How to parse and generate DateTime objects in ISO 8601 format

Question

There is this SOAP web service that sends me datetime objects in the following format

2016-03-29T12:20:35.093-05:00

That is day 29 of March of year 2016. Hour: 12:20:35.093 (GMT-5).

I want to be able to create a DateTime object, like this:

DateTime.Now

and get the string representation in the format described above and also the inverse operation, create a DateTime from a string like the one given above.

I've tried the following in order to create the date:

new DateTime(2016, 3, 29, 12, 20, 35, 093, DateTimeKind.Utc)

However, I can't not see how to specifie GMT-5 there...

I don't know how to convert a DateTime to the specified string format, either.

Using Nate's code I'm doing the following:

var d = new DateTimeOffset(2016, 3, 29, 12, 20, 35, 93, TimeSpan.FromHours(-3));

FormatIso8601(d)

However this call is returning: "2016-03-29T15:20:35Z" instead of :

"2016-03-29T12:20:35.093-03:00"

which is what I actually need.

I think this works:

        d.ToString("yyyy-MM-ddTHH:mm:ss.fffzzz")

Solution 1

The format you're describing is ISO 8601.

Since you're working with timestamps that inclulde a time zone component, I'd strongly recommend using DateTimeOffset instead of DateTime. It makes things so much easier!

To create a DateTimeOffset for a given date, time, and time zone offset, use this syntax:

var date = new DateTimeOffset(2016, 3, 29, 12, 20, 35, 93, TimeSpan.FromHours(-5));
// March 29, 2016 at 12:20:35.93 GMT-5

This code will format a DateTimeOffset as ISO 8601:

public static string FormatIso8601(DateTimeOffset dto)
{
    string format = dto.Offset == TimeSpan.Zero
        ? "yyyy-MM-ddTHH:mm:ss.fffZ"
        : "yyyy-MM-ddTHH:mm:ss.fffzzz";

    return dto.ToString(format, CultureInfo.InvariantCulture);
}

And, to parse a string back to a DateTimeOffset:

public static DateTimeOffset ParseIso8601(string iso8601String)
{
    return DateTimeOffset.ParseExact(
        iso8601String,
        new string[] { "yyyy-MM-dd'T'HH:mm:ss.FFFK" },
        CultureInfo.InvariantCulture,
        DateTimeStyles.None);
}

If you must get back to a DateTime you can get this from the DateTimeOffset.UtcDateTime property.

Solution 2

A simpler way is to use the ToString method on DateTimeOffset with the "o" argument. This automatically prints the date in ISO8601 format

DateTimeOffset.Now.ToString("o");

The static parse method is also capable of correctly parsing a date in ISO8601 format.

DateTimeOffset.Parse("2016-25-12T20:45:30.3124+01:00");
DateTimeOffset.Parse("2016-25-12T20:45:30.3124Z");

Comments

[Stephen H. Anderson]

Thanks a lot. Is it safe to do this? ParseIso8601(myDate).DateTime to obtain a datetime object? In my system I would need datetimes instead of datetimeoffsets, if possible. Thanks

[Nate Barbettini]

It's possible, but beware of unintended side effects: the time you get will depend on the local time zone of your machine. UtcDateTime will always return a UTC time, if you want to avoid that conversion.

[Stephen H. Anderson]

So it's impossible to obtaina DateTime object which represents the same exact time I passed in the string to ParseIso8601?

[Nate Barbettini]

"Exact time" in which time zone? The string may represent a different time zone than your machine is in.

[Nate Barbettini]

Sure - UtcDateTime will be unambiguous.

[Stephen H. Anderson]

If I do this: var date = new DateTimeOffset(2016, 3, 29, 12, 20, 35, 93, TimeSpan.FromHours(-5)); and then I do date.DateTime would it still be in GMT-5?

[Nate Barbettini]

This is why DateTime sucks. :( It would not necessarily still be GMT-5, it would depend on the time zone of your machine. If your machine is also GMT-5, then yes.

[Nate Barbettini]

No problem. If possible, it's highly recommended to switch everything over to DateTimeOffset.

[Stephen H. Anderson]

Nate, I have a problem with the code given. Please see my edit (I'm publishing it in 5 minutes)