[857] | 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 or http://www.boost.org/LICENSE-1.0)
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| 8 | * Author: Jeff Garland
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| 9 | * $Date: 2003/11/23 03:29:56 $
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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 "boost/date_time/date_generators.hpp"
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| 17 | #include "boost/date_time/dst_rules.hpp"
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| 18 | #include <stdexcept>
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| 19 |
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| 20 | namespace boost {
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| 21 | namespace date_time {
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| 22 |
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| 23 |
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| 24 | //! Provides a base offset adjustment from utc
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| 25 | template<class time_duration_type,
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| 26 | short hours, unsigned short minutes = 0>
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| 27 | class utc_adjustment
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| 28 | {
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| 29 | public:
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| 30 | static time_duration_type local_to_utc_base_offset()
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| 31 | {
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| 32 | time_duration_type td(hours,minutes,0);
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| 33 | return td.invert_sign();
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| 34 | }
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| 35 | static time_duration_type utc_to_local_base_offset()
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| 36 | {
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| 37 | return time_duration_type(hours,minutes,0);
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| 38 | }
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| 39 | };
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| 40 |
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| 41 |
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| 42 |
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| 43 | //! Allow sliding utc adjustment with fixed dst rules
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| 44 | template<class time_type, class dst_rules>
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| 45 | class dynamic_local_time_adjustor : public dst_rules
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| 46 | {
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| 47 | public:
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| 48 | typedef typename time_type::time_duration_type time_duration_type;
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| 49 | typedef typename time_type::date_type date_type;
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| 50 |
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| 51 | dynamic_local_time_adjustor(time_duration_type utc_offset) :
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| 52 | utc_offset_(utc_offset)
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| 53 | {}
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| 54 |
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| 55 | //! Presumes local time
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| 56 | time_duration_type utc_offset(bool is_dst)
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| 57 | {
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| 58 | if (is_dst) {
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| 59 | return utc_offset_ + this->dst_offset();
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| 60 | }
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| 61 | else {
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| 62 | return utc_offset_;
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| 63 | }
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| 64 |
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| 65 | }
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| 66 | private:
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| 67 | time_duration_type utc_offset_;
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| 68 |
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| 69 | };
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| 70 |
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| 71 |
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| 72 |
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| 73 | //! Embed the rules for local time adjustments at compile time
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| 74 | template<class time_type, class dst_rules, class utc_offset_rules>
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| 75 | class static_local_time_adjustor: public dst_rules, public utc_offset_rules
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| 76 | {
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| 77 | public:
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| 78 | typedef typename time_type::time_duration_type time_duration_type;
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| 79 | typedef typename time_type::date_type date_type;
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| 80 |
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| 81 | //! Calculates the offset from a utc time to local based on dst and utc offset
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| 82 | /*! @param t UTC time to calculate offset to local time
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| 83 | * This adjustment depends on the following observations about the
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| 84 | * workings of the DST boundary offset. Since UTC time labels are
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| 85 | * monotonically increasing we can determine if a given local time
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| 86 | * is in DST or not and therefore adjust the offset appropriately.
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| 87 | *
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| 88 | * The logic is as follows. Starting with UTC time use the offset to
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| 89 | * create a label for an non-dst adjusted local time. Then call
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| 90 | * dst_rules::local_is_dst with the non adjust local time. The
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| 91 | * results of this function will either unabiguously decide that
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| 92 | * the initial local time is in dst or return an illegal or
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| 93 | * ambiguous result. An illegal result only occurs at the end
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| 94 | * of dst (where labels are skipped) and indicates that dst has
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| 95 | * ended. An ambiguous result means that we need to recheck by
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| 96 | * making a dst adjustment and then rechecking. If the dst offset
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| 97 | * is added to the utc time and the recheck proves non-ambiguous
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| 98 | * then we are past the boundary. If it is still ambiguous then
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| 99 | * we are ahead of the boundary and dst is still in effect.
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| 100 | *
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| 101 | * TODO -- check if all dst offsets are positive. If not then
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| 102 | * the algorithm needs to check for this and reverse the
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| 103 | * illegal/ambiguous logic.
