Develop Reference

How to convert string to given date format

The below code is in MM/DD/YYYY format
string dateStr="9/7/1986";
But i want to change it like below format
dateStr="09/07/1986";
again same in MM/DD/YYYY format

This code should work for you.
string dateStr = "9/7/1986";
string newDateStr= DateTime.Parse(dateStr).ToString("MM/dd/yyyy");
newDateStr will hold the value you need.
The best thing to do would be to use that format when you first convert the DateTime value to a string. Although, this would only work if you had it as a DateTime variable first.

You could parse it to a DateTime then format it back to a string.
dateStr = DateTime.ParseExact(dateStr, "M/d/yyyy", CultureInfo.InvariantCulture)
.ToString("MM/dd/yyyy");
Note that you'll get exceptions if the string doesn't match the M/d/yyyy format.

Retaining MM/DD/YYYY format in String

I need to write date in MM/DD/YYYY format. From a Date Picker Control. I try to assign it to a DateTime variable. Before Writing it to a file I assign it to a string. I see the value stored in String variable is in DD/MM/YYYY format.
Below is assignment statement
DateTime startTime, endTime;
string startTimeDate = "";
startTime = Convert.ToDateTime(dpStartTime.Value.ToString("MM/dd/yyyy HH:mm"));
endTime = Convert.ToDateTime(dpEndTime.Value.ToString("MM/dd/yyyy HH:mm"));
startTimeDate = startTime.ToString("MM/dd/yyyy HH:mm");
startTimeDate = startTimeDate.Replace('-', '/');
I observe startTimeDate is stored as DD/MM/YYYY only. startTime is storing as MM/DD/YYYY format only. Please let me know if there is any other approach to correctly assign / convert the date values.
Thanks in Advance

Edit:
You are losing the original date in your Convert.DateTime() conversion, you have to apply the format string here as well e.g. using DateTime.ParseExact :
startTime = DateTime.ParseExact(dpStartTime.Value.ToString("MM/dd/yyyy HH:mm"),
"MM/dd/yyyy HH:mm",
CultureInfo.InvariantCulture);

Instead of using Convert.ToDateTime(), try to use DateTime.ParseExact(string s, string format, IFormatProvider provider) when you can ensure the datetime format and want to ignore the system settings. MSDN Reference for the DateTime.ParseExact() method can be found here

You're converting DateTime to string, then you're converting it again to DateTime using Convert class. You're not preserving the format here cause DateTime is format agnostic. And default ToString conversion (used by debugger) is in your cause MM/DD/YYYY.

I usually use String.Format, ex
String.Format("{0:d/M/yyyy HH:mm:ss}", dpStartTime.Value);
To format dates as strings.

C# Date Parse Exact mindate issues

I have the following function
DateTime fromDateParam = DateTime.ParseExact(Convert.ToString(DateTime.MinValue),"dd.MM.yyyy HH:mm:ss",null);
It says input string not recognised as a valid date.
Any ideas how I can get any the min date recognised to parse exact?

Well you're converting the original time to a string using the default formatting, but then you're specifying custom formatting for the parsing.
If you specify a format string using DateTime.ToString(format) and keep the format consistent, it works fine:
string formatString = "dd.MM.yyyy HH:mm:ss";
string text = DateTime.MinValue.ToString(formatString);
Console.WriteLine(text);
DateTime fromDateParam = DateTime.ParseExact(text, formatString, null);

In other words (continuing Skeet's answer), Convert.ToString(DateTime.MinValue) is based on current/default CultureInfo, etc.

String was not recognized as a valid DateTime " format dd/MM/yyyy"

I am trying to convert my string formatted value to date type with format dd/MM/yyyy.
this.Text="22/11/2009";
DateTime date = DateTime.Parse(this.Text);
What is the problem ?
It has a second override which asks for IFormatProvider. What is this? Do I need to pass this also? If Yes how to use it for this case?
Edit
What are the differences between Parse and ParseExact?
Edit 2
Both answers of Slaks and Sam are working for me, currently user is giving the input but this will be assured by me that they are valid by using maskTextbox.
Which answer is better considering all aspects like type saftey, performance or something you feel like

Use DateTime.ParseExact.
this.Text="22/11/2009";
DateTime date = DateTime.ParseExact(this.Text, "dd/MM/yyyy", null);

You need to call ParseExact, which parses a date that exactly matches a format that you supply.
For example:
DateTime date = DateTime.ParseExact(this.Text, "dd/MM/yyyy", CultureInfo.InvariantCulture);
The IFormatProvider parameter specifies the culture to use to parse the date.
Unless your string comes from the user, you should pass CultureInfo.InvariantCulture.
If the string does come from the user, you should pass CultureInfo.CurrentCulture, which will use the settings that the user specified in Regional Options in Control Panel.

