是否存在Ruby 1.8.7 time.strftime％z错误？

Question

I'm having an issue with Ruby 1.8.7 strftime where the %z is returning the local time after i convert the time to UTC.

I'm doing the following:

>> t = Time.now
=> Mon Dec 19 15:20:16 -0800 2011
>> t.strftime("%z")
=> "-0800"

>> t = Time.now.utc
=> Mon Dec 19 23:20:28 UTC 2011
>> t.strftime("%z")
=> "-0800"

Even after I change the time to UTC, the timezone formatted gets defaulted to my local PST -0800.

Is this a known issue? Is there a way around it?

Answer 1

Note that the fine 1.8.7 manual makes no mention of %z :

...
%w - Day of the week (Sunday is 0, 0..6)
%x - Preferred representation for the date alone, no time
%X - Preferred representation for the time alone, no date
%y - Year without a century (00..99)
%Y - Year with century
%Z - Time zone name
%% - Literal ``%'' character

but the 1.9.3 version does have documented support for %z :

Time zone:
  %z - Time zone as hour and minute offset from UTC (e.g. +0900)
          %:z - hour and minute offset from UTC with a colon (e.g. +09:00)
          %::z - hour, minute and second offset from UTC (e.g. +09:00:00)
  %Z - Time zone abbreviation name

The fact the %z produces anything at all appears to be an undocumented and possibly accidental implementation detail.

You can use %Z in 1.8.7 and 1.9.3; for example, you get these results in 1.8.7:

>> t = Time.now
=> Mon Dec 19 16:46:06 -0800 2011
>> t.zone
=> "PST"
>> t.strftime('%z %Z')
=> "-0800 PST"
>> t = Time.now.utc
=> Tue Dec 20 00:46:27 UTC 2011
>> t.zone
=> "UTC"
>> t.strftime('%z %Z')
=> "-0800 UTC"

That will give you the timezone as UTC, PST, EDT, and similar common abbreviations. If you want the offset, you should be using gmt_offset in both 1.9.3 and 1.8.7 :

>> Time.now.gmt_offset
=> -28800
>> Time.now.utc.gmt_offset
=> 0

Note that gmt_offset gives you the offset in seconds.

Answer 2

Your problem.

ruby-1.9.2-p290 :004 > Time.now.strftime("%z")
 => "-0500" 
ruby-1.9.2-p290 :005 > Time.now.utc.strftime("%z")
 => "+0000"