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How to Convert date into String format to Date format in C#?

I am trying to convert this ("2019-09-09"(yyyy-MM-dd)) string into date format. I am using DateTime.ParseExact method, but it is not giving me the expected output.
string transactionDateFrom = "2019-09-09";
var provider = CultureInfo.InvariantCulture;
var c = DateTime.ParseExact(transactionDateFrom, "yyyy-MM-dd", provider);
But it shows output as (09/09/2019 12:12Am) I just need format like (yyyy-MM-dd) and it must be date format not string.

You should also provide format for ToString or whenever you use that, since right now you only use it for parsing.
You may also just edit the culture the following way:
CultureInfo culture = (CultureInfo) CultureInfo.CurrentCulture.Clone();
culture.DateTimeFormat.ShortDatePattern = "yyyy-MM-dd";
culture.DateTimeFormat.LongTimePattern = "yyyy-MM-dd";

You should either use DateTime.TryParseExact or use DateTime.TryParse specifying the appropriate CultureInfo.
(For E.g., the culture of the user.)
You can use DateTime.ParseExact method overloads and you can specify exact format and proper (that uses / as a DateSeparator) culture information.
Also be aware that the Difference between M and MM specifiers.
For single digit month numbers, MM specifier will generate month number with leading zero (like 09) but M specifier won't.
string strDate = "2019-09-28";
DateTime date = DateTime.ParseExact(strDate, "yyyy-MM-dd", System.Globalization.CultureInfo.InvariantCulture);
string Format = date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture);
OR
string strDate = "2019-9-28";
DateTime date = DateTime.ParseExact(strDate, "yyyy-M-dd", System.Globalization.CultureInfo.InvariantCulture);
string Format = date.ToString("yyyy-M-dd", CultureInfo.InvariantCulture);

How to define DateTime parse format for general date format with optional time part?

What is the right DateTime format to parse a date from string in general date format ("G") with optional time part ("d")?
I can have two types of dates:
"12/13/2012 6:30:00 PM"
"3/29/2013"
How to parse them in unified way?
Right now I'm trying to parse with "G" format and then if it not parsed with "d" format.

If your CurrentCulture supports MM/dd/yyyy h:mm:ss tt (I assume your LongTimePattern has h) and M/dd/yyyy (I assume your ShortDatePattern has M) as standard date and time format, using DateTime.TryParse(String, out DateTime) method can solve all your problems.
string s = "";
DateTime dt;
if (DateTime.TryParse(s, out dt))
{
// Your string parsed successfully.
}
If these formats doesn't standard date and time format for your CurrentCulture, using DateTime.TryParseExact(String, String[], IFormatProvider, DateTimeStyles, DateTime) overload can be the best choice because it takes formats part as a string array. That means, you can provide multiple formats and your string will be parsed with first successful match.
string s = "";
string[] formats = { "MM/dd/yyyy h:mm:ss tt", "M/dd/yyyy" };
DateTime dt;
if (DateTime.TryParseExact(s, formats, CultureInfo.CurrentCulture,
DateTimeStyles.None, out dt))
{
// Your string parsed with one of speficied format.
}
Be careful when you parse string that have "/" custom format specifier. It has a special meaning of replace me with current culture or specified culture date separator. That means if your CurrentCulture's DateSeparator property is not /, your parsing operation will fail even if your string and formats are the same format.

Just use DateTime.Parse() or if you want to do a safe parse attempt DateTime.TryParse()
DateTime dt1, dt2;
dt1 = DateTime.Parse("12/13/2012 6:30:00 PM");
dt2 = DateTime.Parse("3/29/2013");
OR
DateTime.TryParse("12/13/2012 6:30:00 PM", out dt1);
DateTime.TryParse("3/29/2013", out dt2);
You only have to use DateTime.ParseExact() or provide the format if it differs from the accepted formats that DateTime.Parse() accepts, or if you only allow one particular format.

Converting string to date time

I have a date which comes in a string like so:
09/25/2014 09:18:24
I need it like this (yyyy-mm-dd):
2014-09-25 09:18:24
The object that this date goes into is a nullable date.
Tried this does not work:
DateTime formattedDate;
bool result = DateTime.TryParseExact(modifiedDate, "yyyy-MM-dd",
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out formattedDate);
Any clues?
Thanks in advance.

From DateTime.TryParseExact
Converts the specified string representation of a date and time to its
DateTime equivalent. The format of the string representation must
match a specified format exactly.
In your case, they are not. Use yyyy-MM-dd HH:mm:ss format instead.
string s = "2014-09-25 09:18:24";
DateTime dt;
if(DateTime.TryParseExact(s, "yyyy-MM-dd HH:mm:ss",
CultureInfo.InvariantCulture,
DateTimeStyles.None, out dt))
{
Console.WriteLine(dt);
}
It is a little bit unclear but if your string is 09/25/2014 09:18:24, then you can use MM/dd/yyyy HH:mm:ss format instead. Just a tip, "/" custom format specifier has a special meaning as replace me with current culture or supplied culture date separator. That means, if your CurrentCulture or supplied culture's DateSeparator is not /, your parsing operation will fail even if your format and string matches exactly.
If you have already a DateTime and you want to format it, you can use DateTime.ToString(string) method like;
dt.ToString("yyyy-mm-dd", CultureInfo.InvariantCulture); // 2014-09-25
or
dt.ToString("yyyy-mm-dd HH:mm:ss", CultureInfo.InvariantCulture); // 2014-09-25 09:18:24
Remember, a DateTime does not have any implicit format. It just contains date and time values. String representations of them have formats.

