convert separate year, month, day, hour, minute, secs, ms to milliseconds since epoch
I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have: int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? } Is there a better way? Could not figure out how to use boost::chrono :( Something else? Kind Regards, Vic
On 4/03/2019 09:45, Victor Yankee wrote:
I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have:
int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? }
timegm is not cross platform. mktime is, but uses local time instead of UTC.
Is there a better way? Could not figure out how to use boost::chrono :( Something else?
Boost.Chrono is for time intervals, not dates. Boost.DateTime, however, has the ptime class which will solve this for you.
On 04.03.2019 23:17, Gavin Lambert via Boost-users wrote:
On 4/03/2019 09:45, Victor Yankee wrote:
I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have:
int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? }
timegm is not cross platform. mktime is, but uses local time instead of UTC.
Is there a better way? Could not figure out how to use boost::chrono :( Something else?
Boost.Chrono is for time intervals, not dates.
Boost.DateTime, however, has the ptime class which will solve this for you.
I think with C++11 something like: std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count() might also do the trick. Cheers, Leon
On 05.03.2019 00:40, Leon Mlakar wrote:
On 04.03.2019 23:17, Gavin Lambert via Boost-users wrote:
On 4/03/2019 09:45, Victor Yankee wrote:
I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have:
int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? }
timegm is not cross platform. mktime is, but uses local time instead of UTC.
Is there a better way? Could not figure out how to use boost::chrono :( Something else?
Boost.Chrono is for time intervals, not dates.
Boost.DateTime, however, has the ptime class which will solve this for you.
I think with C++11 something like:
std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count()
might also do the trick.
Cheers,
Leon
Err, then again, it might not until C++20. C++11 embarrassingly failed to state what the Epoch is. So for now clocks are free to use their own and currently the above is useless for cross-platform applications (but so is timegm). I wonder how this works on Windows with VS2019? Cheers, Leon
On Tue, 5 Mar 2019 at 01:51, Leon Mlakar via Boost-users < boost-users@lists.boost.org> wrote:
I wonder how this works on Windows with VS2019?
It returns 1551766256847 (so the same as https://www.epochconverter.com/, i.e. "Unix Time"), there's no reason to assume it returns something else with VS2019 (AFAICS), until/unless it supports C++20 and the std explicitly changes the behavior (forces MS to break backward compatibility), you can be assured that it will be doing that for a while (until the Y38 problem raises its head). degski -- *"Big boys don't cry" - **Eric Stewart, Graham Gouldman*
On 05.03.2019 07:11, degski via Boost-users wrote:
On Tue, 5 Mar 2019 at 01:51, Leon Mlakar via Boost-users <boost-users@lists.boost.org <mailto:boost-users@lists.boost.org>> wrote:
I wonder how this works on Windows with VS2019?
It returns 1551766256847 (so the same as https://www.epochconverter.com/, i.e. "Unix Time"), there's no reason to assume it returns something else with VS2019 (AFAICS), until/unless it supports C++20 and the std explicitly changes the behavior (forces MS to break backward compatibility), you can be assured that it will be doing that for a while (until the Y38 problem raises its head).
Thank you for the information. Behid the question was my, obviously incorrect, assumption that older visual studio versions, from times when c++20 was not yet conceived and epoch thus not set to Jan 1 AD 1970, are using some different epoch - as Microsoft frequently did, like Jan 1 AD 1 (.NET), Jan 1 AD 1601 (NTFS), Jan 1 AD 1980 (DOS, FAT family of file systems). So seeing Microsoft embracing a standard thing like posix epoch without screaming and kicking is a nice surprise. And it was late. Cheers, Leon P.S. As for the Y38, std::chrono should be okay as it's not bound to 32-bit integrals.
On Tue, 5 Mar 2019 at 10:39, Leon Mlakar via Boost-users < boost-users@lists.boost.org> wrote:
Behid the question was my, obviously incorrect, assumption that olde visual studio versions, from times when c++20 was not yet conceived and epoch thus not set to Jan 1 AD 1970, are using some different epoch - as Microsoft frequently did, like Jan 1 AD 1 (.NET), Jan 1 AD 1601 (NTFS),
MS just implements the standard [in this case] and for timings within Windows (i..e. Windows.h), they have the FILETIME API, " Jan 1 AD 1 (.NET), Jan 1 AD 1601 (NTFS)", etc (possibly because they realized the world was not created in 1970, but heck who knows).
Jan 1 AD 1980 (DOS, FAT family of file systems). So seeing Microsoft embracing a standard thing like posix epoch without screaming and kicking is a nice surprise.
Well at the time of DOS, there was no std, so one could forgive them (on this occasion) to not implement it correctly. degski -- *"Big boys don't cry" - **Eric Stewart, Graham Gouldman*
On Sun, 3 Mar 2019 12:45:17 -0800 Victor Yankee via Boost-users <boost-users@lists.boost.org> wrote:
I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have:
int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? }
Is there a better way?
time_tsec_since_epoch(int year, int month, int day, int hour, int minute, int second) { static const boost::posix_time::ptime epoch(boost::gregorian::date(1970,1,1)); boost::posix_time::ptime pt( boost::gregorian::date(year, month, day), boost::posix_time::time_duration(hour, minute, second) ); boost::posix_time::time_duration since_epoch = pt - epoch; return since_epoch.total_seconds(); } -- Best regards, Sergey Spiridonov
On Sun, 3 Mar 2019 12:45:17 -0800 Victor Yankee via Boost-users <boost-users@lists.boost.org> wrote:
I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have:
int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? }
Is there a better way?
Sorry, previous was for seconds #include <boost/date_time/posix_time/posix_time.hpp> int64_t time_msec_since_epoch(int year, int month, int day, int hour, int minute, int second, int msec) { static const boost::posix_time::ptime epoch(boost::gregorian::date(1970,1,1)); boost::posix_time::ptime pt( boost::gregorian::date(year, month, day), boost::posix_time::time_duration(hour, minute, second) + boost::posix_time::milliseconds(msec) ); boost::posix_time::time_duration since_epoch = pt - epoch; return since_epoch.total_milliseconds(); } -- Best regards, Sergey Spiridonov
participants (5)
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degski -
Gavin Lambert -
Leon Mlakar -
Sergey Spiridonov -
Victor Yankee