diff options
Diffstat (limited to 'absl/time/internal/cctz/include/cctz/time_zone.h')
| -rw-r--r-- | absl/time/internal/cctz/include/cctz/time_zone.h | 77 |
1 files changed, 70 insertions, 7 deletions
diff --git a/absl/time/internal/cctz/include/cctz/time_zone.h b/absl/time/internal/cctz/include/cctz/time_zone.h index 55804ba6..0b9764ea 100644 --- a/absl/time/internal/cctz/include/cctz/time_zone.h +++ b/absl/time/internal/cctz/include/cctz/time_zone.h @@ -119,7 +119,7 @@ class time_zone { // of the given civil-time argument, and the pre, trans, and post // members will give the absolute time answers using the pre-transition // offset, the transition point itself, and the post-transition offset, - // respectively (all three times are equal if kind == UNIQUE). If any + // respectively (all three times are equal if kind == UNIQUE). If any // of these three absolute times is outside the representable range of a // time_point<seconds> the field is set to its maximum/minimum value. // @@ -159,17 +159,79 @@ class time_zone { }; civil_lookup lookup(const civil_second& cs) const; + // Finds the time of the next/previous offset change in this time zone. + // + // By definition, next_transition(tp, &trans) returns false when tp has + // its maximum value, and prev_transition(tp, &trans) returns false + // when tp has its minimum value. If the zone has no transitions, the + // result will also be false no matter what the argument. + // + // Otherwise, when tp has its minimum value, next_transition(tp, &trans) + // returns true and sets trans to the first recorded transition. Chains + // of calls to next_transition()/prev_transition() will eventually return + // false, but it is unspecified exactly when next_transition(tp, &trans) + // jumps to false, or what time is set by prev_transition(tp, &trans) for + // a very distant tp. + // + // Note: Enumeration of time-zone transitions is for informational purposes + // only. Modern time-related code should not care about when offset changes + // occur. + // + // Example: + // cctz::time_zone nyc; + // if (!cctz::load_time_zone("America/New_York", &nyc)) { ... } + // const auto now = std::chrono::system_clock::now(); + // auto tp = cctz::time_point<cctz::seconds>::min(); + // cctz::time_zone::civil_transition trans; + // while (tp <= now && nyc.next_transition(tp, &trans)) { + // // transition: trans.from -> trans.to + // tp = nyc.lookup(trans.to).trans; + // } + struct civil_transition { + civil_second from; // the civil time we jump from + civil_second to; // the civil time we jump to + }; + bool next_transition(const time_point<seconds>& tp, + civil_transition* trans) const; + template <typename D> + bool next_transition(const time_point<D>& tp, + civil_transition* trans) const { + return next_transition(detail::split_seconds(tp).first, trans); + } + bool prev_transition(const time_point<seconds>& tp, + civil_transition* trans) const; + template <typename D> + bool prev_transition(const time_point<D>& tp, + civil_transition* trans) const { + return prev_transition(detail::split_seconds(tp).first, trans); + } + + // version() and description() provide additional information about the + // time zone. The content of each of the returned strings is unspecified, + // however, when the IANA Time Zone Database is the underlying data source + // the version() std::string will be in the familar form (e.g, "2018e") or + // empty when unavailable. + // + // Note: These functions are for informational or testing purposes only. + std::string version() const; // empty when unknown + std::string description() const; + + // Relational operators. + friend bool operator==(time_zone lhs, time_zone rhs) { + return &lhs.effective_impl() == &rhs.effective_impl(); + } + friend bool operator!=(time_zone lhs, time_zone rhs) { + return !(lhs == rhs); + } + class Impl; private: explicit time_zone(const Impl* impl) : impl_(impl) {} + const Impl& effective_impl() const; // handles implicit UTC const Impl* impl_; }; -// Relational operators. -bool operator==(time_zone lhs, time_zone rhs); -inline bool operator!=(time_zone lhs, time_zone rhs) { return !(lhs == rhs); } - // Loads the named time zone. May perform I/O on the initial load. // If the name is invalid, or some other kind of error occurs, returns // false and "*tz" is set to the UTC time zone. @@ -184,6 +246,7 @@ time_zone utc_time_zone(); time_zone fixed_time_zone(const seconds& offset); // Returns a time zone representing the local time zone. Falls back to UTC. +// Note: local_time_zone.name() may only be something like "localtime". time_zone local_time_zone(); // Returns the civil time (cctz::civil_second) within the given time zone at @@ -227,7 +290,7 @@ bool parse(const std::string&, const std::string&, const time_zone&, // - %E*f - Fractional seconds with full precision (a literal '*') // - %E4Y - Four-character years (-999 ... -001, 0000, 0001 ... 9999) // -// Note that %E0S behaves like %S, and %E0f produces no characters. In +// Note that %E0S behaves like %S, and %E0f produces no characters. In // contrast %E*f always produces at least one digit, which may be '0'. // // Note that %Y produces as many characters as it takes to fully render the @@ -254,7 +317,7 @@ inline std::string format(const std::string& fmt, const time_point<D>& tp, // Parses an input std::string according to the provided format std::string and // returns the corresponding time_point. Uses strftime()-like formatting // options, with the same extensions as cctz::format(), but with the -// exceptions that %E#S is interpreted as %E*S, and %E#f as %E*f. %Ez +// exceptions that %E#S is interpreted as %E*S, and %E#f as %E*f. %Ez // and %E*z also accept the same inputs. // // %Y consumes as many numeric characters as it can, so the matching data |