Develop Reference

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

Converting this string format to a valid DateTime?

The string in question: "2003:12:14 12:01:44" (yyyy:MM:dd hh:mm:ss)
How would I be able to convert this to a valid datetime in C#? I tried Convert.ToDateTime(str), but to no avail.

Use the right DateTime format and supply DateTime.ParseExact with that format. Note that since your time doesn't show AM or PM, it may be safer to assume that it uses 24-Hr format (use capital HH) than 12-Hr AM PM (not hh) format. The following code should work:
string format = "yyyy:MM:dd HH:mm:ss"; //note: use HH not hh
var result = DateTime.ParseExact("2003:12:14 12:01:44", format, CultureInfo.InvariantCulture);
Check more on the available DateTime formats here (standard) and here (custom).

Convert.ToDateTime try to parse your string as a standard date and time format of your CurrentCulture settings. Looks like this string is not a standard format.
You can use DateTime.ParseExact for specify custom format.
var dt = DateTime.ParseExact("2003:12:14 12:01:44",
"yyyy:MM:dd hh:mm:ss",
CultureInfo.InvariantCulture);

How to set/know DateTime class date format interpretion?

I have a particular loop where DateTime instances are to be generated. My problem is on how does the class interpret the input string.
The incoming input strings are of the format MM/dd/yyyy.
Suppose I have "1/17/2014", DateTime would interpret this as MM/dd/yyyy.
But if I have "6/5/2014", how will I be sure that DateTime will parse this with the format MM/dd/yyyy and not dd/MM/yyyy?
EDIT: Inputs may come with the month and/or day in one- or two-digit format.

Because the dates could come in either MM/dd/yyyy or M/d/yyyy then the overload that takes a string[] is the most appropriate:
var dt = DateTime.ParseExact(input,
new[] { "M/d/yyyy", "MM/dd/yyyy" },
CultureInfo.InvariantCulture,
DateTimeStyles.None);
Now, regardless of the zero-padding it will work as expected.

Use the ParseExact function to specify the format :
DateTime d = DateTime.ParseExact("6/5/2014", "M/d/yyyy", CultureInfo.InvariantCulture);
If your input are in MM/dd/yyyy format, you will get 06/05/2014 instead of 6/5/2014. You will then have to use :
DateTime d = DateTime.ParseExact("06/05/2014", "MM/dd/yyyy", CultureInfo.InvariantCulture);
Be sure of your input format if you don't want to have an exception.

take a look at DateTime.ParseExact, which will allow you to specifically match the string

Getting an error while converting string to DateTime

I am trying to convert a string value into DateTime. It gives me an error as, specified string is not in correct format.
Here is the code,
DateTime myDate = DateTime.ParseExact("07-09-2013 01:14:14:1414", "yyyy-MM-dd HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture);
string strDate = "07/09/2013 01:04:02:4";
Convert.ToDateTime(strDate);
DateTime dt = DateTime.Parse(strDate);
Please help in converting the same.
Thanks

Your format seems to be incorrect. Should be:
"dd-MM-yyyy HH:mm:ss:ffff"
Update. If number of digits representing fractions of a second varies, than the best bet is
"dd-MM-yyyy HH:mm:ss:FFFFFFF"
Refer to MSDN for other options for custom time and date formats.

Try in your page_load event:
Thread.CurrentThread.CurrentUICulture = New System.Globalization.CultureInfo("tr-TR")
Thread.CurrentThread.CurrentCulture = New System.Globalization.CultureInfo("tr-TR")

First, you mixed you years place
07-09-2013 is dd-MM-yyyy format
second, you need a :ffff after seconds
So the final line should be
DateTime myDate = DateTime.ParseExact("2013-07-09 01:14:14:1414", "yyyy-MM-dd HH:mm:ss:ffff", System.Globalization.CultureInfo.InvariantCulture);

Your format isn't correct:
"07-09-2013 01:14:14:1414"
"yyyy-MM-dd HH:mm:ss"
Atleast your date is the other way around, and the milliseconds is not specified.
Correct you format according to this: http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx
For the downvoter:
The correct format is specified by Andrei: "dd-MM-yyyy HH:mm:ss:ffff"

First of all, you should change your date format to dd-MM-yyyy because it fits with your date format.
Second of all, for miliseconds part, you can use . instead of :
DateTime myDate = DateTime.ParseExact("07-09-2013 01:14:14.1414", "dd-MM-yyyy HH:mm:ss.ffff", System.Globalization.CultureInfo.InvariantCulture);
string strDate = "07/09/2013 01:04:02.4";
Convert.ToDateTime(strDate);
DateTime dt = DateTime.Parse(strDate);
Here a DEMO.
For more information, check Custom Date and Time Format Strings

Issue in Converting Date Time c#

I am facing an issue when converting the datetime
var date = DateTime.Now;
txtdate.Text = date.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);
//I need to pass it later to as a DateTime variable. When i re-convert it gives me an error)
DateTime dtReconvert =Convert.toDateTime(txtdate.Text); //Error String was not recognized as a valid DateTim
When i set the datetime to something like "01/01/2013"
and convert it to Date Time it not giving me any error.

Use DateTime.ParseExact with the format "dd/MM/yyyy"
DateTime dtObject = DateTime.ParseExact(txtdate.Text,
"dd/MM/yyyy",
CultureInfo.InvariantCulture);

try this
DateTime.ParseExact(txtdate.Text, "MM/dd/yyyy", System.Globalization.CultureInfo.InvariantCulture)
or
Convert.ToDateTime(txtdate.Text, CultureInfo.InvariantCulture)
Microsoft have adopted MM/dd/yyyy as a culture-agnostic format, it's an ambiguous format which isn't something that I would want to build a large system on.