NSDateFormatter中'YYYY'和'yyyy'之间的区别 [英] Difference between 'YYYY' and 'yyyy' in NSDateFormatter

问题描述

'YYYY'和'yyyy'之间的确切区别是什么？我在中读到这个链接，它表明

What is exact difference between 'YYYY' and 'yyyy'. I read in this link, it states that

常见的错误是使用YYYY。 yyyy指定日历年
而YYYY指定年份（年度周），用于ISO
年周历。在大多数情况下，yyyy和YYYY会产生相同的
数，但它们可能会有所不同。通常你应该使用
日历年。

A common mistake is to use YYYY. yyyy specifies the calendar year whereas YYYY specifies the year (of "Week of Year"), used in the ISO year-week calendar. In most cases, yyyy and YYYY yield the same number, however they may be different. Typically you should use the calendar year.

但是当我尝试使用

NSString *stringDate = @"Feb 28, 2013 05:30pm";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"MMM dd, yyyy hh:mma"];
NSDate *date=[dateFormatter dateFromString:stringDate];
NSLog(@"Date 1 : %@",date); //2013-02-28 12:00:00 +0000

NSString *stringDatee = @"Feb 28, 2013 05:30pm";
NSDateFormatter *dateFormatterr = [[NSDateFormatter alloc] init];
[dateFormatterr setDateFormat:@"MMM dd, YYYY hh:mma"];
NSDate *datee=[dateFormatterr dateFromString:stringDatee];
NSLog(@"Date 2 : %@",datee); //2013-01-05 12:00:00 +0000

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"MMM dd, YYYY hh:mma"];
NSString *dateString = [dateFormat stringFromDate:datee];
NSLog(@"date 3 : %@", dateString); //Jan 05, 2013 05:30PM

在此处，结果为日期和 datee 不同，我理解，但为什么日期2和日期3的结果不同？当我从字符串创建日期并再次将其反转为字符串，但输出不匹配？

As here, result to date and datee different, which I understood, but why result of date 2 and date 3 are different? As I am creating date from string and reversing same to string again, but output mismatches?

有没有人知道相同的原因？虽然它指定了一年中的一周，但我仍然应该得到相同的结果。

Has anybody knows reason about same?. Though it specifies week of year, still I should get result same.

谢谢..

编辑： -

如果我编码

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"MMM dd, YYYY hh:mma"];
NSString *dateString = [dateFormatterr stringFromDate:[NSDate date]];
NSLog(@"date: %@", dateString); //Feb 28, 2013 04:37PM

如果结果是正确的结果，但我传递的结果相同字符串到目前为止我得到 2013-01-05 12:00:00 +0000 ，检查NSLog的日期2，奇怪的结果，为什么？

If results me proper result, but same which I pass as string to date I get 2013-01-05 12:00:00 +0000, check date 2 of NSLog, Strange result, why?

推荐答案

使用正确格式的日期格式字符串也很重要。

Also when using a date format string using the correct format is important.

@YYYY是基于周的日历年。

@"YYYY" is week-based calendar year.

@yyyy是普通的日历年。

@"yyyy" is ordinary calendar year.

你可以通过整个博客，很好看看它

You can go through the whole blog, its a good to give it a look

http://realmacsoftware.com/blog/working-with-date-and-time

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