | * -use_dst -- true (default) if region uses dst, false otherwise |
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| 177 | * For example: |
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| 178 | * @code |
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| 179 | * //eastern timezone is utc-5 |
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| 180 | typedef date_time::local_adjustor<ptime, -5, us_dst> us_eastern; |
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| 181 | typedef date_time::local_adjustor<ptime, -6, us_dst> us_central; |
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| 182 | typedef date_time::local_adjustor<ptime, -7, us_dst> us_mountain; |
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| 183 | typedef date_time::local_adjustor<ptime, -8, us_dst> us_pacific; |
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| 184 | typedef date_time::local_adjustor<ptime, -7, no_dst> us_arizona; |
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| 185 | @endcode |
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| 186 | |
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| 187 | */ |
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| 188 | template<class time_type, short utc_offset, class dst_rule> |
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| 189 | class local_adjustor |
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| 190 | { |
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| 191 | public: |
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| 192 | typedef typename time_type::time_duration_type time_duration_type; |
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| 193 | typedef typename time_type::date_type date_type; |
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| 194 | typedef static_local_time_adjustor<time_type, |
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| 195 | dst_rule, |
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| 196 | utc_adjustment<time_duration_type, |
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| 197 | utc_offset> > dst_adjustor; |
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| 198 | //! Convert a utc time to local time |
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| 199 | static time_type utc_to_local(const time_type& t) |
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| 200 | { |
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| 201 | time_duration_type td = dst_adjustor::utc_to_local_offset(t); |
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| 202 | return t + td; |
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| 203 | } |
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| 204 | //! Convert a local time to utc |
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| 205 | static time_type local_to_utc(const time_type& t, |
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| 206 | date_time::dst_flags dst=date_time::calculate) |
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| 207 | { |
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| 208 | time_duration_type td = dst_adjustor::local_to_utc_offset(t, dst); |
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| 209 | return t + td; |
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| 210 | } |
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| 211 | }; |
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| 212 | |
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| 213 | |
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| 214 | } } //namespace date_time |
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| 215 | |
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| 216 | |
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| 217 | |
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| 218 | #endif |
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