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

Most of these answers have milliseconds / microseconds which clearly isn't supported by ISO 8601. The correct answer would be:

System.DateTime.Now.ToString("yyyy-MM-ddTHH:mm:ssK");
// or
System.DateTime.Now.ToUniversalTime().ToString("yyyy-MM-ddTHH:mm:ssK");

References:

• ISO 8601 specification
• "K" Specifier

Answer 2

Use:

private void TimeFormats()
{
    DateTime localTime = DateTime.Now;
    DateTime utcTime = DateTime.UtcNow;
    DateTimeOffset localTimeAndOffset = new DateTimeOffset(localTime, TimeZoneInfo.Local.GetUtcOffset(localTime));

    //UTC
    string strUtcTime_o = utcTime.ToString("o");
    string strUtcTime_s = utcTime.ToString("s");
    string strUtcTime_custom = utcTime.ToString("yyyy-MM-ddTHH:mm:ssK");

    //Local
    string strLocalTimeAndOffset_o = localTimeAndOffset.ToString("o");
    string strLocalTimeAndOffset_s = localTimeAndOffset.ToString("s");
    string strLocalTimeAndOffset_custom = utcTime.ToString("yyyy-MM-ddTHH:mm:ssK");

    //Output
    Response.Write("<br/>UTC<br/>");
    Response.Write("strUtcTime_o: " + strUtcTime_o + "<br/>");
    Response.Write("strUtcTime_s: " + strUtcTime_s + "<br/>");
    Response.Write("strUtcTime_custom: " + strUtcTime_custom + "<br/>");

    Response.Write("<br/>Local Time<br/>");
    Response.Write("strLocalTimeAndOffset_o: " + strLocalTimeAndOffset_o + "<br/>");
    Response.Write("strLocalTimeAndOffset_s: " + strLocalTimeAndOffset_s + "<br/>");
    Response.Write("strLocalTimeAndOffset_custom: " + strLocalTimeAndOffset_custom + "<br/>");

}

OUTPUT

UTC
    strUtcTime_o: 2012-09-17T22:02:51.4021600Z
    strUtcTime_s: 2012-09-17T22:02:51
    strUtcTime_custom: 2012-09-17T22:02:51Z

Local Time
    strLocalTimeAndOffset_o: 2012-09-17T15:02:51.4021600-07:00
    strLocalTimeAndOffset_s: 2012-09-17T15:02:51
    strLocalTimeAndOffset_custom: 2012-09-17T22:02:51Z

Sources:

• Standard Date and Time Format Strings (MSDN)

• Custom Date and Time Format Strings (MSDN)

Answer 3

Using Newtonsoft.Json, you can do

JsonConvert.SerializeObject(DateTime.UtcNow)

Example: https://dotnetfiddle.net/O2xFSl

Answer 4

I would just use XmlConvert:

XmlConvert.ToString(DateTime.UtcNow, XmlDateTimeSerializationMode.RoundtripKind);

It will automatically preserve the time zone.

Answer 5

DateTime.Now.ToString("yyyy-MM-dd'T'HH:mm:ss zzz");

DateTime.Now.ToString("O");

NOTE: Depending on the conversion you are doing on your end, you will be using the first line (most like it) or the second one.

Make sure to applied format only at local time, since "zzz" is the time zone information for UTC conversion.

Answer 6

To format like 2018-06-22T13:04:16 which can be passed in the URI of an API use:

public static string FormatDateTime(DateTime dateTime)
{
    return dateTime.ToString("s", System.Globalization.CultureInfo.InvariantCulture);
}