Given a DateTime object, how do I get an ISO 8601 date in string format?

Question

Given:

DateTime.UtcNow

How do I get a string which represents the same value in an ISO 8601-compliant format?

Note that ISO 8601 de

Answer 1

System.DateTime.UtcNow.ToString("o")

=>

val it : string = "2013-10-13T13:03:50.2950037Z"

Answer 2

You have a few options including the "Round-trip ("O") format specifier".

var date1 = new DateTime(2008, 3, 1, 7, 0, 0);
Console.WriteLine(date1.ToString("O"));
Console.WriteLine(date1.ToString("s", System.Globalization.CultureInfo.InvariantCulture));

Output

2008-03-01T07:00:00.0000000
2008-03-01T07:00:00

However, DateTime + TimeZone may present other problems as described in the blog post DateTime and DateTimeOffset in .NET: Good practices and common pitfalls:

DateTime has countless traps in it that are designed to give your code bugs:

1.- DateTime values with DateTimeKind.Unspecified are bad news.

2.- DateTime doesn't care about UTC/Local when doing comparisons.

3.- DateTime values are not aware of standard format strings.

4.- Parsing a string that has a UTC marker with DateTime does not guarantee a UTC time.

Answer 3

To convert DateTime.UtcNow to a string representation of yyyy-MM-ddTHH:mm:ssZ, you can use the ToString() method of the DateTime structure with a custom formatting string. When using custom format strings with a DateTime, it is important to remember that you need to escape your seperators using single quotes.

The following will return the string represention you wanted:

DateTime.UtcNow.ToString("yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'", DateTimeFormatInfo.InvariantInfo)

Answer 4

You can get the "Z" (ISO 8601 UTC) with the next code:

Dim tmpDate As DateTime = New DateTime(Now.Ticks, DateTimeKind.Utc)
Dim res as String = tmpDate.toString("o") '2009-06-15T13:45:30.0000000Z

Here is why:

The ISO 8601 have some different formats:

DateTimeKind.Local

2009-06-15T13:45:30.0000000-07:00

DateTimeKind.Utc

2009-06-15T13:45:30.0000000Z

DateTimeKind.Unspecified

2009-06-15T13:45:30.0000000

.NET provides us with an enum with those options:

'2009-06-15T13:45:30.0000000-07:00
Dim strTmp1 As String = New DateTime(Now.Ticks, DateTimeKind.Local).ToString("o")

'2009-06-15T13:45:30.0000000Z
Dim strTmp2 As String = New DateTime(Now.Ticks, DateTimeKind.Utc).ToString("o")

'2009-06-15T13:45:30.0000000
Dim strTmp3 As String = New DateTime(Now.Ticks, DateTimeKind.Unspecified).ToString("o")

Note: If you apply the Visual Studio 2008 "watch utility" to the toString("o") part you may get different results, I don't know if it's a bug, but in this case you have better results using a String variable if you're debugging.

Source: Standard Date and Time Format Strings (MSDN)

Answer 5

DateTime.UtcNow.ToString("s")

Returns something like 2008-04-10T06:30:00

UtcNow obviously returns a UTC time so there is no harm in:

string.Concat(DateTime.UtcNow.ToString("s"), "Z")

Answer 6

As mentioned in other answer, DateTime has issues by design.

NodaTime

I suggest to use NodaTime to manage date/time values:

• Local time, date, datetime
• Global time
• Time with timezone
• Period
• Duration

Formatting

So, to create and format ZonedDateTime you can use the following code snippet:

var instant1 = Instant.FromUtc(2020, 06, 29, 10, 15, 22);

var utcZonedDateTime = new ZonedDateTime(instant1, DateTimeZone.Utc);
utcZonedDateTime.ToString("yyyy-MM-ddTHH:mm:ss'Z'", CultureInfo.InvariantCulture);
// 2020-06-29T10:15:22Z


var instant2 = Instant.FromDateTimeUtc(new DateTime(2020, 06, 29, 10, 15, 22, DateTimeKind.Utc));

var amsterdamZonedDateTime = new ZonedDateTime(instant2, DateTimeZoneProviders.Tzdb["Europe/Amsterdam"]);
amsterdamZonedDateTime.ToString("yyyy-MM-ddTHH:mm:ss'Z'", CultureInfo.InvariantCulture);
// 2020-06-29T12:15:22Z

For me NodaTime code looks quite verbose. But types are really useful. They help to handle date/time values correctly.

Newtonsoft.Json

To use NodaTime with Newtonsoft.Json you need to add reference to NodaTime.Serialization.JsonNet NuGet package and configure JSON options.

services
    .AddMvc()
    .AddJsonOptions(options =>
    {
        var settings=options.SerializerSettings;
        settings.DateParseHandling = DateParseHandling.None;
        settings.ConfigureForNodaTime(DateTimeZoneProviders.Tzdb);
    });