Abseil Common Libraries (C++) (grcp 依赖)
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485 lines
18 KiB
485 lines
18 KiB
// Copyright 2018 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// |
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// ----------------------------------------------------------------------------- |
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// File: civil_time.h |
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// ----------------------------------------------------------------------------- |
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// |
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// This header file defines abstractions for computing with "civil time". |
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// The term "civil time" refers to the legally recognized human-scale time |
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// that is represented by the six fields `YYYY-MM-DD hh:mm:ss`. A "date" |
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// is perhaps the most common example of a civil time (represented here as |
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// an `absl::CivilDay`). |
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// |
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// Modern-day civil time follows the Gregorian Calendar and is a |
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// time-zone-independent concept: a civil time of "2015-06-01 12:00:00", for |
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// example, is not tied to a time zone. Put another way, a civil time does not |
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// map to a unique point in time; a civil time must be mapped to an absolute |
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// time *through* a time zone. |
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// |
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// Because a civil time is what most people think of as "time," it is common to |
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// map absolute times to civil times to present to users. |
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// |
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// Time zones define the relationship between absolute and civil times. Given an |
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// absolute or civil time and a time zone, you can compute the other time: |
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// |
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// Civil Time = F(Absolute Time, Time Zone) |
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// Absolute Time = G(Civil Time, Time Zone) |
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// |
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// The Abseil time library allows you to construct such civil times from |
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// absolute times; consult time.h for such functionality. |
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// |
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// This library provides six classes for constructing civil-time objects, and |
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// provides several helper functions for rounding, iterating, and performing |
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// arithmetic on civil-time objects, while avoiding complications like |
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// daylight-saving time (DST): |
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// |
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// * `absl::CivilSecond` |
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// * `absl::CivilMinute` |
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// * `absl::CivilHour` |
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// * `absl::CivilDay` |
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// * `absl::CivilMonth` |
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// * `absl::CivilYear` |
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// |
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// Example: |
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// |
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// // Construct a civil-time object for a specific day |
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// const absl::CivilDay cd(1969, 07, 20); |
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// |
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// // Construct a civil-time object for a specific second |
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// const absl::CivilSecond cd(2018, 8, 1, 12, 0, 1); |
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// |
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// Note: In C++14 and later, this library is usable in a constexpr context. |
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// |
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// Example: |
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// |
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// // Valid in C++14 |
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// constexpr absl::CivilDay cd(1969, 07, 20); |
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#ifndef ABSL_TIME_CIVIL_TIME_H_ |
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#define ABSL_TIME_CIVIL_TIME_H_ |
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#include <string> |
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#include "absl/strings/string_view.h" |
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#include "absl/time/internal/cctz/include/cctz/civil_time.h" |
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namespace absl { |
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namespace time_internal { |
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struct second_tag : cctz::detail::second_tag {}; |
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struct minute_tag : second_tag, cctz::detail::minute_tag {}; |
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struct hour_tag : minute_tag, cctz::detail::hour_tag {}; |
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struct day_tag : hour_tag, cctz::detail::day_tag {}; |
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struct month_tag : day_tag, cctz::detail::month_tag {}; |
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struct year_tag : month_tag, cctz::detail::year_tag {}; |
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} // namespace time_internal |
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// ----------------------------------------------------------------------------- |
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// CivilSecond, CivilMinute, CivilHour, CivilDay, CivilMonth, CivilYear |
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// ----------------------------------------------------------------------------- |
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// |
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// Each of these civil-time types is a simple value type with the same |
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// interface for construction and the same six accessors for each of the civil |
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// time fields (year, month, day, hour, minute, and second, aka YMDHMS). These |
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// classes differ only in their alignment, which is indicated by the type name |
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// and specifies the field on which arithmetic operates. |
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// |
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// CONSTRUCTION |
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// |
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// Each of the civil-time types can be constructed in two ways: by directly |
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// passing to the constructor up to six integers representing the YMDHMS fields, |
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// or by copying the YMDHMS fields from a differently aligned civil-time type. |
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// Omitted fields are assigned their minimum valid value. Hours, minutes, and |