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| 104 | */
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| 105 | static time_duration_type utc_to_local_offset(const time_type& t)
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| 106 | {
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| 107 | //get initial local time guess by applying utc offset
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| 108 | time_type initial = t + utc_offset_rules::utc_to_local_base_offset();
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| 109 | time_is_dst_result dst_flag =
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| 110 | dst_rules::local_is_dst(initial.date(), initial.time_of_day());
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| 111 | switch(dst_flag) {
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| 112 | case is_in_dst: return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
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| 113 | case is_not_in_dst: return utc_offset_rules::utc_to_local_base_offset();
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| 114 | case invalid_time_label:return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
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| 115 | case ambiguous: {
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| 116 | time_type retry = initial + dst_rules::dst_offset();
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| 117 | dst_flag = dst_rules::local_is_dst(retry.date(), retry.time_of_day());
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| 118 | //if still ambibuous then the utc time still translates to a dst time
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| 119 | if (dst_flag == ambiguous) {
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| 120 | return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
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| 121 | }
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| 122 | // we are past the dst boundary
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| 123 | else {
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| 124 | return utc_offset_rules::utc_to_local_base_offset();
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| 125 | }
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| 126 | }
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| 127 | }//case
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| 128 | //TODO better excpetion type
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| 129 | throw std::out_of_range("Unreachable case");
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| 130 |
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| 131 | }
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| 132 |
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| 133 | //! Get the offset to UTC given a local time
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| 134 | static time_duration_type local_to_utc_offset(const time_type& t,
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| 135 | date_time::dst_flags dst=date_time::calculate)
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| 136 | {
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| 137 | switch (dst) {
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| 138 | case is_dst:
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| 139 | return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset();
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| 140 | case not_dst:
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| 141 | return utc_offset_rules::local_to_utc_base_offset();
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| 142 | case calculate:
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| 143 | time_is_dst_result res =
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| 144 | dst_rules::local_is_dst(t.date(), t.time_of_day());
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| 145 | switch(res) {
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| 146 | case is_in_dst: return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset();
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| 147 | case is_not_in_dst: return utc_offset_rules::local_to_utc_base_offset();
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| 148 | case ambiguous: return utc_offset_rules::local_to_utc_base_offset();
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| 149 | case invalid_time_label: throw std::out_of_range("Time label invalid");
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| 150 | }
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| 151 | }
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| 152 | throw std::out_of_range("Time label invalid");
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| 153 | }
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| 154 |
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| 155 |
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| 156 | private:
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| 157 |
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| 158 | };
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| 159 |
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| 160 | void dummy_to_prevent_msvc6_ice(); //why ask why?
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| 161 |
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| 162 | //! Template that simplifies the creation of local time calculator
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| 163 | /*! Use this template to create the timezone to utc convertors as required.
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| 164 | *
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| 165 | * This class will also work for other regions that don't use dst and
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| 166 | * have a utc offset which is an integral number of hours.
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| 167 | *
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| 168 | * <b>Template Parameters</b>
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| 169 | * -time_type -- Time class to use
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| 170 | * -utc_offset -- Number hours local time is adjust from utc
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| 171 | * -use_dst -- true (default) if region uses dst, false otherwise
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| 172 | * For example:
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| 173 | * @code
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| 174 | * //eastern timezone is utc-5
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| 175 | typedef date_time::local_adjustor<ptime, -5, us_dst> us_eastern;
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| 176 | typedef date_time::local_adjustor<ptime, -6, us_dst> us_central;
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| 177 | typedef date_time::local_adjustor<ptime, -7, us_dst> us_mountain;
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| 178 | typedef date_time::local_adjustor<ptime, -8, us_dst> us_pacific;
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| 179 | typedef date_time::local_adjustor<ptime, -7, no_dst> us_arizona;
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| 180 | @endcode
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| 181 |
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| 182 | */
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| 183 | template<class time_type, short utc_offset, class dst_rule>
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| 184 | class local_adjustor
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| 185 | {
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| 186 | public:
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| 187 | typedef typename time_type::time_duration_type time_duration_type;
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| 188 | typedef typename time_type::date_type date_type;
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| 189 | typedef static_local_time_adjustor<time_type,
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| 190 | dst_rule,
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| 191 | utc_adjustment<time_duration_type,
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| 192 | utc_offset> > dst_adjustor;
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| 193 | //! Convert a utc time to local time
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| 194 | static time_type utc_to_local(const time_type& t)
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| 195 | {
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| 196 | time_duration_type td = dst_adjustor::utc_to_local_offset(t);
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| 197 | return t + td;
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| 198 | }
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| 199 | //! Convert a local time to utc
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| 200 | static time_type local_to_utc(const time_type& t,
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| 201 | date_time::dst_flags dst=date_time::calculate)
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| 202 | {
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| 203 | time_duration_type td = dst_adjustor::local_to_utc_offset(t, dst);
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| 204 | return t + td;
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| 205 | }
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| 206 | };
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| 207 |
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| 208 |
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| 209 | } } //namespace date_time
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| 210 |
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| 211 |
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| 212 |
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| 213 | #endif
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