| // Copyright 2018 The Abseil Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| // |
| // ----------------------------------------------------------------------------- |
| // File: civil_time.h |
| // ----------------------------------------------------------------------------- |
| // |
| // This header file defines abstractions for computing with "civil time". |
| // The term "civil time" refers to the legally recognized human-scale time |
| // that is represented by the six fields `YYYY-MM-DD hh:mm:ss`. A "date" |
| // is perhaps the most common example of a civil time (represented here as |
| // an `absl::CivilDay`). |
| // |
| // Modern-day civil time follows the Gregorian Calendar and is a |
| // time-zone-independent concept: a civil time of "2015-06-01 12:00:00", for |
| // example, is not tied to a time zone. Put another way, a civil time does not |
| // map to a unique point in time; a civil time must be mapped to an absolute |
| // time *through* a time zone. |
| // |
| // Because a civil time is what most people think of as "time," it is common to |
| // map absolute times to civil times to present to users. |
| // |
| // Time zones define the relationship between absolute and civil times. Given an |
| // absolute or civil time and a time zone, you can compute the other time: |
| // |
| // Civil Time = F(Absolute Time, Time Zone) |
| // Absolute Time = G(Civil Time, Time Zone) |
| // |
| // The Abseil time library allows you to construct such civil times from |
| // absolute times; consult time.h for such functionality. |
| // |
| // This library provides six classes for constructing civil-time objects, and |
| // provides several helper functions for rounding, iterating, and performing |
| // arithmetic on civil-time objects, while avoiding complications like |
| // daylight-saving time (DST): |
| // |
| // * `absl::CivilSecond` |
| // * `absl::CivilMinute` |
| // * `absl::CivilHour` |
| // * `absl::CivilDay` |
| // * `absl::CivilMonth` |
| // * `absl::CivilYear` |
| // |
| // Example: |
| // |
| // // Construct a civil-time object for a specific day |
| // const absl::CivilDay cd(1969, 07, 20); |
| // |
| // // Construct a civil-time object for a specific second |
| // const absl::CivilSecond cd(2018, 8, 1, 12, 0, 1); |
| // |
| // Note: In C++14 and later, this library is usable in a constexpr context. |
| // |
| // Example: |
| // |
| // // Valid in C++14 |
| // constexpr absl::CivilDay cd(1969, 07, 20); |
| |
| #ifndef ABSL_TIME_CIVIL_TIME_H_ |
| #define ABSL_TIME_CIVIL_TIME_H_ |
| |
| #include <string> |
| |
| #include "absl/strings/string_view.h" |
| #include "absl/time/internal/cctz/include/cctz/civil_time.h" |
| |
| namespace absl { |
| inline namespace lts_2019_08_08 { |
| |
| namespace time_internal { |
| struct second_tag : cctz::detail::second_tag {}; |
| struct minute_tag : second_tag, cctz::detail::minute_tag {}; |
| struct hour_tag : minute_tag, cctz::detail::hour_tag {}; |
| struct day_tag : hour_tag, cctz::detail::day_tag {}; |
| struct month_tag : day_tag, cctz::detail::month_tag {}; |
| struct year_tag : month_tag, cctz::detail::year_tag {}; |
| } // namespace time_internal |
| |
| // ----------------------------------------------------------------------------- |
| // CivilSecond, CivilMinute, CivilHour, CivilDay, CivilMonth, CivilYear |
| // ----------------------------------------------------------------------------- |
| // |
| // Each of these civil-time types is a simple value type with the same |
| // interface for construction and the same six accessors for each of the civil |
| // time fields (year, month, day, hour, minute, and second, aka YMDHMS). These |
| // classes differ only in their alignment, which is indicated by the type name |
| // and specifies the field on which arithmetic operates. |
| // |
| // CONSTRUCTION |
| // |
| // Each of the civil-time types can be constructed in two ways: by directly |
