得到月份的最后一天

How would I get the last day of a current month given the month number.

如果给出月份数，我将如何获得当月的最后一天。

For example if the month is 8 (August 2014), how would I get the last day of the month? (The last day of August is the 31th). The function(8) would return 31.

例如，如果月份是8（2014年8月），我将如何获得该月的最后一天？（8月的最后一天是31日）。函数（8）将返回31。

Thank you for the help.

感谢您的帮助。

2 个解决方案

#1

Using Date::civil:

使用Date :: civil：

require 'date'
Date.civil(2014, 8, -1).day
# => 31

According to the documentation:

根据文件：

The month and the day of month should be a negative or a positive number (as a relative month/day from the end of year/month when negative). They should not be zero.

月份和月份应为负数或正数（作为从年末/月结束时的相对月/日）。它们不应该是零。

#2

require 'date'
def function(month)
  raise "invalid month" unless month.is_a?(Integer) and month.between?(1, 12)
  month == 12 ? 31 : Date.new(Date.today.year,month+1,1).prev_day.day
end
function(8)
# => 31

source: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/Date.html#method-i-prev_day

来源：http：//www.ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/Date.html#method-i-prev_day

#1