Question

我想创建一个NSDateFormatter来解析这样的日期“2014-05-13 23：31：41.374577”。所以：

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss.SSSSSS";
NSString *dateString = @"2014-05-13 23:31:41.374577";
NSDate *date = [formatter dateFromString:dateString];
NSString *anotherDateString = [formatter stringFromDate:date];

但是，anotherDateString为2014-05-13 23:31:41.374000。为什么它会截断毫秒？

Answer 1

似乎NSDateFormatter仅适用于毫秒分辨率原因如下：

通过在CFDateFormatterCreateDateFromString中设置断点，可以看到这个函数是从dateFromString:调用的：

(lldb) bt
* thread #1: tid = 0x26d03f, 0x018f47d0 CoreFoundation`CFDateFormatterCreateDateFromString, queue = 'com.apple.main-thread', stop reason = breakpoint 3.1
    frame #0: 0x018f47d0 CoreFoundation`CFDateFormatterCreateDateFromString
    frame #1: 0x0116e0ea Foundation`getObjectValue + 248
    frame #2: 0x0116dfc7 Foundation`-[NSDateFormatter getObjectValue:forString:errorDescription:] + 206
    frame #3: 0x0116879f Foundation`-[NSDateFormatter dateFromString:] + 71
  * frame #4: 0x00002d56 foo`main(argc=1, argv=0xbfffee54) + 182 at main.mm:25

CFDateFormatterCreateDateFromString()来自 CFDateFormatter.c 这是开源的。可以看到所有的日历计算都是使用 ICU Calendar Classes

在calendar.h中声明Calendar使用UDate，其分辨率为毫秒级：

/**
 * <code>Calendar</code> is an abstract base class for converting between
 * a <code>UDate</code> object and a set of integer fields such as
 * <code>YEAR</code>, <code>MONTH</code>, <code>DAY</code>, <code>HOUR</code>,
 * and so on. (A <code>UDate</code> object represents a specific instant in
 * time with millisecond precision. See UDate
 * for information about the <code>UDate</code> class.)
 * ...

NSDateFormatter毫秒bug

1 个答案: