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Change DateTime Format {"MM/dd/yyyy"} to {"dd/MM/yyyy"} and time should remain same in Unity

I want to change DateTime now to the Format {"MM/dd/yyyy"} using this code.
string.Format("{0:MM:dd:yyyy}", DateTime.Now)
and saving it.
after getting saved string I get DateTime in format {"MM/dd/yyyy"} . Now I want to convert it in another format so I can Parse to DateTime. when I try to parse MM/dd/yyyy to DateTime got an error
"FormatException: String was not recognized as a valid DateTime."
Thanks in Advance.

You can rather use DateTime.ParseExact which allows you to specify the exact date format you are expeting the input to have.
For example
var now = DateTime.Now;
Debug.Log(now.ToString("dd.MM.yyyy"));
var example1 = now.ToString("MM/dd/yyyy");
Debug.Log(example1);
var readTime1 = DateTime.ParseExact(example1, "MM/dd/yyyy", CultureInfo.InvariantCulture);
Debug.Log(readTime1.ToString("dd.MM.yyyy"));
var example2 = now.ToString("dd/MM/yyyy");
Debug.Log(example2);
var readTime2 = DateTime.ParseExact(example2, "dd/MM/yyyy", CultureInfo.InvariantCulture);
Debug.Log(readTime2.ToString("dd.MM.yyyy"));
See Fiddle

The format is only relevant for display
If you save it in a C# DateTime variable, there is no "format" when saving it, this DateTime is a struct data type which is universal and not bound to any specific format
If you want to use a specific format for parsing, you can use:
// Parse date and time with custom specifier.
CultureInfo provider = CultureInfo.InvariantCulture;
dateString = "Sun 15 Jun 2008 8:30 AM -06:00";
format = "ddd dd MMM yyyy h:mm tt zzz";
DateTime myDate = DateTime.ParseExact(dateString, format, provider);
You can use CultureInfo to optimize your format for you needs
If there is a need to save it as "MM/dd/yyyy", your should save it as string
best regards

Convert date string to DateTime format

I have the date string like 03/10/1999 where the format is dd/MM/yyyy (pt-BR format).
And I need to convert this date for a SQL-like format yyyy-MM-dd HH:mm:ss.fff.
I tried to use Parse and ParseExact functions, but no success so far. I will let my results below...
Using Parse
var BrazilianDate = "03/10/1999";
var Parse = DateTime.Parse(BrazilianDate, new CultureInfo("pt-BR"));
Console.WriteLine("Parsed date: " + Parse);
Output: Parsed date: 10/3/1999 12:00:00 AM
No hyphens or milliseconds...
Using ParseExact
var BrazilianDate = "03/10/1999";
var ParseExact = DateTime.ParseExact(BrazilianDate, "yyyy-MM-dd HH:mm:ss.fff", new CultureInfo("pt-BR"));
Console.WriteLine(ParseExact);
output:
Run-time exception (line -1): String was not recognized as a valid
DateTime.
Stack Trace:
[System.FormatException: String was not recognized as a valid
DateTime.] at System.DateTimeParse.ParseExact(String s, String
format, DateTimeFormatInfo dtfi, DateTimeStyles style) at
System.DateTime.ParseExact(String s, String format, IFormatProvider
provider) at Program.Main()

You need to format your output with the correct format string like this:
Console.WriteLine("Parsed date: " + Parse.ToString("yyyy-MM-dd HH:mm:ss.fff"));
//Parsed date: 1999-10-03 00:00:00.000
If you don't specify a format, .NET picks whatever it thinks is the right one (which it often isn't when you're not in the US).
You also need to strictly separate between the DateTime value and its representation in string form. No matter how you format it, the value itself will stay the same.

The format string you use in the parse method represents the format of the input string.
A DateTime does not have a display format, in fact it's a numeric value representing the number of ticks since a specific Epoch.
From official documentation:
Time values are measured in 100-nanosecond units called ticks. A particular date is the number of ticks since 12:00 midnight, January 1, 0001 A.D. (C.E.) in the GregorianCalendar calendar. The number excludes ticks that would be added by leap seconds. For example, a ticks value of 31241376000000000L represents the date Friday, January 01, 0100 12:00:00 midnight.
When parsing strings, I find it's best to either use ParseExact or TryParseExact. To print our the string representation of the DateTime value, use the overload of ToString that takes in a string that represent the format you want to display.
var BrazilianDateString = "03/10/1999";
var DateTimeValue = DateTime.ParseExact(BrazilianDate, "dd/MM/yyyy", CultureInfo.InvariantCulture);
Console.WriteLine(DateTimeValue.ToString("yyyy-MM-dd HH:mm:ss.fff");

This code is working for me:
DateTime dt = new DateTime();
string x = "03/10/1999 22:10:10";
dt = DateTime.Parse(x);
Console.WriteLine(dt.ToShortDateString());
Console.WriteLine(dt.ToShortTimeString());
Console.ReadLine();
Console output:
03/10/1999
22:10
Don't use that CultureInfo, DateTime can understand spanish-brazilian dates on its own

DateTime format conversion mm/dd/yyyy to yyyy/mm/dd

Can someone please let me know how do I convert this datetime format into yyyyMMdd
2/28/2017 12:02:04 AM
At the output I should get 20170228
Any advice on this?