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// seconds will be set to 0, month and day will be set to 1. Since there is no |
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// minimum year, the default is 1970. |
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// |
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// Examples: |
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// |
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// absl::CivilDay default_value; // 1970-01-01 00:00:00 |
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// |
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// absl::CivilDay a(2015, 2, 3); // 2015-02-03 00:00:00 |
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// absl::CivilDay b(2015, 2, 3, 4, 5, 6); // 2015-02-03 00:00:00 |
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// absl::CivilDay c(2015); // 2015-01-01 00:00:00 |
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// |
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// absl::CivilSecond ss(2015, 2, 3, 4, 5, 6); // 2015-02-03 04:05:06 |
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// absl::CivilMinute mm(ss); // 2015-02-03 04:05:00 |
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// absl::CivilHour hh(mm); // 2015-02-03 04:00:00 |
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// absl::CivilDay d(hh); // 2015-02-03 00:00:00 |
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// absl::CivilMonth m(d); // 2015-02-01 00:00:00 |
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// absl::CivilYear y(m); // 2015-01-01 00:00:00 |
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// |
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// m = absl::CivilMonth(y); // 2015-01-01 00:00:00 |
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// d = absl::CivilDay(m); // 2015-01-01 00:00:00 |
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// hh = absl::CivilHour(d); // 2015-01-01 00:00:00 |
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// mm = absl::CivilMinute(hh); // 2015-01-01 00:00:00 |
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// ss = absl::CivilSecond(mm); // 2015-01-01 00:00:00 |
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// |
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// Each civil-time class is aligned to the civil-time field indicated in the |
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// class's name after normalization. Alignment is performed by setting all the |
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// inferior fields to their minimum valid value (as described above). The |
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// following are examples of how each of the six types would align the fields |
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// representing November 22, 2015 at 12:34:56 in the afternoon. (Note: the |
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// string format used here is not important; it's just a shorthand way of |
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// showing the six YMDHMS fields.) |
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// |
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// absl::CivilSecond : 2015-11-22 12:34:56 |
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// absl::CivilMinute : 2015-11-22 12:34:00 |
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// absl::CivilHour : 2015-11-22 12:00:00 |
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// absl::CivilDay : 2015-11-22 00:00:00 |
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// absl::CivilMonth : 2015-11-01 00:00:00 |
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// absl::CivilYear : 2015-01-01 00:00:00 |
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// |
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// Each civil-time type performs arithmetic on the field to which it is |
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// aligned. This means that adding 1 to an absl::CivilDay increments the day |
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// field (normalizing as necessary), and subtracting 7 from an absl::CivilMonth |
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// operates on the month field (normalizing as necessary). All arithmetic |
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// produces a valid civil time. Difference requires two similarly aligned |
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// civil-time objects and returns the scalar answer in units of the objects' |
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// alignment. For example, the difference between two absl::CivilHour objects |
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// will give an answer in units of civil hours. |
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// |
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// ALIGNMENT CONVERSION |
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// |
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// The alignment of a civil-time object cannot change, but the object may be |
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// used to construct a new object with a different alignment. This is referred |
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// to as "realigning". When realigning to a type with the same or more |
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// precision (e.g., absl::CivilDay -> absl::CivilSecond), the conversion may be |
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// performed implicitly since no information is lost. However, if information |
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// could be discarded (e.g., CivilSecond -> CivilDay), the conversion must |
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// be explicit at the call site. |
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// |
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// Examples: |
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// |
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// void UseDay(absl::CivilDay day); |
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// |
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// absl::CivilSecond cs; |
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// UseDay(cs); // Won't compile because data may be discarded |
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// UseDay(absl::CivilDay(cs)); // OK: explicit conversion |
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// |
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// absl::CivilDay cd; |
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// UseDay(cd); // OK: no conversion needed |
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// |
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// absl::CivilMonth cm; |
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// UseDay(cm); // OK: implicit conversion to absl::CivilDay |
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// |
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// NORMALIZATION |
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// |
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// Normalization takes invalid values and adjusts them to produce valid values. |
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// Within the civil-time library, integer arguments passed to the Civil* |
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// constructors may be out-of-range, in which case they are normalized by |
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// carrying overflow into a field of courser granularity to produce valid |
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// civil-time objects. This normalization enables natural arithmetic on |
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// constructor arguments without worrying about the field's range. |
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// |
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// Examples: |
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// |
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// // Out-of-range; normalized to 2016-11-01 |
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// absl::CivilDay d(2016, 10, 32); |
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// // Out-of-range, negative: normalized to 2016-10-30T23 |