| // passing to the constructor up to six integers representing the YMDHMS fields, |
| // or by copying the YMDHMS fields from a differently aligned civil-time type. |
| // Omitted fields are assigned their minimum valid value. Hours, minutes, and |
| // seconds will be set to 0, month and day will be set to 1. Since there is no |
| // minimum year, the default is 1970. |
| // |
| // Examples: |
| // |
| // absl::CivilDay default_value; // 1970-01-01 00:00:00 |
| // |
| // absl::CivilDay a(2015, 2, 3); // 2015-02-03 00:00:00 |
| // absl::CivilDay b(2015, 2, 3, 4, 5, 6); // 2015-02-03 00:00:00 |
| // absl::CivilDay c(2015); // 2015-01-01 00:00:00 |
| // |
| // absl::CivilSecond ss(2015, 2, 3, 4, 5, 6); // 2015-02-03 04:05:06 |
| // absl::CivilMinute mm(ss); // 2015-02-03 04:05:00 |
| // absl::CivilHour hh(mm); // 2015-02-03 04:00:00 |
| // absl::CivilDay d(hh); // 2015-02-03 00:00:00 |
| // absl::CivilMonth m(d); // 2015-02-01 00:00:00 |
| // absl::CivilYear y(m); // 2015-01-01 00:00:00 |
| // |
| // m = absl::CivilMonth(y); // 2015-01-01 00:00:00 |
| // d = absl::CivilDay(m); // 2015-01-01 00:00:00 |
| // hh = absl::CivilHour(d); // 2015-01-01 00:00:00 |
| // mm = absl::CivilMinute(hh); // 2015-01-01 00:00:00 |
| // ss = absl::CivilSecond(mm); // 2015-01-01 00:00:00 |
| // |
| // Each civil-time class is aligned to the civil-time field indicated in the |
| // class's name after normalization. Alignment is performed by setting all the |
| // inferior fields to their minimum valid value (as described above). The |
| // following are examples of how each of the six types would align the fields |
| // representing November 22, 2015 at 12:34:56 in the afternoon. (Note: the |
| // string format used here is not important; it's just a shorthand way of |
| // showing the six YMDHMS fields.) |
| // |
| // absl::CivilSecond : 2015-11-22 12:34:56 |
| // absl::CivilMinute : 2015-11-22 12:34:00 |
| // absl::CivilHour : 2015-11-22 12:00:00 |
| // absl::CivilDay : 2015-11-22 00:00:00 |
| // absl::CivilMonth : 2015-11-01 00:00:00 |
| // absl::CivilYear : 2015-01-01 00:00:00 |
| // |
| // Each civil-time type performs arithmetic on the field to which it is |
| // aligned. This means that adding 1 to an absl::CivilDay increments the day |
| // field (normalizing as necessary), and subtracting 7 from an absl::CivilMonth |
| // operates on the month field (normalizing as necessary). All arithmetic |
| // produces a valid civil time. Difference requires two similarly aligned |
| // civil-time objects and returns the scalar answer in units of the objects' |
| // alignment. For example, the difference between two absl::CivilHour objects |
| // will give an answer in units of civil hours. |
| // |
| // ALIGNMENT CONVERSION |
| // |
| // The alignment of a civil-time object cannot change, but the object may be |
| // used to construct a new object with a different alignment. This is referred |
| // to as "realigning". When realigning to a type with the same or more |
| // precision (e.g., absl::CivilDay -> absl::CivilSecond), the conversion may be |
| // performed implicitly since no information is lost. However, if information |
| // could be discarded (e.g., CivilSecond -> CivilDay), the conversion must |
| // be explicit at the call site. |
| // |
| // Examples: |
| // |
| // void UseDay(absl::CivilDay day); |
| // |
| // absl::CivilSecond cs; |
| // UseDay(cs); // Won't compile because data may be discarded |
| // UseDay(absl::CivilDay(cs)); // OK: explicit conversion |
| // |
| // absl::CivilDay cd; |
| // UseDay(cd); // OK: no conversion needed |
| // |
| // absl::CivilMonth cm; |
| // UseDay(cm); // OK: implicit conversion to absl::CivilDay |
| // |
| // NORMALIZATION |
| // |
| // Normalization takes invalid values and adjusts them to produce valid values. |
| // Within the civil-time library, integer arguments passed to the Civil* |
