Ruby On Rails, week number is not the correct one (-1)

问题

I need the current week number, if I'm not totally mistaken it's week 51 right now? However when testing it in the console I get this.

Time.now
=> 2013-12-19 11:08:25 +0100
Time.now.strftime('%U')
=> "50"

Date.today
=> Thu, 19 Dec 2013
Date.today.strftime("%U").to_i
=> 50

Why is that?

回答1:

Time.now.strftime('%V') will give you the week number according to ISO 8601.

回答2:

why is that?

according to %U or %W, The days in the year before the first week are in week 0 (00..53).

with %V (as @Graeme McLean wrote), The days in the year before the first week are in the last week of the previous year (01..53).

From here.

回答3:

Hmm, I'm unsure as to why it is that way, but to get the correct one using Ruby, I use this:

require 'Date'

week_number = Date.today.cweek #=> 51

来源：https://stackoverflow.com/questions/20678784/ruby-on-rails-week-number-is-not-the-correct-one-1