If you already have the DateTime as an object
string formattedDate = date.ToString("yyyyMMdd");
If you need to parse the value first.
string dateValue = "2/28/2017 12:02:04 AM";
string format = "M/d/yyyy hh:mm:ss tt";
DateTime dateTime = DateTime.ParseExact(dateValue, format,
System.Globalization.CultureInfo.InvariantCulture);
For reference you can find a breakdown of the Custom Date and Time Format Strings

You need to specify the format of the date.
If you want it for the current time you can try like this :
string dtime = DateTime.Now.ToString("yyyy/MM/dd");

This is the solution I have come up with for you:
string format = "M/d/yyyy hh:mm:ss tt";
string dateString = "2/28/2017 12:02:04 AM";
CultureInfo provider = CultureInfo.InvariantCulture;
DateTime date = DateTime.ParseExact(dateString, format, provider);
string output = date.ToString("yyyyMMdd");

If you're using C# 6 or later (VS2015), you can format DateTime objects easily by using string interpolation using a custom format string. The custom format string that you're looking for is "yyyyMMdd".
// create your preferred date and time in a new DateTime struct
DateTime yourDateTime = new DateTime(2017, 2, 28, 0, 2, 4);
// format yourDateTime as a string
string yourFormattedDateTime = $"{yourDateTime:yyyyMMdd}";
You can read more about interpolated strings at https://msdn.microsoft.com/en-us/library/dn961160.aspx, and, as previously mentioned by #Adam Carr, you can find more information on custom date and time format strings at https://msdn.microsoft.com/en-us/library/8kb3ddd4(v=vs.110).aspx

string was not recognized as a valid datetime while Converting Date from Hijri to Gregorian date

I am Trying to Convert Hijri Date into Gregorian Date I was following this article and My Code is as follows :
var cultureInfo = CultureInfo.CreateSpecificCulture("ar-sa");
string date = "19/12/36 12:00:00 ص";
Getting
string was not recognized as a valid datetime
error in below line
DateTime tempDate = DateTime.ParseExact(date, "dd/MM/yyyy", cultureInfo.DateTimeFormat, DateTimeStyles.AllowInnerWhite);
lblDate.Text = tempDate.ToString("dd/MM/yyyy");
I am getting string was not recognized as a valid datetime. Please can somebody tell me whats wrong with this code?

I think I'm on the right way but.. Let's try something at least.
First of all, DateTime values are always in the Gregorian calendar, basically. There's no such thing as "A DateTime in a UmAlQuraCalendar calendar" - which is used by ar-sa culture - you have to use the UmAlQuraCalendar to interpret a DateTime in a particular way.
Second, when you use DateTime.ParseExact for parsing your string, your string and format does match exactly based on culture you use. Since ص
character seems AMDesignator of ar-sa culture, you should provide tt specifier with your time part as well.
string s = "19/12/36 12:00:00 ص";
DateTime dt;
if(DateTime.TryParseExact(s, "dd/MM/yy hh:mm:ss tt", CultureInfo.GetCultureInfo("ar-sa"),
DateTimeStyles.None, out dt))
{
Console.WriteLine(dt);
}
Note: Since TwoDigitYearMax is 1451 of UmAlQuraCalendar calendar, your 36 will be parsed as 1436 with yy format specifier.
This perfectly parse your question but WAIT! What will be the result? Here it is.
02/10/2015 00:00:00
Why? As I said in the top, you have to use the UmAlQuraCalendar to interpret this DateTime instance.
UmAlQuraCalendar ul = new UmAlQuraCalendar();
Console.WriteLine(ul.GetYear(dt)); // 1436
Console.WriteLine(ul.GetMonth(dt)); // 12
Console.WriteLine(ul.GetDayOfMonth(dt)); // 19

How to convert dd/mm to Mysql Datetime format in c#

I have a date string with dd/mm format like 06/03.Now i have to store this string into mysql table column with DATETIME format.
I am getting the problem as How can i add the current year generically because i don't want to hard code it.Subsequently how will i convert it into MySql DATETIME format for saving it.
Please help me .

You can use Parse method of DateTime:
DateTime dateTime = DateTime.Parse("06/03");
UPDATE
For your comment:
Also after parsing into DateTime i am getting date correct but time i
dont want to be 12:00:00 AM instead i want it to be 00:00:00.
12:00:00 AM corresponds to 00:00:00 only. You can verify that by getting Hour property which will return 0 and also TimeOfDay will too return 00:00:00.
Even if you try to parse exact date, it also creates the same format.
DateTime dateTime = DateTime.ParseExact("06/03 00:00:00", "dd/MM hh:mm:ss",
CultureInfo.InvariantCulture);
And you don't need conversion from DateTime object to SQL compliant DateTime object. You can pass the .Net object to SQL writer.

Consider the code:
C#
string s = "06/03";
System.DateTime dateNow = Convert.ToDateTime(s);
will give the output as you required
in VB.Net :
Dim s As String = "06/03"
Dim dateNow As Date = CDate(s)
MsgBox(dateNow)

You could do something like
var some_date = "06/03";
var year = DateTime.Now.Year;
var option = some_date+"/"+year;
Or use any of the string formats to bend it to your needs
More on date string format can be found on this MSDN page.
Edit:
If you want zeroes in the time, like your comment said, you can usit Rohit vats answer and do:
DateTime dateTime = DateTime.Parse("06/03");
var s1 = dateTime.ToString("MM/dd/yy 00:00:00");
// Output: 03/06/14 00:00:00
var s2 = dateTime.ToString("MM/dd/yyyy 00:00:00");
// Output: 03/06/2014 00:00:00