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change format of datetime.now

I want to get the last seen of user and save it to my sql database in mvc5 . I got the last seen in controller with code like this:
users.userlast=DateTime.Now;
and saved to my database in this format "2015-08-06 12:12:13.443". I want to get datetime only format day,month,year, hour and minute.
I can't use something like this,
var dateTime = DateTime.ParseExact("12/02/21 10:56:09", "yy/MM/dd HH:mm", CultureInfo.InvariantCulture);
var text = dateTime.ToString("MMM. dd, yyyy HH:mm");
It did not work because my last seen column is a datetime type not string. What should i do?
Thanks.
Edit:
Like whatsup App., i want to see only hour and minute, not seconds as last seen.

You say that you are storing as a datetime type, in which case the you shouldn't need to convert a string to a DateTime. In fact you shouldn't need to do any parsing.
When you query the database you should get a DateTime, on which you can call the ToString() you want.

to get datetime in format day, month, year, hour and minute only (without seconds, milliseconds), create a new DateTime value before save:
var dt = DateTime.Now;
users.userlast = dt.Date.AddHours(dt.Hour).AddMinutes(dt.Minute);

You don't have to worry about the format you save in the database. When you want to represent it in your specific format you can ToString it accordingly.
I want to get datetime only format day,month,year, hour and minute.
string text = dateTime.ToString("yyyy-MM-dd HH:mm",
CultureInfo.InvariantCulture);
CultureInfo.InvariantCulture is to use your specified culture regardless of the user's current culture.

You can use InvariantCulture because your user must be in a culture that uses a dot instead of a colon:
DateTime.ToString("yyyy-MM-dd HH:mm", CultureInfo.InvariantCulture);

Just do like that
var formattedDateTime = yourLastSeenDateTime.ToString("MMM. dd, yyyy HH:mm", CultureInfo.InvariantCulture);
EDIT: Try this as you mentioned in comments
DateTime dbDate = yourLastSeenDateTime;
DateTime newDateTime = new DateTime(dbDate.Year, dbDate.Month, dbDate.Day, dbDate.Hour, dbDate.Minute, 0);

Convert string into mm/dd/yyyy format

I have following strings in different formats:
16/05/2014
21-Jun-2014
2014-05-16
16-05-2014
5/19/2014
14 May 2014
I need to convert all the above strings into mm/dd/yyyy format in c#.
I have tried used DateTime.ParseExact as DateTime dt = DateTime.ParseExact("16-05-2014", "mm/dd/yyyy hh:mm:ss tt", CultureInfo.InvariantCulture) in C# but i am getting the exception as "String was not recognized as a valid DateTime".
I have also tried to use to Convert.ToDateTime() but it is also not working.
Is there any method or function that we can write/available in C# that would convert the above string formats into a single date format i.e into "mm/dd/yyyy" format ??
Any help on this would be greatly appreciated.

It fails on the very first term of your format string, which is telling the function to treat the "16" as minutes and to look for hours, minutes, and seconds that don't exist in the input.
You have several different date formats, and so need the ParseExact() overload that accepts several different format strings:
string[] formats= {"dd/MM/yyyy", "dd-MMM-yyyy", "yyyy-MM-dd",
"dd-MM-yyyy", "M/d/yyyy", "dd MMM yyyy"};
string converted = DateTime.ParseExact("16-05-2014", formats, CultureInfo.InvariantCulture, DateTimeStyles.None).ToString("MM/dd/yyyy");
Also remember that lower case "m"s are for minutes. If you want months, you need an upper case "M". Full documentation on format strings is here:
http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx
Finally, I suspect you are getting ahead of yourself on formatting the output as a string. Keep these values as DateTime objects for as long as possible, and only format to a string at the last possible moment before showing them to the user. If you really do want a string, at least stick with the ISO 8601 standard format.

Your main problem is that your format string is wrong. A small m is for minute, a big M is for month.
Try to pass all your formats in an array. For example like this
DateTime.ParseExact("16-05-2014",
new[] {"dd/MM/yyyy", "dd-MMM-yyyy", "yyyy-MM-dd",
"dd-MM-yyyy", "M/d/yyyy", "dd MMM yyyy"},
CultureInfo.InvariantCulture, DateTimeStyles.None);
With this you can parse all your formats at once.
For more information about the format settings, see the official docs.

