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: Gavin Lambert (boost_at_[hidden])
Date: 2019-03-04 22:17:59

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