Develop Reference

string to dateTime convention changes the format of the string

My code is like this
DateTime dt = new DateTime();
dt= DateTime.ParseExact("14/09/2017", "dd/MM/yyyy", CultureInfo.InvariantCulture);
I am expecting dt to have a format of dd/MM/yyyy but the output I am getting is in MM/dd/yyyy format.
This is the correct out put I am getting 9/14/2017 12:00:00 AM.
Can anyone please point out what I am doing wrong here?

if you expect the format "dd/MM/yyyy" you need to specify it when displaying the DateTime. To do so you can use this overload of the ToString method:
dt.ToString("dd/MM/yyyy");
A DateTime on it's own has no format. Only the string representation of it has one.
EDIT:
Important remark by Tim Schmelter:
/ is a custom format specifier which replaces all occurences with the local date-separator. You either have to esacape them by embedding them within ' or use CultureInfo.InvariantCulture as second parameter. Read this post
That means either use this:
string str_rep = dt.ToString("dd'/'MM'/'yyyy");
or:
string str_rep = dt.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);

Your dt is a DateTime, not a string. Format concept only applies when you get their textual (aka string) representation. What you saw is probably what debbuger/ide shows you as a textual representation.
If you get a specific format of your dt, then you can use .ToString() method with dd/MM/yyyy format and a proper culture like InvariantCulture.
string myFormat = dt.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);
For beginners, it is really important to understand the difference between what is a DateTime and what is their string representation.

If DateTime.ToString() is resulting in an unexpected format, the likely case is that the current culture isn't being set. By default, the date format used is taken from the host machine. However, you can either specify it directly by setting the thread's CurrentCulture for the culture code you need, or you can set it in your application's configuration file. E.g., a web application's web.config can have a globalization section, like so;
<globalization culture="en-GB" uiCulture="en-GB" />
Alternatively, as already specified, you can set the format explicitly via a custom format string .ToString("dd/MM/yyyy").

Convert date in string to DateTime with same format

I have a string that has a date stored in it.
String date = "03-05-2013 00:00:00";
I parsed it to Datetime as follows:
DateTime Start = DateTime.Parse(date);
Start.ToString() gave me "3/5/2013 12:0:00 AM"
I also used:
DateTime Start = DateTime.ParseExact(date,"dd-MM-yyyy HH:mm:ss",CultureInfo.InvariantCulture);
Then, Start.ToString() gave me "3/5/2013 12:0:00 AM", which is the exact same result as the previous one. I need to keep the original formatting. How may I do it? Thanks.

The format you parse with does not dictate how the DateTime is formatted when you convert the date back to a string. When you call ToString on a date it pulls the format from the current culture of the thread your code is executing on (which defaults to the culture of the machine your on).
You can override this by passing the format into ToString() i.e.
Start.ToString("dd-MM-yyyy HH:mm:ss", CultureInfo.InvariantCulture);
See Custom Date and Time Formats.

You need to pass the format in the ToString() call.
Start.ToString("dd-MM-yyy HH:mm:ss");

I need to keep the original formatting.
Then you need to apply the same pattern again when you call ToString:
string formatted = Start.ToString("dd-MM-yyyy HH:mm:ss",
CultureInfo.InvariantCulture);
(Note that you should specify the same culture when formatting as you did when parsing, to avoid things like the time separator from changing.)
Note that for some formats this still might not give the exact original representation - if you're using a format which includes the text for a month, for example, that would match case-insensitively, so input including "MARCH" would be reformatted as "March".
A DateTime value is just a date and time (and a "kind", but that's another story) - it doesn't maintain a textual representation any more than an integer does. It's important to differentiate between the inherent data in a value and a textual representation of that data. Most types which have multiple possible textual representations have no notion of keeping "the original representation" alongside the data.