Few things:
Your input date 16/05/2014 doesn't match your format Month/Day/Year - how can there be a 16th month?
Secondly, you're using mm which represents Minutes, not Months. You should use MM.
Finally, your sample string 16-05-2014 doesn't match the format provided, you've used hyphens - instead of forward slashes /
Supply a collection of different formats matching your input:
string[] formats = new [] { "MM/dd/yyyy", "dd-MMM-yyyy",
"yyyy-MM-dd", "dd-MM-yyyy", "dd MMM yyyy" };
DateTime dt = DateTime.ParseExact("05-16-2014", formats, CultureInfo.InvariantCulture, DateTimeStyles.None);

You might find the following method useful to accept whatever date format you want and convert it to DateTime:
public DateTime? DTNullable(string DateTimestring, string CurrDateTimeFormat)
{
if (string.IsNullOrEmpty(DateTimestring)) return null;
else
{
DateTime datetimeNotNull;
DateTime.TryParseExact(DateTimestring, CurrDateTimeFormat, null, System.Globalization.DateTimeStyles.None, out datetimeNotNull);
return datetimeNotNull;
}
}
Pass in your desired string to be converted to DateTime along with it's current date time format and this would return you a nullable DateTime. If you're certain that whatever string you're passing in won't be null then you can remove that bit. The reason for it being there is that you can't convert a null to DateTime. In my case I couldn't be certain if it would be or not so I needed the ability to capture nulls as well.
You can use it like this:
DateTime? MyDateTime = DTNullable(MyStartDate, "dd/MM/yyyy");
If you wanted you could alter the method to accept an array of strings and simply iterate through each and return them all in a list if they were of the same format.
As others have pointed out, months are MM not mm (minutes).

On a DateTime object you can call .ToString("MM/dd/yyyy"). Given the strings you have, you can first create new DateTime objects for each string and then call .ToString("MM/dd/yyyy"). For example:
var dateAsMmDdYyyy = DateTime.Now.ToString("MM/dd/yyyy");

DateTime.Parse - changes format

I'll try to illustrate an example:
var dateNow = DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss");
produces: 10/01/2014 21:50:34
var dateNowParse = DateTime.Parse(DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss"));
produces: 10/01/2014 9:50:34 PM
QUESTION:
How to parse the date, and keep formatting like: dd/MM/yyyy HH:mm:ss, with an 24 hour format, without any PM
Thank you!
Update 1
Sorry maybe my question wasn't so clear, i'll try to explain the real situation below.
Please do not focus on real meaning of DateTime.Now, suppose we have a string variable in the format of 10/01/2014 21:50:34, and then I try to parse it, and store the result in another variable. What I am willing to achieve is to keep the result in a DateTime variable which has the exact formatting 10/01/2014 21:50:34.
Now here is a snippet:
var stringDate = "10/01/2014 22:50:30";
DateTime parsedDate = DateTime.Parse(stringDate, CultureInfo.InvariantCulture);
//parsedDate result is: 10/01/2014 10:50:30 PM
What is frustrating me is:
In the stringDate the 22:50 hour says that the string is formatted to the 24 hour clock. (the 12 clock format uses hours counter up to 12)
If I used 22:50, Isn't logically that the output should'nt use any AM PM and 12 hour format?

How to parse the date, and keep formatting
You need to keep the format alongside the DateTime if you want to. A DateTime does not have any concept of being in a particular format. The value of the DateTime returned by Parse isn't "10/01/2014 9:50:34 PM" - it's that particular date and time, but not a string representation.
You could have a type which maintains the two together - or if you always want to format in the same way, just specify that format explicitly when you format, without keeping it as data with the DateTime value.
Personally I would try to stick to DateTime.ParseExact where feasible, as I find it easier to predict what it will do - but it does depend on your input. If it's input with a particular format that you're expecting, ParseExact really is the way forward, potentially with the invariant culture to avoid any cultural differences.

