Parse time with strptime using Time.zone

Question

I am trying to parse a datetime with Time class in Ruby 2.0. I can't figure out how to parse date and get it in a specified timezone. I have used Time.zone.parse to parse a date where I first call Time.zone and set it to a specified timezone. In the below example, I set the zone but it does not effect strptime, I have tried doing Time.zone.parse(date) but I can't get it parse a date like the one below.

Time.zone = "Central Time (US & Canada)"
#=> "Central Time (US & Canada)"
irb(main):086:0> Time.strptime("08/26/2013 03:30 PM","%m/%d/%Y %I:%M %p")
#=> 2013-08-26 15:30:00 -0400

Answer 1

Time.zone isn’t a part of Ruby, it’s a part of ActiveSupport (which is included with Rails). As such, strptime does not know about Time.zone at all. You can, however, convert a normal Ruby Time into an ActiveSupport::TimeWithZone using in_time_zone, which uses Time.zone’s value by default:

require 'active_support/core_ext/time'
Time.zone = 'Central Time (US & Canada)'

time = Time.strptime('08/26/2013 03:30 PM', '%m/%d/%Y %I:%M %p')
#=> 2013-08-26 15:30:00 -0400
time.in_time_zone
#=> Mon, 26 Aug 2013 14:30:00 CDT -05:00

Answer 2

If you are only looking at Ruby2.0, you may find the time lib useful:

require 'time'
time.zone # return your current time zone

a = Time.strptime("08/26/2013 03:30 PM","%m/%d/%Y %I:%M %p")
# => 2013-08-26 15:30:00 +1000
a.utc  # Convert to UTC
a.local # Convert back to local
# Or you can add/subtract the offset for the specific time zone you want:
a - 10*3600 which gives UTC time too

Answer 3

strptime gets its parameters from the time string. As such, the time string must contain time zone information.

If you are parsing time strings in a specific time zone, but the time strings that you receive do not have it embedded - then you can add time zone information before passing the time string to srtptime, and asking strptime to parse the time zone offset using %z or name using %Z.

In a nutshell, if you have a time string 08/26/2013 03:30 PM and you want it parsed in the UTC time zone, you would have:

str = '08/26/2013 03:30 PM'
Time.strptime("#{str} UTC}", "%m/%d/%Y %I:%M %p %Z")