How to convert MM/dd/yyyy to yyyy/MM/dd in C# using globalization

I have a text box in which a user is supposed to enter a date in MM/dd/yyyy format. This date is stored as yyyy/MM/dd in the database.
I want the user to enter the date in MM/dd/yyyy format and later I want to convert it to yyyy/mm/dd so that I can query the database.
How can I convert the user input date MM/dd/yyyy to yyyy/mm/dd?

If you're certain of the input string's format, use DateTime.ParseExact specifying "MM/dd/yyyy", then return the DateTime using .ToString with the appropriate "yyyy/MM/dd" format string.
There's no need to reference anything in the System.Globalization namespace for this.
That said, your database should be storing dates with a datetime format, rather than a string, in which case the format doesn't matter as your DBMS should do the conversion for you.

You can parse the date and format the result:
string str = Date.Parse(myDate).ToString("yyyy/MM/dd");
Alternatively, if the current culture doesn't support that date format and you've already validated the input:
string items[] = myDate.Split('/');
string str = items[2] + "/" + items[0] + "/" + items[1];

When you said globalization, I assume you want the change to be automatic according to current culture
You can setup culture (at Global.asax.cs I suggest)
System.Threading.Thread.CurrentThread.CurrentCulture = System.Threading.Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo("the culture you want to set"); //
you do not need to touch any datetime thing, it just happened when you output them.

One thing is not the other.
Not sure why you want to insist on the text entered being MM/dd/yyyy, or why you haven't used a date time picker to make sure it is a date.
But at the point you get the content of the textbox as a date, parse it based on globalisation, or a set of acceptable formats. Now it is a date, and assuming it's a date in the database, format is irrelevant until you come to populate the text box, with some content from the DB, inwhich case you use DateTime's ToString method witha globalisation parameter, usually CultureInfo.CurrentCulture, or if you've got away with it CultureInfo.InvariantCulture.
If it's a string in the DB, then this is the least of your problems.
They key point is if you use dates properly, format is only relevant for Parse, and ToString type methods.

i am using
IFormatProvider culture=new CultureInfo("en-GB",true);
sqlcommand cmd=new sqlcommand("query",con);
cmd.Parameters.AddWithValue("#date",DateTime.Parse(txtdate.Text.Trim(),culture,DateTimeStyles.NoCurrentDateDefault).Date);
for this to work the format property must be set to dd/MM/yyyy
and text box read only property must be false

How to make DateTime independent from the current culture?

I cam trying to convert a datetime to string and back, but making it so that it works for all cultures.
I basically have a Textbox (tbDateTime) and a label (lbDateTime). The label tells the user, in which format the software expects the input of tbDateTime. The input of the Textbox will be used for an MySQL command.
Currently it works like this:
lbDateTime.Text = "DD.MM.YYYY hh:mm:ss"; // I live in germany
DateTime date = Convert.ToDateTime(tbDateTime.Text);
String filter = date.ToString("yyyy-MM-dd HH:mm:ss");
Now my question:
Is it possible to determine the format-string for lbDateTime.Text based on the current culture?
Which format does the Convert.ToDateTime function uses?
I hope you can help me. I have actually no pc here to test different cultures, so I'm very afraid that I make something wrong.

Instead of using the Convert.ToDateTime method you can use the DateTime.Parse or DateTime.ParseExact methods. Both allow you to pass a culture that tells how you expect the date to be formatted.
The DateTime.ParseExact method also allows you to specify the format you expect, so you can parse more or less any format with this method.
Edit:
Regarding Convert.ToDateTime. The documentation says that the current culture is used when parsing: http://msdn.microsoft.com/en-us/library/xhz1w05e.aspx
The current culture can be found using the System.Threading.Thread.CurrentThread.CurrentCulture property.
Edit2:
Oh. You may also want to use DateTime.TryParse and DateTime.TryParseExact if you are unsure whether the given format is invalid.
Edit3:
Lots of edits here... I see that you want to determine the culture string that matches the date the user has entered. There is no general solution that is guaranteed to work here. Say for instance that the user has entered the date 01.02.11. There is no way to be certain if this date is in day.month.year or month.day.year or year.month.day and so on.
The best you can do is to have a list of expected input cultures and start with the most likely and try to parse the date using that. If that fails, you can try the second most likely and so on...
But this is really not recommended. Either give the user an expected format, or better, use a date input box that ensures that you receive the selected date in an appropriate format.

