Re: [Boost-users] convert separate year, month, day, hour, minute, secs, ms to milliseconds since epoch

Subject: Re: [Boost-users] convert separate year, month, day, hour, minute, secs, ms to milliseconds since epoch
From: Leon Mlakar (leon_at_[hidden])
Date: 2019-03-04 23:40:21

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)
>> Â Â Â Â Â Â Â Â Â Â Â Â  {
>> Â Â Â Â Â Â Â Â Â Â Â Â  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;
>> Â Â Â Â Â Â Â Â Â Â Â Â  return (1000* timegm(&t))+ms; // is timegm cross-platform?
>> Â Â Â Â Â Â Â Â Â Â Â Â  }
>
> 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