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// absl::CivilHour h1(2016, 10, 31, -1); |
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// // Normalization is cumulative: normalized to 2016-10-30T23 |
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// absl::CivilHour h2(2016, 10, 32, -25); |
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// |
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// Note: If normalization is undesired, you can signal an error by comparing |
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// the constructor arguments to the normalized values returned by the YMDHMS |
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// properties. |
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// |
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// COMPARISON |
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// |
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// Comparison between civil-time objects considers all six YMDHMS fields, |
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// regardless of the type's alignment. Comparison between differently aligned |
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// civil-time types is allowed. |
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// |
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// Examples: |
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// |
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// absl::CivilDay feb_3(2015, 2, 3); // 2015-02-03 00:00:00 |
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// absl::CivilDay mar_4(2015, 3, 4); // 2015-03-04 00:00:00 |
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// // feb_3 < mar_4 |
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// // absl::CivilYear(feb_3) == absl::CivilYear(mar_4) |
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// |
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// absl::CivilSecond feb_3_noon(2015, 2, 3, 12, 0, 0); // 2015-02-03 12:00:00 |
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// // feb_3 < feb_3_noon |
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// // feb_3 == absl::CivilDay(feb_3_noon) |
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// |
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// // Iterates all the days of February 2015. |
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// for (absl::CivilDay d(2015, 2, 1); d < absl::CivilMonth(2015, 3); ++d) { |
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// // ... |
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// } |
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// |
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// ARITHMETIC |
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// |
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// Civil-time types support natural arithmetic operators such as addition, |
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// subtraction, and difference. Arithmetic operates on the civil-time field |
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// indicated in the type's name. Difference operators require arguments with |
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// the same alignment and return the answer in units of the alignment. |
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// |
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// Example: |
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// |
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// absl::CivilDay a(2015, 2, 3); |
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// ++a; // 2015-02-04 00:00:00 |
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// --a; // 2015-02-03 00:00:00 |
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// absl::CivilDay b = a + 1; // 2015-02-04 00:00:00 |
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// absl::CivilDay c = 1 + b; // 2015-02-05 00:00:00 |
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// int n = c - a; // n = 2 (civil days) |
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// int m = c - absl::CivilMonth(c); // Won't compile: different types. |
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// |
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// ACCESSORS |
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// |
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// Each civil-time type has accessors for all six of the civil-time fields: |
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// year, month, day, hour, minute, and second. |
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// |
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// civil_year_t year() |
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// int month() |
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// int day() |
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// int hour() |
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// int minute() |
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// int second() |
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// |
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// Recall that fields inferior to the type's aligment will be set to their |
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// minimum valid value. |
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// |
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// Example: |
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// |
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// absl::CivilDay d(2015, 6, 28); |
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// // d.year() == 2015 |
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// // d.month() == 6 |
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// // d.day() == 28 |
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// // d.hour() == 0 |
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// // d.minute() == 0 |
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// // d.second() == 0 |
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// |
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// CASE STUDY: Adding a month to January 31. |
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// |
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// One of the classic questions that arises when considering a civil time |
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// library (or a date library or a date/time library) is this: |
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// "What is the result of adding a month to January 31?" |
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// This is an interesting question because it is unclear what is meant by a |
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// "month", and several different answers are possible, depending on context: |
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// |
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// 1. March 3 (or 2 if a leap year), if "add a month" means to add a month to |
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// the current month, and adjust the date to overflow the extra days into |
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// March. In this case the result of "February 31" would be normalized as |
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// within the civil-time library. |
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// 2. February 28 (or 29 if a leap year), if "add a month" means to add a |
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// month, and adjust the date while holding the resulting month constant. |
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// In this case, the result of "February 31" would be truncated to the last |
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// day in February. |
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// 3. An error. The caller may get some error, an exception, an invalid date |
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// object, or perhaps return `false`. This may make sense because there is |
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// no single unambiguously correct answer to the question. |
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// |
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// Practically speaking, any answer that is not what the programmer intended |
