.ToUniversalTime（）不正确？ [英] .ToUniversalTime() Is Incorrect?

问题描述

  DateTime dt = new DateTime（1972，4，24，0，0，0）; 
 Response.Write（ dt： + dt.ToString（ M / d / yyyy h：mm：ss tt）+< br />）; 
 Response.Write（ dt.Kind： + dt.Kind.ToString（）+< br />））; 
 Response.Write（ dt.ToUniversalTime（）： + dt.ToUniversalTime（）。ToString（ M / d / yyyy h：mm：ss tt）+< br />）; 
  

显示器

  dt：1972年4月24日上午12:00:00 
 dt种类：未指定
 dt.ToUniversalTime（）：1972年4月24日上午7:00:00 
  

这是不正确的。 1972年4月24日太平洋时间实际上是1972年4月24日世界标准时间。

我已经通过iOS内部的UTC日期对话和www确认了正确的UTC转换。 timeanddate.com和UTC时间应该是8 AM。我在做错什么吗？

服务器在太平洋时间时区运行，因此ToUniversalTime应该从太平洋时区转换为UTC，因为未指定被视为本地。 p>

解决方案

如果您使用的不是太平洋标准时间的计算机，则可以使用以下代码查看此行为：

  DateTime dt = new DateTime（1972，4，24，0，0，0）; 
 TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById（太平洋标准时间）; 
 
 Console.WriteLine（TimeZoneInfo.ConvertTimeToUtc（dt，tz））; 
 // 1972年4月24日7:00:00 
  

，它可以正确处理此特殊情况：

  var pacific = DateTimeZoneProviders.Tzdb [ America / Los_Angeles]; 
 
 LocalDateTime localDateTime = new LocalDateTime（1972，4，24，0，0）; 
 ZonedDateTime zonedDateTime = pacific.AtStrictly（localDateTime）; 
 
 DateTime utcDateTime = zonedDateTime.ToDateTimeUtc（）; 
 
 Console.WriteLine（utcDateTime）; 
 // 1972年4月24日8:00:00 
  

    DateTime dt = new DateTime(1972, 4, 24, 0, 0, 0);
    Response.Write("dt: " + dt.ToString("M/d/yyyy h:mm:ss tt") + "<br />");
    Response.Write("dt.Kind: " + dt.Kind.ToString() + "<br />");
    Response.Write("dt.ToUniversalTime(): " + dt.ToUniversalTime().ToString("M/d/yyyy h:mm:ss tt") + "<br />");

displays

dt: 4/24/1972 12:00:00 AM
dt.Kind: Unspecified
dt.ToUniversalTime(): 4/24/1972 7:00:00 AM

which is incorrect. April 24, 1972 at 12 PM Pacific is actually April 24, 1972 at 8 AM UTC.

I have confirmed the correct UTC conversion with iOS's internal UTC date conversation and www.timeanddate.com and the UTC time should be 8 AM. Am I doing something wrong?

The server is running in "Pacific Time" timezone so ToUniversalTime should be converting from Pacific timezone to UTC since Unspecified is treated like Local.

解决方案

If you're on a machine that's not on Pacific Standard Time, you can see this behavior using the following code:

DateTime dt = new DateTime(1972, 4, 24, 0, 0, 0);    
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");

Console.WriteLine (TimeZoneInfo.ConvertTimeToUtc(dt, tz));
// 4/24/1972 7:00:00 AM

If you look at navy.mil's history of daylight saving time, you'll notice the following paragraph:

The Uniform Time Act of 1966 provided standardization in the dates of beginning and end of daylight time in the U.S. but allowed for local exemptions from its observance. The act provided that daylight time begin on the last Sunday in April and end on the last Sunday in October, with the changeover to occur at 2 a.m. local time.

And then a little later on:

In 1986, a law was passed that shifted the starting date of daylight time to the first Sunday in April, beginning in 1987

So the DST switchover wasn't the first Sunday in April until 1987, but for some reason .NET is acting as if it was.

Timeanddate.com's history of DST seems to agree, and lists April 30, 1972 (the last Sunday in April) as the date clocks were turned forward one hour (to UTC-7).

Microsoft's DST adjustment rules for times before 1987 appear to be wrong (and I'm not the only one who thinks so).

Here's what TimeZoneInfo lists as the rules for PST:

Basically, Microsoft has ignored the historical rules and chosen to use rules put into effect in 1987 for dates that happened before those rules even existed.

Essentially your date (in 1972) is being handled incorrectly by Microsoft's TimeZoneInfo adjustment rules.

If you're looking for a library that handles these types of time zone rules much better, check out NodaTime, which handles this particular case correctly:

var pacific = DateTimeZoneProviders.Tzdb["America/Los_Angeles"];

LocalDateTime localDateTime = new LocalDateTime(1972, 4, 24, 0, 0);
ZonedDateTime zonedDateTime = pacific.AtStrictly(localDateTime);

DateTime utcDateTime = zonedDateTime.ToDateTimeUtc();

Console.WriteLine(utcDateTime);
// 4/24/1972 8:00:00 AM

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