I would store the date now as a date
DateTime dateNow = DateTime.Now;
then when you need to display it with that formatting
String strNow = dateNow.ToString("dd/MM/yyyy HH:mm:ss");
If you have a date coming in with a format say in a String variable strNow and want to put it in the DateTime I would make sure to catch format exceptions
DateTime dateNow;
try {
dateNow = DateTime.ParseExact(strNow, "dd/MM/yyyy HH:mm:ss", CultureInfo.InvariantCulture);
}
catch (FormatException) {
//Log something or set a default date.
}

DateTime.ParseExact(DateTime, Format, DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AllowLeadingWhite | DateTimeStyles.AllowTrailingWhite);
for example:
DateTime.ParseExact(strNow, "dd/MM/yyyy HH:mm:ss", DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AllowLeadingWhite | DateTimeStyles.AllowTrailingWhite);

how to convert time in string format into date time format using C#

i have textbox that accepts time format like this 12:40 PM but would like to convert it into time format like this 12:40:00 basically without the PM or AM. Here is what i have so far:
string StartTime = ((TextBox)TestDV.FindControl("txtBST")).Text.ToString();
thanks

One option would be to parse into a DateTime and then back to a string:
string s = "12:40 PM";
DateTime dt = DateTime.Parse(s);
string s2 = dt.ToString("HH:mm:ss"); // 12:40:00
Be aware, however, that most operations work better with a DateTime versus a string representation of a DateTime.

First you should parse it to a DateTime, then format it. It sounds like your input format is something like hh:mm tt and your output format is HH:mm:ss. So, you'd have:
string input = "12:40 PM"
DateTime dateTime = DateTime.ParseExact(input, "hh:mm tt",
CultureInfo.InvariantCulture);
string output = dateTime.ToString("HH:mm:ss", CultureInfo.InvariantCulture);
Note that:
I've used DateTime.ParseExact which will throw an exception if the parsing fails; you may want to use DateTime.TryParseExact (it depends on your situation)
I've used the invariant culture for both operations here. I don't know whether or not that's correct for your scenario.
I've used hh:mm, but you might want h:mm... would you expect "1 PM" or "01 PM"?
You don't parse seconds, so that part will always be 0... is that okay?

Since you are bringing it in as a string this is actually kind of easy.
string StartTime = ((TextBox)TestDV.FindControl("txtBST")).Text.ToString();
DateTime dt = new DateTime();
try { dt = Convert.ToDateTime(StartTime); }
catch(FormatException) { dt = Convert.ToDateTime("12:00 AM"); }
StartTime = dt.ToString("HH:mm");
So you bring in your string, and convert it to a date. if the input is not a valid date, this will default it to 00:00. Either way, it gives you a string and a DateTime object to work with depending on what else you need to do. Both represent the same value, but the string will be in 24-Hour format.
Cheers!!

How to Convert Date Object with Format "MM/dd/yy hh:mm:ss tt" to DateObject with Format "dd/MM/yy

I have googled alot and tried lot of solutions but nothing is working for me.For Ex i Have tried below :
public static DateTime ParseDateToSystemFormat(DateTime date)
{
IFormatProvider culture = new CultureInfo("en-GB", true);
DateTime dt = DateTime.ParseExact(date.ToString("dd/MM/yyyy"),
"dd/MM/yyyy",
culture,DateTimeStyles.NoCurrentDateDefault);
return Convert.ToDateTime(dt,culture);
}
If anyone have solved this please let me know.

Date objects do not have formatting associated to them - you only use formatting for display.
When it is time to display the DateTime object, use either custom or standard format strings to format the display to your liking.
What you are doing here:
DateTime dt = DateTime.ParseExact(date.ToString("dd/MM/yyyy"),
"dd/MM/yyyy",
culture,DateTimeStyles.NoCurrentDateDefault);
Is rather strange - you are getting a specific string representation of your DateTime - date.ToString("dd/MM/yyyy"), then parsing that string back to a DateTime object. A bit of a long way to say DateTime dt = date;, with clearing out the hours/minutes/seconds data.
If you simply want the date portion of a DateTime, use the Date property. It produces:
A new object with the same date as this instance, and the time value set to 12:00:00 midnight (00:00:00).

The internal representation of a DateTime is always the same. There is no formatting attached to a DateTime object.
If it is only a display problem, then convert the DateTime to a string and display that string. You already know how to do it: Using ToString and specifying the format you want to have.