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// is the wrong answer. |
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// |
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// The Abseil time library avoids this problem by making it impossible to |
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// ask ambiguous questions. All civil-time objects are aligned to a particular |
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// civil-field boundary (such as aligned to a year, month, day, hour, minute, |
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// or second), and arithmetic operates on the field to which the object is |
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// aligned. This means that in order to "add a month" the object must first be |
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// aligned to a month boundary, which is equivalent to the first day of that |
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// month. |
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// |
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// Of course, there are ways to compute an answer the question at hand using |
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// this Abseil time library, but they require the programmer to be explicit |
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// about the answer they expect. To illustrate, let's see how to compute all |
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// three of the above possible answers to the question of "Jan 31 plus 1 |
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// month": |
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// |
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// Example: |
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// |
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// const absl::CivilDay d(2015, 1, 31); |
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// |
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// // Answer 1: |
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// // Add 1 to the month field in the constructor, and rely on normalization. |
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// const auto normalized = absl::CivilDay(d.year(), d.month() + 1, d.day()); |
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// // normalized == 2015-03-03 (aka Feb 31) |
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// |
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// // Answer 2: |
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// // Add 1 to month field, capping to the end of next month. |
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// const auto next_month = absl::CivilMonth(d) + 1; |
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// const auto last_day_of_next_month = absl::CivilDay(next_month + 1) - 1; |
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// const auto capped = std::min(normalized, last_day_of_next_month); |
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// // capped == 2015-02-28 |
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// |
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// // Answer 3: |
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// // Signal an error if the normalized answer is not in next month. |
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// if (absl::CivilMonth(normalized) != next_month) { |
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// // error, month overflow |
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// } |
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// |
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using CivilSecond = |
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time_internal::cctz::detail::civil_time<time_internal::second_tag>; |
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using CivilMinute = |
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time_internal::cctz::detail::civil_time<time_internal::minute_tag>; |
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using CivilHour = |
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time_internal::cctz::detail::civil_time<time_internal::hour_tag>; |
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using CivilDay = |
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time_internal::cctz::detail::civil_time<time_internal::day_tag>; |
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using CivilMonth = |
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time_internal::cctz::detail::civil_time<time_internal::month_tag>; |
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using CivilYear = |
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time_internal::cctz::detail::civil_time<time_internal::year_tag>; |
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// civil_year_t |
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// |
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// Type alias of a civil-time year value. This type is guaranteed to (at least) |
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// support any year value supported by `time_t`. |
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// |
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// Example: |
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// |
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// absl::CivilSecond cs = ...; |
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// absl::civil_year_t y = cs.year(); |
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// cs = absl::CivilSecond(y, 1, 1, 0, 0, 0); // CivilSecond(CivilYear(cs)) |
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// |
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using civil_year_t = time_internal::cctz::year_t; |
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// civil_diff_t |
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// |
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// Type alias of the difference between two civil-time values. |
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// This type is used to indicate arguments that are not |
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// normalized (such as parameters to the civil-time constructors), the results |
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// of civil-time subtraction, or the operand to civil-time addition. |
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// |
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// Example: |
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// |
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// absl::civil_diff_t n_sec = cs1 - cs2; // cs1 == cs2 + n_sec; |
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// |
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using civil_diff_t = time_internal::cctz::diff_t; |
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// Weekday::monday, Weekday::tuesday, Weekday::wednesday, Weekday::thursday, |
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// Weekday::friday, Weekday::saturday, Weekday::sunday |
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// |
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// The Weekday enum class represents the civil-time concept of a "weekday" with |
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// members for all days of the week. |
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// |
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// absl::Weekday wd = absl::Weekday::thursday; |
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// |
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using Weekday = time_internal::cctz::weekday; |
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// GetWeekday() |
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// |
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// Returns the absl::Weekday for the given absl::CivilDay. |
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// |
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// Example: |
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// |
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// absl::CivilDay a(2015, 8, 13); |
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// absl::Weekday wd = absl::GetWeekday(a); // wd == absl::Weekday::thursday |
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// |
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inline Weekday GetWeekday(CivilDay cd) { |
