How to convert string offset to timespan in c#

Question

I'm trying to convert the convert time to the user's time zone, but I don't have the windows time zone string such as "Pacific Standard Time". All I have is a string offset such as "-07:00". Looks like I need to create a timespan. Is the only way to parse this string manually?. Seems like there should be a way to convert a time using a string offset, but maybe I am missing something.

I have this but it requires the timezone. I'm trying to modify it to use the offset instead, but you can see the timespan that is created for the conversion and I need to get my offset to the timespan.

static void Main(string[] args)
{
    var currentTimeInPacificTime = ConvertUtcTimeToTimeZone(DateTime.UtcNow, "Pacific Standard Time");
    //TimeSpan ts = new TimeSpan("-07:00");
    Console.ReadKey();
}

static DateTimeOffset ConvertUtcTimeToTimeZone(DateTime dateTime, string toTimeZoneDesc)
{
    if (dateTime.Kind != DateTimeKind.Utc) throw new Exception("dateTime needs to have Kind property set to Utc");
    TimeSpan toUtcOffset = TimeZoneInfo.FindSystemTimeZoneById(toTimeZoneDesc).GetUtcOffset(dateTime);
    var convertedTime = DateTime.SpecifyKind(dateTime.Add(toUtcOffset), DateTimeKind.Unspecified);
    return new DateTimeOffset(convertedTime, toUtcOffset);
}

Podgy

Answer 1

You can just use the TimeSpan.Parse method:

TimeSpan ts = TimeSpan.Parse("-07:00");
Console.WriteLine(ts);   // -07:00:00

Be careful to strip a leading "+" as TimeSpan.Parse will fail here. "+01:00" is incorrect, but "01:00" works.

Or if you want be a little more safe, try the TimeSpan.TryParse method:

TimeSpan ts;
if (TimeSpan.TryParse("-07:00", out ts))
    Console.WriteLine(ts);   // -07:00:00

But of course if all you want to do is convert a UTC date/time to a local date/time, you can just do this:

DateTime localDateTime = utcDateTime.ToLocalTime();

Or to convert it to any timezone:

TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById(toTimeZoneDesc);
DateTime localDateTime = TimeZoneInfo.ConvertTime(utcDateTime, tzi);

Cleancut

thanks! So simple too. I didn't think to look for a parse method. – Podgy

The TimeSpan.Parse is correct for that part of the question, but be careful about .ToLocalTime(), because that will be in the time zone of the computer it is running on - which will probably be a server in some other time zone. The last code block is correct, but he said he didn't have a time zone id to input. – Shaitan

This doesn't work if you're offset string contains the + character. This has to be removed first. – Tallow

Answer 2

For more complicated/non-standard formats you can also use TimeSpan.ParseExact(String, String, IFormatProvider), where the second String is a Custom TimeSpan Format String.

API information is available at msdn.microsoft.com, and is linked above.linked.

Orometer

Answer 3

I'm trying to convert the convert time to the user's time zone, but I don't have the windows time zone string such as "Pacific Standard Time". All I have is a string offset such as "-07:00".

Then you don't have what you need to make the correct conversion. Read "Time Zone != Offset" in the timezone tag wiki.

It is important to understand that the "Pacific Standard Time" value is the .Id for the TimeZoneInfo object that is used for US Pacific Time. It covers both Pacific Standard Time (UTC-8) and Pacfic Daylight Time (UTC-7).

All I have is a string offset such as "-07:00". Looks like I need to create a timespan.

Now you have what is commonly called the XY Problem. You shouldn't have any need to work with the offset by itself.

In your code, there is a call to dateTime.Add(toUtcOffset). When doing time zone conversions, this is a code smell that you are doing it wrong. You should never have to manually add or subtract time just to manipulate time zones. That should be reserved for actually changing the moment in time you are talking about.

What you should be doing is to collect a real time zone id from your user. Either "Pacific Standard Time" for use with TimeZoneInfo, or "America/Los_Angeles" for use with a TZDB implementation like Noda Time.

If time zone conversions aren't important in your context, then you might just want to collect a full DateTimeOffset value such as 2013-08-17T13:27:00.000-07:00 instead.

Shaitan

Answer 4

There are time zone strings which includes "Pacific Standard Time". The complete list can be found here. http://www.xiirus.net/articles/article-_net-convert-datetime-from-one-timezone-to-another-7e44y.aspx

Any DateTime object can be converted to some timezone -

    TimeZoneInfo timeZoneInfo; 
    DateTime dateTime ; 

    //Set the time zone information to Pacific Standard Time
    timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time"); 
    //Get date and time in US Mountain Standard Time 
    dateTime = TimeZoneInfo.ConvertTime(DateTime.Now, timeZoneInfo);
    //Print out the date and time
    Console.WriteLine(dateTime.ToString("yyyy-MM-dd HH-mm-ss")); 

So you method can be modified as -

static DateTimeOffset ConvertUtcTimeToTimeZone(DateTime dateTime, string toTimeZoneDesc)
{
   return new DateTimeOffset(TimeZoneInfo.ConvertTime(dateTime, TimeZoneInfo.FindSystemTimeZoneById(toTimeZoneDesc)));
}

Sitwell

You've let the local time zone creep into the conversion by using DateTime.Now, and again by passing an Unspecified kind of DateTime in to the DateTimeOffset constructor. – Shaitan

@MattJohnson - that was just an example, a hint is enough for most people. – Sitwell

Maybe an example of how not to do it... And most people will just copy paste without thinking it through. – Shaitan

Let me be clear, the last two lines should be consolidated to a single line: return TimeZoneInfo.ConvertTime(DateTimeOffset.UtcNow, timeZoneInfo);. This will return a DateTimeOffset where the time and offset are correct for the timeZoneInfo provided. – Shaitan

There were some typos, other that that I don't see any problem with the code. – Sitwell

This is the problem with the .Net API. It leads you in to thinking everything is ok, when it's not. Even after your changes, it's still wrong. The return from TimeZoneInfo.ConvertTime when given a DateTime will be a DateTime with .Kind==DateTimeKind.Unspecified. When pass that in to the new DateTimeOffset(dateTime) constructor, it will erroneously assume that you want the local offset. So the resulting DateTimeOffset will not have the offset that matches the TimeZoneInfo you wanted. – Shaitan

This is why I prefer using Noda Time. It won't let you make these types of errors. It's not your fault - sorry if I sounded harsh. It's the .Net BCL team that came up with this error-prone API. – Shaitan