| // constructors may be out-of-range, in which case they are normalized by |
| // carrying overflow into a field of courser granularity to produce valid |
| // civil-time objects. This normalization enables natural arithmetic on |
| // constructor arguments without worrying about the field's range. |
| // |
| // Examples: |
| // |
| // // Out-of-range; normalized to 2016-11-01 |
| // absl::CivilDay d(2016, 10, 32); |
| // // Out-of-range, negative: normalized to 2016-10-30T23 |
| // absl::CivilHour h1(2016, 10, 31, -1); |
| // // Normalization is cumulative: normalized to 2016-10-30T23 |
| // absl::CivilHour h2(2016, 10, 32, -25); |
| // |
| // Note: If normalization is undesired, you can signal an error by comparing |
| // the constructor arguments to the normalized values returned by the YMDHMS |
| // properties. |
| // |
| // COMPARISON |
| // |
| // Comparison between civil-time objects considers all six YMDHMS fields, |
| // regardless of the type's alignment. Comparison between differently aligned |
| // civil-time types is allowed. |
| // |
| // Examples: |
| // |
| // absl::CivilDay feb_3(2015, 2, 3); // 2015-02-03 00:00:00 |
| // absl::CivilDay mar_4(2015, 3, 4); // 2015-03-04 00:00:00 |
| // // feb_3 < mar_4 |
| // // absl::CivilYear(feb_3) == absl::CivilYear(mar_4) |
| // |
| // absl::CivilSecond feb_3_noon(2015, 2, 3, 12, 0, 0); // 2015-02-03 12:00:00 |
| // // feb_3 < feb_3_noon |
| // // feb_3 == absl::CivilDay(feb_3_noon) |
| // |
| // // Iterates all the days of February 2015. |
| // for (absl::CivilDay d(2015, 2, 1); d < absl::CivilMonth(2015, 3); ++d) { |
| // // ... |
| // } |
| // |
| // ARITHMETIC |
| // |
| // Civil-time types support natural arithmetic operators such as addition, |
| // subtraction, and difference. Arithmetic operates on the civil-time field |
| // indicated in the type's name. Difference operators require arguments with |
| // the same alignment and return the answer in units of the alignment. |
| // |
| // Example: |
| // |
| // absl::CivilDay a(2015, 2, 3); |
| // ++a; // 2015-02-04 00:00:00 |
| // --a; // 2015-02-03 00:00:00 |
| // absl::CivilDay b = a + 1; // 2015-02-04 00:00:00 |
| // absl::CivilDay c = 1 + b; // 2015-02-05 00:00:00 |
| // int n = c - a; // n = 2 (civil days) |
| // int m = c - absl::CivilMonth(c); // Won't compile: different types. |
| // |
| // ACCESSORS |
| // |
| // Each civil-time type has accessors for all six of the civil-time fields: |
| // year, month, day, hour, minute, and second. |
| // |
| // civil_year_t year() |
| // int month() |
| // int day() |
| // int hour() |
| // int minute() |
| // int second() |
| // |
| // Recall that fields inferior to the type's aligment will be set to their |
| // minimum valid value. |
| // |
| // Example: |
| // |
| // absl::CivilDay d(2015, 6, 28); |
| // // d.year() == 2015 |
| // // d.month() == 6 |
| // // d.day() == 28 |
| // // d.hour() == 0 |
| // // d.minute() == 0 |
| // // d.second() == 0 |
| // |
| // CASE STUDY: Adding a month to January 31. |
| // |
| // One of the classic questions that arises when considering a civil time |
| // library (or a date library or a date/time library) is this: |
| // "What is the result of adding a month to January 31?" |
| // This is an interesting question because it is unclear what is meant by a |
| // "month", and several different answers are possible, depending on context: |
| // |
| // 1. March 3 (or 2 if a leap year), if "add a month" means to add a month to |
| // the current month, and adjust the date to overflow the extra days into |
| // March. In this case the result of "February 31" would be normalized as |
| // within the civil-time library. |
| // 2. February 28 (or 29 if a leap year), if "add a month" means to add a |
| // month, and adjust the date while holding the resulting month constant. |
| // In this case, the result of "February 31" would be truncated to the last |
