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Date conversion

I need help to convert current date to "Tue Nov 4 00:00:00 UTC+0530 2014" date format
using C#.
Say I have date like : DateTime dt = DateTime.Now;
Now, how can I convert it in mentioned format.

DateTime.ToString(string) allows you to specify a format for your date. You can construct a custom format using Custom Date and Time Format Strings.

I feel like taking risk to answer your question but anyway..
A DateTime doesn't have any implicit format. It just have date and time values etc.. That's why it is not possible to have any format. But string representations of them can have a format. Formatting a DateTime is easy, just need to use DateTime.ToString() method with a specific culture. (In your case looks like InvariantCulture is a good candidate)
DateTime dt = DateTime.Now;
dt.ToString("ddd MMM d HH:mm:ss 'UTC+0530' yyyy", CultureInfo.InvariantCulture);
returns
Tue Nov 4 14:20:36 UTC+0530 2014
AFAIK, time zone abbreviations are not standardized and that's why there is way to parse them besides literal string delimiter. Also since a DateTime doesn't keep offset value, you need also parse it as a literal string delimiter
If you would want to +05:30 instead +0530 as a result, "zzz" custom format specifier would be a nice choice since it gets + or - sign, hours and minutes part offset of local operating system's time zone from UTC.

Based upon your suggestions, I build this code
DateTimeOffset localTime = DateTimeOffset.Now;
string.Format("{0:ddd MMM d HH:mm:ss} UTC+{1} {0:yyyy}", localTime, localTime.Offset.ToString("hhmm"));
and its generating correct format:
"Tue Nov 4 18:25:48 UTC+0530 2014"

Read non regular time format from excel in C#

I am trying to read non regular time format from excel in C#, the time value in excel is as "29-Aug-01 11.23.00.000000000 PM", and in excel the cells format is 'regular' not 'time'.
Now I need read the time in excel then assign the time into calendar time in asp.net/c#, how can I let the program understand the time format?
Big thx!
my code does not work
DateTime expTime = DateTime.ParseExact(strDate, "dd-MMM-yy hh.mm.ss.fffffffff tt", System.Globalization.CultureInfo.CurrentUICulture.DateTimeFormat);

I have similar solution, but more accur.
string s = "29-Aug-01 11.23.00.000000000 AM";
DateTimeOffset myDate = DateTimeOffset.ParseExact(
s,
"dd-MMM-yy hh.mm.ss.fffffff00 tt",
System.Globalization.CultureInfo.InvariantCulture);
EDIT:
You can't use more then 7 'f' chars.

The original format string fails because the DateTime type can't represent nanoseconds. The following format string will work:
var expTime = DateTime.ParseExact(strDate, "dd-MMM-yy hh.mm.ss.fffffff00 tt",
CultureInfo.InvariantCulture);
This works because the 00 characters are interpreted as literals and ignored during parsing.
Note that I'm passing CultureInfo.InvariantCulture instead of the system's UI Culture. This ensures that the English month abbreviations will be used even if the user's UI Culture is set to another language. Otherwise, DateTime.ParseExact will try to parse the date string using the user's language month abbreviations

Parse Date Time from US Time zone to Datetime.

How to parse below date time string?
2014-01-17T09:59:24.000Z
I tried below code but its, not working.
DateTime.ParseExact("2014-01-17T09:59:24.000Z", "ddd MMM dd HH:mm:ss %zzzz yyyy", CultureInfo.InvariantCulture);

With a string like "2014-01-17T09:59:24.000Z"
You can just use DateTime.Parse("2014-01-17T09:59:24.000Z")
From The Documentation:
The string to be parsed can take any of the following forms:
A string that includes time zone information and conforms to ISO 8601. In the following examples, the first string designates Coordinated Universal Time (UTC), and the second string designates the time in a time zone that's seven hours earlier than UTC:
2008-11-01T19:35:00.0000000Z
2008-11-01T19:35:00.0000000-07:00

From DateTime.ParseExact
Converts the specified string representation of a date and time to its
DateTime equivalent using the specified format and culture-specific
format information. The format of the string representation must match
the specified format exactly.
Clearly your string representation and format is not the same.
You can use it like;
var date = DateTime.ParseExact("2014-01-17T09:59:24.000Z",
"yyyy-MM-dd'T'HH:mm:ss.fff'Z'",
CultureInfo.InvariantCulture);
Console.WriteLine(date);
Output will be;
1/17/2014 9:59:24 AM
Here a demonstration.
For more information, take a look at;
Custom Date and Time Format Strings

The value you have, 2014-01-17T09:59:24.000Z is an ISO8601/RFC3339 formatted timestamp. The Z at the end is significant, which means that it represents UTC.
You have two options to correctly parse it:
You could parse it to a DateTime that has DateTimeKind.Utc for it's .Kind property:
DateTime dt = DateTime.ParseExact("2014-01-17T09:59:24.000Z",
"yyyy-MM-dd'T'HH:mm:ss.fffK",
CultureInfo.InvariantCulture,
DateTimeStyles.RoundtripKind);
Or, you could parse it to a DateTimeOffset, where UTC will correspond to an offset of zero:
DateTimeOffset dt = DateTimeOffset.ParseExact("2014-01-17T09:59:24.000Z",
"yyyy-MM-dd'T'HH:mm:ss.fffK",
CultureInfo.InvariantCulture);
Some of the other answers here are close, but are forgetting to actually consider the Z in your string, using the K specifier and the DateTimeStyles.RoundtripKind parameter. These are important, for without them you will likely end up with a resulting DateTime that has DateTimeKind.Unspecified, which could get treated as local time in certain time zone conversion functions. If you use either of the options I gave you, then the meaning of the Z is preserved.

