Re: Converting the time from one timezone to another

Did you read my posting? I understand the concept of UTC, and the process of
getting from servertime to localtime (I even showed the code for this in my
posting). My question is "Does .NET have a way of telling me how many hours
to subtract, perhaps a function that returns the number of hours to
add/subtract from UTC that might be something like this:

UtcOffsetForTimezone("EST") would return -5

If I wanted to get the local time for Eastern Standard Time, I could very
easily just use


Date.UtcNow.AddHours(-5)


The reason I don't like this method is because since most people know what
timezone they live in by it's name rather than it's UTC offset, I would like
a way to enter the timezone as a parameter in order to find the offset.
Sure, I could lookup all the timezones and their offsets myself, but I would
expect this to already be a part of ASP.NET. This may sound lazy, but if you
look at all the other things that are easy but ASP.NET have done for you,
it's not an unreasonable thing to ask.
--
Nathan Sokalski
njsokalski@xxxxxxxxxxx
http://www.nathansokalski.com/

"Stephany Young" <noone@localhost> wrote in message
news:OVjtB6MNGHA.1716@xxxxxxxxxxxxxxxxxxxxxxx
Given the other newsgroups you cross-posted to, I have to assume that you
are talking about an ASP.NET application running on a web server halfway
around the world, and that your reference to 'local' actually refers to
the machine upon which you are viewing the generated 'page' in a web
browser.

Working on that principle, I also assume that you want to either:

1. Carry out some calculation at the server using a date/time pasesed
from the client that represents the a point in time at the client
expressed in terms of the time zone where the server is physically
situated,

or

2. Carry out some calculation at the client using a date/time passed
from the server that represents a point of time at the server
expressed in terms of the time zone where the client is physically
situated.

Either way, the most critical aspects of the whole exercise are that:

1. The time zone for both the 'server' and 'client' machines are
set correctly,

and

2. The date and time for both the 'server' and 'client' machines are
regularly corrected using a reliable source.

The key to solving the 'problem' is to forget about time zones per se, and
to think in terms of a common point of comparison and the differences from
that point.

In terms of date/time we, happily, have the concept of Universal Time
Coordinated (UTC) which provides a common reference point for expressing
date/time anywhere in the world. For those who haven't caught up yet, UTC
used to be known as Greenwhich Mean Time (GMT).

We know that your 'client' machine is physically situated somewhere within
the Eastern Time (US & Canada) time zone which is 5 hours behing UTC. We
will take you literally and assume that your 'server' machine is
physically located 'halfway around the world', in a time zone that is 5
hours ahead of UTC.

As long as both machines are configured correctly, they will be aware of
daylight saving factors relating to their respective time zones and,
therefore daylight saving adjustments will be applied to any date/time
calculations automatically.

For 'one end' to be able to express date/time factors in terms of the
'other end' then one end has to:

1. Know in advance where the other end is, in relation to UTC,

or

2. Be told as required what the date/time is at the other end, in terms
of UTC.

Knowing in advance where the other end is, in relation to UTC, is not
really practical for an ASP.NET application because it would need to know
in advance the location of every machine that could ever submit a request
ot it.

So that leaves us with communicating the necessary information as and when
required.

The DateTime structure nicely presents us with properties and methods for
dealing with values expressed in terms of UTC.

To 'capture' the local date and time as UTC we use:

Dim _utc As DateTime = DateTime.UtcNow

MySendUTCToOtherEnd(_utc)

To convert a UTC date and time to local we use:

Dim _remoteutc as DateTime = MyGetUTCFromOtherEnd()

Dim _local As DateTime = _remoteutc.ToLocalTime

_local now contains a value that represents the date and time from the
remote machine expressed in terms of the time zone where the local machine
is physically located.

To illustrate with an example:

Client machine is UTC - 5 hours
Server machine is UTC + 5 hours

Client local date/time = February 18, 7:00 PM
Server local date/time = February 19, 5:00 AM

UTC value passed from client = February 19, 0:00 AM

_local as calculated by server = February 19, 5:00 AM

and, in reverse:

Client machine is UTC - 5 hours
Server machine is UTC + 5 hours

Server local date/time = February 19, 5:00 AM
Client local date/time = February 18, 7:00 PM

UTC value passed from server = February 19, 0:00 AM

_local as calculated by client = February 18, 7:00 PM


"Nathan Sokalski" <njsokalski@xxxxxxxxxxx> wrote in message
news:OZBJ1uFNGHA.2300@xxxxxxxxxxxxxxxxxxxxxxx
I asked a question about a week ago about how to get my local time, since
my application is running on a server halfway around the world. I have
determined that my code would look something like this:

Dim servertime As Date = Date.Now

Dim utctime As Date = servertime.ToUniversalTime()

Dim localtime As Date


I know that the last step would be to adjust the utctime value by the
appropriate amount using code such as utctime.AddHours(-5), but I am
looking for a way to get this value by supplying the timezone rather than
an offset (in other words, I am looking for a function that returns
either a System.TimeSpan or Integer when I enter the timezone) so that I
can do something such as

utctime.AddHours(GetTZOffset(TimeZones.EST))

Is there a function that does this, or any way to get the offset by
submitting the timezone? Thanks.
--
Nathan Sokalski
njsokalski@xxxxxxxxxxx
http://www.nathansokalski.com/





.

Relevant Pages

  • Re: Converting the time from one timezone to another
    ... Carry out some calculation at the server using a date/time pasesed ... from the client that represents the a point in time at the client ... For those who haven't caught up yet, UTC ...
    (microsoft.public.dotnet.framework)
  • Re: Converting the time from one timezone to another
    ... Just have your client side code calculate the utc offset and pass the result ... are talking about an ASP.NET application running on a web server halfway ... expressed in terms of the time zone where the server is physically ...
    (microsoft.public.dotnet.framework)
  • Re: [Fwd: Re: Access to UTC time with servers running in local time - a server-only answer!]
    ... -- @Create UTC Stored Procedure - to return UTC time. ... the seconds component of local time and UTC is always the same in ... the number of minutes since the epoch. ... than server local time value). ...
    (comp.databases.informix)
  • Re: DateTime fundamentally broken
    ... No, it is returning the current date/time OF the server, converted to UTC, ... DateTime.UtcNow method, the date/time was in terms of UTC. ... > Is it not returning the UTC time at the client? ...
    (microsoft.public.dotnet.framework.webservices)
  • Re: hwclock problem with leapseconds - posix?
    ... Find a real news server. ... see setting the system to TAI - but all other tasks would likely be ... served better by using UTC. ... My concern as a network admin is to have ...
    (comp.os.linux.setup)