| // day in February. |
| // 3. An error. The caller may get some error, an exception, an invalid date |
| // object, or perhaps return `false`. This may make sense because there is |
| // no single unambiguously correct answer to the question. |
| // |
| // Practically speaking, any answer that is not what the programmer intended |
| // is the wrong answer. |
| // |
| // The Abseil time library avoids this problem by making it impossible to |
| // ask ambiguous questions. All civil-time objects are aligned to a particular |
| // civil-field boundary (such as aligned to a year, month, day, hour, minute, |
| // or second), and arithmetic operates on the field to which the object is |
| // aligned. This means that in order to "add a month" the object must first be |
| // aligned to a month boundary, which is equivalent to the first day of that |
| // month. |
| // |
| // Of course, there are ways to compute an answer the question at hand using |
| // this Abseil time library, but they require the programmer to be explicit |
| // about the answer they expect. To illustrate, let's see how to compute all |
| // three of the above possible answers to the question of "Jan 31 plus 1 |
| // month": |
| // |
| // Example: |
| // |
| // const absl::CivilDay d(2015, 1, 31); |
| // |
| // // Answer 1: |
| // // Add 1 to the month field in the constructor, and rely on normalization. |
| // const auto normalized = absl::CivilDay(d.year(), d.month() + 1, d.day()); |
| // // normalized == 2015-03-03 (aka Feb 31) |
| // |
| // // Answer 2: |
| // // Add 1 to month field, capping to the end of next month. |
| // const auto next_month = absl::CivilMonth(d) + 1; |
| // const auto last_day_of_next_month = absl::CivilDay(next_month + 1) - 1; |
| // const auto capped = std::min(normalized, last_day_of_next_month); |
| // // capped == 2015-02-28 |
| // |
| // // Answer 3: |
| // // Signal an error if the normalized answer is not in next month. |
| // if (absl::CivilMonth(normalized) != next_month) { |
| // // error, month overflow |
| // } |
| // |
| using CivilSecond = |
| time_internal::cctz::detail::civil_time<time_internal::second_tag>; |
| using CivilMinute = |
| time_internal::cctz::detail::civil_time<time_internal::minute_tag>; |
| using CivilHour = |
| time_internal::cctz::detail::civil_time<time_internal::hour_tag>; |
| using CivilDay = |
| time_internal::cctz::detail::civil_time<time_internal::day_tag>; |
| using CivilMonth = |
| time_internal::cctz::detail::civil_time<time_internal::month_tag>; |
| using CivilYear = |
| time_internal::cctz::detail::civil_time<time_internal::year_tag>; |
| |
| // civil_year_t |
| // |
| // Type alias of a civil-time year value. This type is guaranteed to (at least) |
| // support any year value supported by `time_t`. |
| // |
| // Example: |
| // |
| // absl::CivilSecond cs = ...; |
| // absl::civil_year_t y = cs.year(); |
| // cs = absl::CivilSecond(y, 1, 1, 0, 0, 0); // CivilSecond(CivilYear(cs)) |
| // |
| using civil_year_t = time_internal::cctz::year_t; |
| |
| // civil_diff_t |
| // |
| // Type alias of the difference between two civil-time values. |
| // This type is used to indicate arguments that are not |
| // normalized (such as parameters to the civil-time constructors), the results |
| // of civil-time subtraction, or the operand to civil-time addition. |
| // |
| // Example: |
| // |
| // absl::civil_diff_t n_sec = cs1 - cs2; // cs1 == cs2 + n_sec; |
| // |
| using civil_diff_t = time_internal::cctz::diff_t; |
| |
| // Weekday::monday, Weekday::tuesday, Weekday::wednesday, Weekday::thursday, |
| // Weekday::friday, Weekday::saturday, Weekday::sunday |
| // |
| // The Weekday enum class represents the civil-time concept of a "weekday" with |
| // members for all days of the week. |
| // |
| // absl::Weekday wd = absl::Weekday::thursday; |
| // |
| using Weekday = time_internal::cctz::weekday; |