In answer to your question, to convert it as you prefer, do it like this:
string originalDate = "09/25/2014 09:18:24";
DateTime formattedDate;
if (DateTime.TryParseExact(originalDate, "MM/dd/yyyy HH:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.None, out formattedDate))
{
string output = formattedDate.ToString("yyyy-mm-dd HH:mm:ss", CultureInfo.InvariantCulture);
}
And then output will have your desired format.

DateTime dateOf = Convert.ToDateTime("09/25/2014 09:18:24");
string myFormat = "yyyy-mm-dd";
string myDate = dateOf.ToString(myFormat); // output 2014-18-25
Datetime format

Convert a string to DateTime in C#

I am trying to convert a string to a DateTime for some hours now,
The string looks like this
"20140519-140324" and I know its in UTC
I've allready tried this
DateTime ourDateTime;
bool success = DateTime.TryParseExact(Date, "yyyy-MM-dd-HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal, out ourDateTime);
StartTime.Text = ourDateTime.ToString("g");
and this
DateTime ourDateTime= DateTime.ParseExact(Date, "yyyy-MM-dd-HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture);
StartTime.Text = ourDateTime.ToString("g");
but none of these work. What I am not doing properly?

From DateTime.TryParseExact method
Converts the specified string representation of a date and time to its
DateTime equivalent. The format of the string representation must
match a specified format exactly.
In your example, they are not. Use yyyyMMdd-HHmmss custom format instead which exactly matches with your string.
Here an example on LINQPad;
string s = "20140519-140324";
DateTime dt;
if(DateTime.TryParseExact(s, "yyyyMMdd-HHmmss", CultureInfo.InvariantCulture,
DateTimeStyles.AdjustToUniversal, out dt))
{
dt.Dump();
}
Here a demonstration.
Your DateTime.ParseExact example also won't work because of the same reason.
For more information;
Custom Date and Time Format Strings

You are using the wrong format in the TryParseExact method.
the format parameter should be an indicator to the format of the input string.
therefor you need to do this:
DateTime ourDateTime;
bool success = DateTime.TryParseExact(Date, "yyyyMMdd-HHmmss", System.Globalization.CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal, out ourDateTime);
if(success) {
StartTime.Text = ourDateTime.ToString("g");
}

Parse string value to datetime value

I need to parse string value to date time value, I have date in this format:
DD.MM.YYYY
I want to parse value in this format:
YYYY-MM-DD
I tried to do it like this:
DateTime.ParseExact(date_req, "yyyy-MM-dd", CultureInfo.InvariantCulture);
But i have an error: String was not recognized as a valid DateTime.
Is there a way to do this?

If you have a string in the format DD.MM.YYYY why are you passing YYYY-MM-DD to your ParseExact function?
Try like this:
string dateStr = "12.06.2012";
DateTime date = DateTime.ParseExact(dateStr, "dd.MM.yyyy", CultureInfo.InvariantCulture);
Then when you want to output this DateTime instance somewhere you could use the YYYY-MM-DD format, like this:
string result = date.ToString("yyyy-MM-dd");

I think what you want to do is parse your dd.MM.yyyy and then display it as yyyy-MM-dd.
You first have to parse the string into a DateTime:
DateTime date = DateTime.ParseExact(date_req, "yyyy-MM-dd", CultureInfo.InvariantCulture);
Now date is a representation of the date that the computer actually understands (before it was just a string). You can now display this object anyway you want:
string yyyyMMdd = date.ToString("yyyy-MM-dd");
string arabic = date.ToString("yyyy-MM-dd", new CultureInfo("ar"));
// and so on
Don't forget that when converting dates from strings to DateTime and back, culture and time zones are worth keeping in mind.

When parsing a date you need to specify the format you want to read, not the format you want as output later.
So use dd.MM.yyyy as argument to ParseExact.

Check DateTime.ParseExact Method (String, String,
IFormatProvider) Converts the specified string representation
of a date and time to its DateTime equivalent. The format of the
string representation must match a specified format exactly or an
exception is thrown.
you have to specify format string as DD.MM.YYYY rather than "yyyy-MM-dd".
try this:
DateTime dateValue = DateTime.ParseExact(date_req, "DD.MM.YYYY", CultureInfo.InvariantCulture );
// use this when you need to show that formatted date value
string formattedDate = dateValue.ToString("yyyy-MM-dd");
Better way is that use DateTime.TryParseExact Method, if you want it as date rather than string modify your culture info and date separator.
CultureInfo enUS = new CultureInfo("en-US");
string dateString;
DateTime dateValue;
dateString = "05.01.2009";
if (DateTime.TryParseExact(dateString, "DD.MM.YYYY", enUS,
DateTimeStyles.None, out dateValue))
Console.WriteLine("Converted '{0}' to {1} ({2}).", dateString, dateValue,
dateValue.Kind);
else
Console.WriteLine("'{0}' is not in an acceptable format.", dateString);

First parse it in the existing format then convert to the string format you want.
var date = DateTime.ParseExact(date_req, "dd.MM.yyyy", CultureInfo.InvariantCulture);
var str = date.ToString("yyyy-MM-dd");

You can first convert it to a character array. then you can parse day/month/year separately to integers . You know the indexes of the numbers so this will be easy. after that you can concatenate every element in the way you like.

Error. You have a cake and you want to eat a stake. In order to convince your stomach that that the cake is a stake you have to transform the cake to a stake. This cannot be done. Parsing is about accepting a value as it comes and use a pattern (or more) to translate it to something else and not transform it. So what you want may be right but you ask is wrong.