Where s the DateTime Z format specifier

Question

Update  Format specifiers are not the same thing as format strings  a format specifier is a piece of a custom format string  where a format string is  stock  and doesn t provide customization  My problem is with specifiers not formats   I ve been trying to perform roundtrip DateTime conversions with a format string that uses  zzz  format specifier  which I know is bound to local time  So  if I attempt to round trip with a UTC date time it throws a DateTimeInvalidLocalFormat exception  which it should  with this text   A UTC DateTime is being converted to text in a format that is only correct for local times  This can happen when calling DateTime ToString using the  z  format specifier  which will include a local time zone offset in the output  In that case  either use the  Z  format specifier  which designates a UTC time  or use the  o  format string  which is the recommended way to persist a DateTime in text  This can also occur when passing a DateTime to be serialized by XmlConvert or DataSet  If using XmlConvert ToString  pass in XmlDateTimeSerializationMode RoundtripKind to serialize correctly  If using DataSet  set the DateTimeMode on the DataColumn object to DataSetDateTime Utc   Based on this suggestion  all I need to do to get my code to work is to replace  zzz  with  ZZZ  so I can stand in a UTC format  The problem is   Z  isn t found anywhere in the documentation and any  Z  format combination I try  i e   Z    ZZ    ZZZ   always just converts the DateTime instance with those Z s treated like literals   Did someone forget to implement  Z  without telling the exception message author  or am I missing how to swap out a valid local time offset with   0000  without hacking   Code Example      This is the format with  zzzzz  representing local time offset const string format    ddd MMM dd HH mm ss zzzzz yyyy       create a UTC time const string expected    Fri Dec 19 17 24 18  0000 2008   var time   new DateTime 2008  12  19  17  24  18  0  DateTimeKind Utc       If you re using a debugger this will rightfully throw an exception    with  NET 3 5 SP1 because  z  is for local time only  however  the exception    asks me to use the  Z  specifier for UTC times  but it doesn t exist  so it    just spits out  Z  as a literal  var actual   time ToString format  CultureInfo InvariantCulture    Assert AreEqual expected  actual

User · Accepted Answer

Maybe the  K  format specifier would be of some use   This is the only one that seems to mention the use of capital  Z     Z  is kind of a unique case for DateTimes   The literal  Z  is actually part of the ISO 8601 datetime standard for UTC times   When  Z   Zulu  is tacked on the end of a time  it indicates that that time is UTC  so really the literal Z is part of the time   This probably creates a few problems for the date format library in  NET  since it s actually a literal  rather than a format specifier

User · Answer

Round tripping dates through strings has always been a pain   but the docs to indicate that the  o  specifier is the one to use for round tripping which captures the UTC state  When parsed the result will usually have Kind    Utc if the original was UTC  I ve found that the best thing to do is always normalize dates to either UTC or local prior to serializing then instruct the parser on which normalization you ve chosen   DateTime now   DateTime Now  DateTime utcNow   now ToUniversalTime     string nowStr   now ToString   o     string utcNowStr   utcNow ToString   o      now   DateTime Parse  nowStr    utcNow   DateTime Parse  nowStr  null  DateTimeStyles AdjustToUniversal     Debug Assert  now    utcNow

User · Answer

Label1 Text   dt ToString  quot dd MMM yyyy   hh mm   ff   zzz   zz   z quot     will output  07 Mai 2009   08 16   13    02 00    02    2  I m in Denmark  my Offset from GMT is  2 hours  witch is correct  if you need to get the CLIENT Offset  I recommend that you check a little trick that I did  The Page is in a Server in UK where GMT is  00 00 and  as you can see you will get your local GMT Offset   Regarding you comment  I did  DateTime dt1   DateTime Now  DateTime dt2   dt1 ToUniversalTime     Label1 Text   dt1 ToString  quot dd MMM yyyy   hh mm   ff   zzz   zz   z quot    Label2 Text   dt2 ToString  quot dd MMM yyyy   hh mm   FF   ZZZ   ZZ   Z quot     and I get this  07 Mai 2009   08 24   14    02 00    02    2 07 Mai 2009   06 24   14   ZZZ   ZZ   Z   I get no Exception  just     it does nothing with capital Z    I m sorry  but am I missing something   Reading carefully the MSDN on Custom Date and Time Format Strings there is no support for uppercase  Z

User · Answer

I was dealing with DateTimeOffset and unfortunately the  o  prints out   0000  not  Z    So I ended up with   dateTimeOffset UtcDateTime ToString  o

User · Answer

This page on MSDN lists standard DateTime format strings  uncluding strings using the  Z    Update  you will need to make sure that the rest of the date string follows the correct pattern as well  you have not supplied an example of what you send it  so it s hard to say whether you did or not   For the UTC format to work it should look like this      yyyy - MM - dd HH   mm   ss Z  DateTime utcTime   DateTime Parse  2009-05-07 08 17 25Z

User · Answer

When you use DateTime you are able to store a date and a time inside a variable   The date can be a local time or a UTC time  it depend on you   For example  I m in Italy   2 UTC   var dt1   new DateTime 2011  6  27  12  0  0      store 2011-06-27 12 00 00 var dt2   dt1 ToUniversalTime       store 2011-06-27 10 00 00   So  what happen when I print dt1 and dt2 including the timezone   dt1 ToString  MM dd yyyy hh mm ss z       Compiler alert       Output  06 27 2011 12 00 00  2  dt2 ToString  MM dd yyyy hh mm ss z       Compiler alert       Output  06 27 2011 10 00 00  2   dt1 and dt2 contain only a date and a time information  dt1 and dt2 don t contain the timezone offset   So where the   2  come from if it s not contained in the dt1 and dt2 variable   It come from your machine clock setting   The compiler is telling you that when you use the  zzz  format you are writing a string that combine  DATE   TIME   that are store in dt1 and dt2     TIMEZONE OFFSET   that is not contained in dt1 and dt2 because they are DateTyme type  and it will use the offset of the server machine that it s executing the code   The compiler tell you  Warning  the output of your code is dependent on the machine clock offset   If i run this code on a server that is positioned in London   1 UTC  the result will be completly different  instead of   2  it will write   1       dt1 ToString  MM dd yyyy hh mm ss z       Output  06 27 2011 12 00 00  1  dt2 ToString  MM dd yyyy hh mm ss z       Output  06 27 2011 10 00 00  1   The right solution is to use DateTimeOffset data type in place of DateTime  It s available in sql Server starting from the 2008 version and in the  Net framework starting from the 3 5 version

[c#] Where's the DateTime 'Z' format specifier?

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