| |
| // GetWeekday() |
| // |
| // Returns the absl::Weekday for the given (realigned) civil-time value. |
| // |
| // Example: |
| // |
| // absl::CivilDay a(2015, 8, 13); |
| // absl::Weekday wd = absl::GetWeekday(a); // wd == absl::Weekday::thursday |
| // |
| inline Weekday GetWeekday(CivilSecond cs) { |
| return time_internal::cctz::get_weekday(cs); |
| } |
| |
| // NextWeekday() |
| // PrevWeekday() |
| // |
| // Returns the absl::CivilDay that strictly follows or precedes a given |
| // absl::CivilDay, and that falls on the given absl::Weekday. |
| // |
| // Example, given the following month: |
| // |
| // August 2015 |
| // Su Mo Tu We Th Fr Sa |
| // 1 |
| // 2 3 4 5 6 7 8 |
| // 9 10 11 12 13 14 15 |
| // 16 17 18 19 20 21 22 |
| // 23 24 25 26 27 28 29 |
| // 30 31 |
| // |
| // absl::CivilDay a(2015, 8, 13); |
| // // absl::GetWeekday(a) == absl::Weekday::thursday |
| // absl::CivilDay b = absl::NextWeekday(a, absl::Weekday::thursday); |
| // // b = 2015-08-20 |
| // absl::CivilDay c = absl::PrevWeekday(a, absl::Weekday::thursday); |
| // // c = 2015-08-06 |
| // |
| // absl::CivilDay d = ... |
| // // Gets the following Thursday if d is not already Thursday |
| // absl::CivilDay thurs1 = absl::NextWeekday(d - 1, absl::Weekday::thursday); |
| // // Gets the previous Thursday if d is not already Thursday |
| // absl::CivilDay thurs2 = absl::PrevWeekday(d + 1, absl::Weekday::thursday); |
| // |
| inline CivilDay NextWeekday(CivilDay cd, Weekday wd) { |
| return CivilDay(time_internal::cctz::next_weekday(cd, wd)); |
| } |
| inline CivilDay PrevWeekday(CivilDay cd, Weekday wd) { |
| return CivilDay(time_internal::cctz::prev_weekday(cd, wd)); |
| } |
| |
| // GetYearDay() |
| // |
| // Returns the day-of-year for the given (realigned) civil-time value. |
| // |
| // Example: |
| // |
| // absl::CivilDay a(2015, 1, 1); |
| // int yd_jan_1 = absl::GetYearDay(a); // yd_jan_1 = 1 |
| // absl::CivilDay b(2015, 12, 31); |
| // int yd_dec_31 = absl::GetYearDay(b); // yd_dec_31 = 365 |
| // |
| inline int GetYearDay(CivilSecond cs) { |
| return time_internal::cctz::get_yearday(cs); |
| } |
| |
| // FormatCivilTime() |
| // |
| // Formats the given civil-time value into a string value of the following |
| // format: |
| // |
| // Type | Format |
| // --------------------------------- |
| // CivilSecond | YYYY-MM-DDTHH:MM:SS |
| // CivilMinute | YYYY-MM-DDTHH:MM |
| // CivilHour | YYYY-MM-DDTHH |
| // CivilDay | YYYY-MM-DD |
| // CivilMonth | YYYY-MM |
| // CivilYear | YYYY |
| // |
| // Example: |
| // |
| // absl::CivilDay d = absl::CivilDay(1969, 7, 20); |
| // std::string day_string = absl::FormatCivilTime(d); // "1969-07-20" |
| // |
| std::string FormatCivilTime(CivilSecond c); |
| std::string FormatCivilTime(CivilMinute c); |
| std::string FormatCivilTime(CivilHour c); |
| std::string FormatCivilTime(CivilDay c); |
| std::string FormatCivilTime(CivilMonth c); |
| std::string FormatCivilTime(CivilYear c); |
| |
| namespace time_internal { // For functions found via ADL on civil-time tags. |
| |
| // Streaming Operators |
| // |
| // Each civil-time type may be sent to an output stream using operator<<(). |
| // The result matches the string produced by `FormatCivilTime()`. |
| // |
| // Example: |
| // |
| // absl::CivilDay d = absl::CivilDay("1969-07-20"); |
| // std::cout << "Date is: " << d << "\n"; |
| // |
| std::ostream& operator<<(std::ostream& os, CivilYear y); |
| std::ostream& operator<<(std::ostream& os, CivilMonth m); |
| std::ostream& operator<<(std::ostream& os, CivilDay d); |
| std::ostream& operator<<(std::ostream& os, CivilHour h); |
| std::ostream& operator<<(std::ostream& os, CivilMinute m); |
| std::ostream& operator<<(std::ostream& os, CivilSecond s); |
| |
| } // namespace time_internal |
| |
| } // inline namespace lts_2019_08_08 |
| } // namespace absl |
| |
| #endif // ABSL_TIME_CIVIL_TIME_H_ |
