When running strftime ("% G-% m-% d", time () Today, we will get. Why?

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% GNot the year of the Gregorian calendar, but accordingISO-8601: 1988The standard year is calculated by week.

According to this calendar, the firstNot less than 4 days(Week 1 is the first day of a week). It is regarded as the first week. If it is less than four days, the whole week is regarded as the last week of the previous year.

Xelz's MacBook-Air :~ /Tmp [12:21:18] $ php-r'error _ reporting (0); echo strftime ("% G-% V", strtotime ")). "\ n"; '2017-52xelz's MacBook-Air :~ /Tmp [12:21:26] $ php-r'error _ reporting (0); echo strftime ("% G-% V", strtotime ")). "\ n"; '2017-01

The Year to be used.% YOr% Y