Trying to parse a DateTime in C#

I am trying to parse a DateTime in C# and have the following lines of code:
string dt =Convert.ToString( DateTime.FromFileTime(e8.sts[counter8].TimeStamp));
string format = "dd-MM-yyyy HH:mm:ss";
DateTime dateTime = DateTime.ParseExact(dt, format,CultureInfo.InvariantCulture);
When I debug dt is coming in as 05/18/2011 09:25:17 AM but I get an expection saying:
String was not recognized as a valid
DateTime.

Starting off, you have no need for the conversion.
DateTime.FromFileTime(e8.sts[counter8].TimeStamp) returns a DateTime already...
Even so, with the string you have provided, DateTime.Parse(str) will take care of you.
If you end up storing this value in a text file, and really are dead-set on using a custom format string to parse it (which you don't need to):
The format you have:
Day/Month/Year 24-hour:minute:second
But looking at your input date:
05/18/2011 09:25:17 AM
You want:
Month/Day/Year 12-hour:minutes:seconds AM/PM
The format for what you want is:
MM/dd/yyyy hh:mm:ss tt

Isn't this expected? Date 05/18/2011 09:25:17 AM doesn't match your format string dd-MM-yyyy HH:mm:ss. Your date is in format MM/dd/yyyy HH:mm:ss tt.
Try this:
DateTime dateTime = DateTime.Parse("05/18/2011 09:25:17 AM");

I don't see any reason for the conversion. Just use:
DateTime.FromFileTime(e8.sts[counter8].TimeStamp)

Your DateTime is coming in as MM-dd-yyyy but you are trying to parse it as dd-MM-yyyy
Change your format string to "MM-dd-yyyy HH:mm:ss tt"
You can tell this as dt, using your current format string, is trying to be parsed as the 5th day (dd) of the 18th month (MM) of 2011 (yyyy)...
EDIT:
Sorry, I completely missed the AM/PM designator, you need the tt part of the format string. This will handle the AM/PM part of the string
EDIT 2:
As per your most recent comment, you want to convert it into MM-dd-yyyy HH:mm:ss string, the all you need to do is:
var outputString = DateTime.FromFileTime(e8.sts[counter8].TimeStamp).ToString("MM-dd-yyyy HH:mm:ss");
You already have the TimeStamp in a val;id .NET DateTime object, so all you need to do is perform a .ToString() with the required time format.

DateTime parsed = DateTime.ParseExact(dt,"MM/dd/yyyy HH:mm:ss tt",CultureInfo.InvariantCulture);

s many of the others have explained here, the format needs to be changed. However even when I tried the formats they have suggested, I still received the same error that you did. Eventually I hit upon the right format to get successful results.
The format should be:
string format = "MM/dd/yyyy HH:mm:ss tt";
because you are specifying time pattern such as AM. If the month is given as single digit, eg: 5, then MM should be replaced with M. I used slash instead of hypen between the dates because that's how the original date had been given.

Convert.DateTime

What Convert.DateTime will convert the date 7/25/2010 12:00:00 it's current format is(MM/dd/yyyy HH:mm:ss)?
When I convert this string format to date time I am getting the error "string was not recognized as valid DateTime"

None. Dates are not stored internally as a certain format.
If you want to parse a string into a date, use DateTime.ParseExact or DateTime.TryParseExact (the former will throw an exception if the conversion fails, the second uses an out parameter):
DateTime myDate = DateTime.ParseExact("7/25/2010 12:00:00",
"MM/dd/yyyy HH:mm:ss",
CultureInfo.InvariantCulture);
If you want to display a certain format, use ToString with the format string.
So, if you have a date object that represents midday of the 25th of July 2010 (doesn't matter how it is represented internally) and you want to format it with the format string "MM/dd/yyyy HH:mm:ss" you do the following:
string formattedDate = myDate.ToString("MM/dd/yyyy HH:mm:ss");

If you need to use Convert.DateTime, I'll assume you're working with a string you want to convert to a date. So you might try this:
DateTime date = Convert.DateTime("7/25/2010 12:00:00 am");
string formattedDateString = date.ToString("MM/dd/yyyy HH:mm:ss")
I'm making no assumptions as to why you'd want to do this, except that, well, you have your reasons.

DateTime.TryParse() or DateTime.Parse() will do the trick.
Edit: This is assuming that you are going from a string to a DateTime object.
Edit2: I just tested this with your input string, and I receive no error with DateTime.Parse