Parsing a string representation of a DateTime is a tricky thing because different cultures have different date formats. .Net is aware of these date formats and pulls them from your current culture (System.Threading.Thread.CurrentThread.CurrentCulture.DateTimeFormat) when you call DateTime.Parse(this.Text);
For example, the string "22/11/2009" does not match the ShortDatePattern for the United States (en-US) but it does match for France (fr-FR).
Now, you can either call DateTime.ParseExact and pass in the exact format string that you're expecting, or you can pass in an appropriate culture to DateTime.Parse to parse the date.
For example, this will parse your date correctly:
DateTime.Parse( "22/11/2009", CultureInfo.CreateSpecificCulture("fr-FR") );
Of course, you shouldn't just randomly pick France, but something appropriate to your needs.
What you need to figure out is what System.Threading.Thread.CurrentThread.CurrentCulture is set to, and if/why it differs from what you expect.

Although the above solutions are effective, you can also modify the webconfig file with the following...
<configuration>
<system.web>
<globalization culture="en-GB"/>
</system.web>
</configuration>
Ref : Datetime format different on local machine compared to production machine

You might need to specify the culture for that specific date format as in:
Thread.CurrentThread.CurrentCulture = new CultureInfo("en-GB"); //dd/MM/yyyy
this.Text="22/11/2009";
DateTime date = DateTime.Parse(this.Text);
For more details go here:
http://msdn.microsoft.com/en-us/library/5hh873ya.aspx

Based on this reference, the next approach worked for me:
// e.g. format = "dd/MM/yyyy", dateString = "10/07/2017"
var formatInfo = new DateTimeFormatInfo()
{
ShortDatePattern = format
};
date = Convert.ToDateTime(dateString, formatInfo);

After spending lot of time I have solved the problem
string strDate = PreocessDate(data);
string[] dateString = strDate.Split('/');
DateTime enter_date = Convert.ToDateTime(dateString[1]+"/"+dateString[0]+"/"+dateString[2]);

private DateTime ConvertToDateTime(string strDateTime)
{
DateTime dtFinaldate; string sDateTime;
try { dtFinaldate = Convert.ToDateTime(strDateTime); }
catch (Exception e)
{
string[] sDate = strDateTime.Split('/');
sDateTime = sDate[1] + '/' + sDate[0] + '/' + sDate[2];
dtFinaldate = Convert.ToDateTime(sDateTime);
}
return dtFinaldate;
}

use this to convert string to datetime:
Datetime DT = DateTime.ParseExact(STRDATE,"dd/MM/yyyy",System.Globalization.CultureInfo.CurrentUICulture.DateTimeFormat)

Just like someone above said you can send it as a string parameter but it must have this format: '20130121' for example and you can convert it to that format taking it directly from the control. So you'll get it for example from a textbox like:
date = datetextbox.text; // date is going to be something like: "2013-01-21 12:00:00am"
to convert it to: '20130121' you use:
date = date.Substring(6, 4) + date.Substring(3, 2) + date.Substring(0, 2);
so that SQL can convert it and put it into your database.

Worked for me below code:
DateTime date = DateTime.Parse(this.Text, CultureInfo.CreateSpecificCulture("fr-FR"));
Namespace
using System.Globalization;

You can use also
this.Text = "22112009";
DateTime newDateTime = new DateTime(Convert.ToInt32(this.Text.Substring(4, 4)), // Year
Convert.ToInt32(this.Text.Substring(2,2)), // Month
Convert.ToInt32(this.Text.Substring(0,2)));// Day

Also I noticed sometimes if your string has empty space in front or end or any other junk char attached in DateTime value then also we get this error message

C# Date Parse Exact Issue

The following code produces an error, any ideas why?
string dateFormatString = "dd.MM.yyyy HH:mm:ss";
string properDate = DateTime.ParseExact(DateTime.Now.ToString() , dateFormatString , null ).ToString()
Error is: String is not recognised as a valid date and time.

DateTime.Now.ToString() formats the date using the current culture. You need to specify the same format: DateTime.Now.ToString("dd.MM.yyyy HH:mm:ss") that's expected by the ParseExact function.

You just need this - rest is piece of cake.
http://john-sheehan.com/blog/wp-content/uploads/msnet-formatting-strings.pdf
and this http://msdn.microsoft.com/en-us/library/w2sa9yss.aspx

Does your local culture write dates as "dd.MM.yyyy HH:mm:ss" ? Simply: if the date's ToString() doesn't produce this layout, then it won't parse cleanly - and ParseExact is not very forgiving.
I'm wondering if you actually want to call:
string s = DateTime.Now.ToString("dd.MM.yyyy HH:mm:ss");

You could simply do:
string dateFormatString = "dd/MM/yyyy HH:mm:ss";
string properDate = DateTime.Now.ToString(dateFormatString);
EDIT: According to your comments, you are trying to match the format to that common in the Czech Republic. You should use CultureInfo to do do that:
string properDate = DateTime.Now.ToString(new CultureInfo("cs-CZ"));