The Convert.ToDateTime method will call DateTime.Parse to parse the string, using the current culture (CultureInfo.Current).
You can specify a culture when parsing the string. Example:
DateTime data = DateTime.Parse(tbDateTime.Text, new CultureInfo("en-GB"));
You can use DateTime.ParseExact (or DateTime.TryParseExact) to parse the string using a custom date format. Example:
DateTime data = DateTime.ParseExact(tbDateTime.Text, "dd'.'MM'.'yyyy HH':'mm':'ss", CultureInfo.InvariantCulture);

Another solution :
// Specify the current language (used in the current system you are working on)
CultureInfo currentCulture = CultureInfo.GetCultureInfo(CultureInfo.CurrentCulture.ToString());
// Specify the language that we need
CultureInfo myLanguage = CultureInfo.GetCultureInfo("en-US");
// Adapt the DateTime here, we will use the current time for this example
DateTime currentDate = DateTime.Now;
// The date in the format that we need
string myDate = DateTime.Parse(currentDate.ToString(), currentCulture).ToString(myLanguage);

Convert DateTime

This works:
testDateTime = DateTime.ParseExact("16/10/2010", "dd/MM/yyyy", null);
This does NOT:
string somedate = "16/10/2010";
testDateTime = DateTime.ParseExact(somedate, "dd/MM/yyyy", null);
why??

Both code snippets are absolutely equivalent and should work/not work the same. I suspect that the value of the somedate variable is not what you think it is inside your application. Try debugging.

Both of your examples are equivalent, and should work if your current culture is en-US, but not necessarily in all other cultures.
For example, the following will throw a FormatException because the de-DE culture uses period as a separator (16.10.2010):
System.Threading.Thread.CurrentThread.CurrentCulture =
CultureInfo.CreateSpecificCulture("de-DE");
DateTime testDateTime = DateTime.ParseExact("16/10/2010", "dd/MM/yyyy", null);
In general it's good practice (FxCop will warn about it) to always specify the IFormatProvider parameter when it's available: usually either CultureInfo.CurrentCulture if you're parsing input from the current user; or CultureInfo.InvariantCulture if you're parsing input from an external source.
// For input from the current user (16.10.2010 in Germany)
testDateTime = DateTime.ParseExact("16/10/2010", "dd/MM/yyyy", CultureInfo.CurrentCulture);
// For input from an external source in a defined culture-invariant format
testDateTime = DateTime.ParseExact("16/10/2010", "dd/MM/yyyy", CultureInfo.InvariantCulture);

It worked fine when I tried it... Just copied and pasted it.
Insert a breakpoint, put your pointer over the variable and check the month, day and year member. If they are not rights, show us what you see.
If you are using a print or msgbox to show the value of the variable, maybe you are not suplying a mask/format for the output.

You are trying to change the DateTime format right? You can not do that with a DateTime object. You can change the format only when you display the DateTime object using String.Format: String.Format("{0:d/M/yyyy HH:mm:ss}", dt). (for example or other methods)

Both the things worked for me when I tried. What is the error you are getting?
The ParseExact() uses the second parameter to parse your input string and not to return the value in that format.
EDIT: from Joe's comment below - The output you get will be in "MM/dd/yyyy" format" - the output will be a DateTime type that doesn't have any intrinsic format.

for some reason it would not work for me UNTIL i added this: CultureInfo.InvariantCulture
DateTime.ParseExact(sValue, "dd/MM/yyyy", CultureInfo.InvariantCulture);