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return time_internal::cctz::get_weekday(cd); |
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} |
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// NextWeekday() |
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// PrevWeekday() |
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// |
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// Returns the absl::CivilDay that strictly follows or precedes a given |
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// absl::CivilDay, and that falls on the given absl::Weekday. |
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// |
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// Example, given the following month: |
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// |
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// August 2015 |
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// Su Mo Tu We Th Fr Sa |
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// 1 |
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// 2 3 4 5 6 7 8 |
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// 9 10 11 12 13 14 15 |
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// 16 17 18 19 20 21 22 |
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// 23 24 25 26 27 28 29 |
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// 30 31 |
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// |
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// absl::CivilDay a(2015, 8, 13); |
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// // absl::GetWeekday(a) == absl::Weekday::thursday |
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// absl::CivilDay b = absl::NextWeekday(a, absl::Weekday::thursday); |
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// // b = 2015-08-20 |
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// absl::CivilDay c = absl::PrevWeekday(a, absl::Weekday::thursday); |
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// // c = 2015-08-06 |
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// |
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// absl::CivilDay d = ... |
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// // Gets the following Thursday if d is not already Thursday |
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// absl::CivilDay thurs1 = absl::NextWeekday(d - 1, absl::Weekday::thursday); |
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// // Gets the previous Thursday if d is not already Thursday |
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// absl::CivilDay thurs2 = absl::PrevWeekday(d + 1, absl::Weekday::thursday); |
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// |
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inline CivilDay NextWeekday(CivilDay cd, Weekday wd) { |
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return CivilDay(time_internal::cctz::next_weekday(cd, wd)); |
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} |
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inline CivilDay PrevWeekday(CivilDay cd, Weekday wd) { |
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return CivilDay(time_internal::cctz::prev_weekday(cd, wd)); |
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} |
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// GetYearDay() |
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// |
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// Returns the day-of-year for the given absl::CivilDay. |
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// |
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// Example: |
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// |
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// absl::CivilDay a(2015, 1, 1); |
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// int yd_jan_1 = absl::GetYearDay(a); // yd_jan_1 = 1 |
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// absl::CivilDay b(2015, 12, 31); |
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// int yd_dec_31 = absl::GetYearDay(b); // yd_dec_31 = 365 |
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// |
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inline int GetYearDay(CivilDay cd) { |
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return time_internal::cctz::get_yearday(cd); |
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} |
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// FormatCivilTime() |
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// |
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// Formats the given civil-time value into a string value of the following |
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// format: |
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// |
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// Type | Format |
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// --------------------------------- |
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// CivilSecond | YYYY-MM-DDTHH:MM:SS |
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// CivilMinute | YYYY-MM-DDTHH:MM |
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// CivilHour | YYYY-MM-DDTHH |
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// CivilDay | YYYY-MM-DD |
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// CivilMonth | YYYY-MM |
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// CivilYear | YYYY |
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// |
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// Example: |
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// |
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// absl::CivilDay d = absl::CivilDay(1969, 7, 20); |
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// std::string day_string = absl::FormatCivilTime(d); // "1969-07-20" |
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// |
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std::string FormatCivilTime(CivilSecond c); |
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std::string FormatCivilTime(CivilMinute c); |
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std::string FormatCivilTime(CivilHour c); |
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std::string FormatCivilTime(CivilDay c); |
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std::string FormatCivilTime(CivilMonth c); |
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std::string FormatCivilTime(CivilYear c); |
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namespace time_internal { // For functions found via ADL on civil-time tags. |
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// Streaming Operators |
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// |
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// Each civil-time type may be sent to an output stream using operator<<(). |
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// The result matches the string produced by `FormatCivilTime()`. |
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// |
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// Example: |
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// |
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// absl::CivilDay d = absl::CivilDay("1969-07-20"); |
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// std::cout << "Date is: " << d << "\n"; |
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// |
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std::ostream& operator<<(std::ostream& os, CivilYear y); |
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std::ostream& operator<<(std::ostream& os, CivilMonth m); |
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std::ostream& operator<<(std::ostream& os, CivilDay d); |
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std::ostream& operator<<(std::ostream& os, CivilHour h); |
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std::ostream& operator<<(std::ostream& os, CivilMinute m); |
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std::ostream& operator<<(std::ostream& os, CivilSecond s); |
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} // namespace time_internal |
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} // namespace absl |
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#endif // ABSL_TIME_CIVIL_TIME_H_
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