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System_clock::time_point this_morning = today ĭays days_since_epoch = today - unix_epoch (Howard Hinnant was one of the guys that worked on the C++11 library.) auto now = system_clock::now() As long as there are no leap seconds between the system epoch and (system time zone), or within an equal amount of time in the other direction from the system epoch, then any counted leap seconds should cancel out and l will be wrong in just the way that unix timestamps are wrong.Īnother option is to use a decent date library such as Howard Hinnant's chrono::date. L should now represent the (wrong) number of seconds since UTC. the number of seconds since the system epoch (again, leap seconds
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Treat the new calendar time as offset time in the local TZ. much as UTC differs from the local timezone. represents a time offset from the original calendar time by as original, but if we change the timezone to the system TZ then it as UTC this represents the same calendar date and time as the get a calender time for that time_point in UTC. number of seconds since your system's epoch (leap seconds may treat it as (your system's time zone) and get the You would not get a time point actually corresponding to 00:00:00+0000.Īs Andy Prowl suggests you could do something silly like: // (no time zone) Or if you did something like: std::chrono::steady_clock::now() - unix_timestamp For example subtracting unix timestamps does not give you an accurate count of seconds between the times. Just remember that these values aren't real times, so you can't in general use unix timestamps in arithmetic.
#Chrome utc clock portable#
So although not specified in C++ there is an easy and widely portable way to get a Unix timestamp: auto unix_timestamp = std::chrono::seconds(std::time(NULL)) Īnd if you want a number of milliseconds since UTC (similarly not counting all of them) then you can do this: int unix_timestamp_x_1000 = std::chrono::milliseconds(unix_timestamp).count() Similar documentation can be found for other systems, such as AIX, HP-UX, Solaris, etc.
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ISO/IEC 9945-1:1996 (POSIX.1'') provided the selected local timezoneĭoes not contain a leap-second table (see zic(8)).
#Chrome utc clock iso#
The asctime(), ctime(), difftime(), gmtime(), localtime(), and mktime()įunctions conform to ISO/IEC 9899:1990 ( ISO C90''), and conform to The functions ctime(), gmtime(), and localtime() all take as an argumentĪ time value representing the time in seconds since the Epoch (00:00:00 The time function returns the number of seconds elapsed since midnight (00:00:00), January 1, 1970, Coordinated Universal Time (UTC), according to the system clock. The intention is that the interpretation of seconds since the Epoch values be consistent see POSIX.1-2008 Rationale A.4.15 for further rationale. This value is not the same as the actual number of seconds between the time and the Epoch, because of leap seconds and because system clocks are not required to be synchronized to a standard reference. This formula takes account of the facts that all years that are evenly divisible by 4 are leap years, but years that are evenly divisible by 100 are not leap years unless they are also evenly divisible by 400, in which case they are leap years. POSIX.1 defines seconds since the Epoch using a formula that approximates the number of seconds between a specified time and the Epoch. Time() returns the time as the number of seconds since the Epoch, 00:00:00 +0000 (UTC). This is somewhat ridiculous and one has to wonder what the point of it is, so I agree that this is a silly question.Īnyway, lets look at some platform documentation for time_t and time(). A unix time stamp is defined as the number of seconds since JanuUTC, except not counting all the seconds.