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c# convert yyyymmdd text to dd/MM/yyyy

I have some text in rows as yyyymmdd (eg: 20181211) which I need to convert to dd/MM/yyyy
I am using:
cashRow["BusinessDate"] = Convert.ToDateTime(row.Cells[ClosingDate.Index].Value.ToString()).ToString("dd/MM/yyyy");
I get the error "string was not recognized as a valid DateTime.
Any ideas where I am going wrong?

You'll need to use ParseExact (or TryParseExact) to parse the date:
var date = "20181217";
var parsedDate = DateTime.ParseExact(date, "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);
var formattedDate = parsedDate.ToString("dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture)
Here we tell ParseExact to expect our date in yyyyMMdd format, and then we tell it to format the parsed date in dd/MM/yyyy format.
Applying it to your code:
cashRow["BusinessDate"] = DateTime.ParseExact(row.Cells[ClosingDate.Index].Value.ToString(), "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture).ToString("dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture);

You have to use ParseExact to convert your yyyyMMdd string to DateTime as follows and then everything is okay.
cashRow["BusinessDate"] = DateTime.ParseExact(row.Cells[ClosingDate.Index].Value.ToString(), "yyyyMMdd", CultureInfo.InvariantCulture).ToString("dd/MM/yyyy");

As you already know the exact format of your input yyyyMMdd (eg: 20181211), just supply it to DateTime.ParseExact() and then call ToString() on the returned DateTime object.
string YourOutput = DateTime.ParseExact(p_dates, "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture).ToString("dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture);

Try this:
cashRow["BusinessDate"] = row.Cells[ClosingDate.Index].Value.ToString("dd/MM/yyyy");

System.FormatException: String was not recognized as a valid DateTime - when trying to convert MM/DD/YYYY

I have following C# method:
DateTime ConvertStringToDate(string dateInString)
{
try {
//string SSD = dateInString;
//DateTime date = Convert.ToDateTime(SSD);
//string strDate = String.Format("{0:yyyy-MM-dd HH:mm:ss.fff}", date);
//return Convert.ToDateTime(strDate);
return DateTime.ParseExact(dateInString, "MM/dd/yyyy", CultureInfo.InvariantCulture);
}
catch (Exception) { }
return DateTime.Today;
}
The code in comment is another way I tried before.
I am in India and developing an ASP.NET WebForms application for my client in US. On one of its forms my client will enter the date in TextBox like 6/20/2018 which is MM/dd/yyyy format.
But in both the ways I am getting this error: System.FormatException: 'String was not recognized as a valid DateTime.'
I tried many solutions on SO but none of them are working.

return DateTime.ParseExact(dateInString, "M/d/yyyy", CultureInfo.InvariantCulture);
Check it here
The difference between my answer and Fabulous' one is that I also shortened dd to d so if your user writes 6/6/2018 it will work too

Your date format is MM/dd/yyyy and your input doesn't match. It is M/dd/yyyy
Based on your comment, to solve the 6/1/2018 issue, you'll need to do it as follows M/d/yyyy

Your format string is missing the AM/PM deisgnator:
return DateTime.ParseExact
(dateInString + " 12:00:00 AM", "MM/dd/yyyy hh:mm:ss tt", CultureInfo.InvariantCulture);
// Here ---------------------------------------------^

Try without concatenation with string " AM"

I was getting the same exception a couple of days ago when it was 9th of July, I simply appended a 0 with 9 to match the date format.
Try appending a 0 in your month to match the MM in your date format

Sometimes your system time and date format is not same as test format you can try to change system date and time format

If you want to convert this (01-01-2022) type of string into date
then try below code.
DateTime date = DateTime.ParseExact("01-01-2022", "MM-dd-yyyy", CultureInfo.InvariantCulture);
If you want to convert this (01/01/2022) type of string into date
then try below code.
DateTime date = DateTime.ParseExact("01-01-2022", "MM/dd/yyyy", CultureInfo.InvariantCulture);

convert to stamp time format from string c#

I use javascript to pick a date and display the format as (11-05-2015 17:37)
and I try to parse it to date time as the code below
DateTime taskDate = Convert.ToDateTime(txtDate.Text);
and save it into my date base like
TO_DATE('" + createOn + "')
its give me and error call "String was not recognized as a valid DateTime."
anyone have any others method to parse it to stamptime ?
the txtDate.Text value is 27-05-2015 09:37.

Convert.ToDateTime uses your current thread culture format when converting from string to datetime.
If string you converting from has another format, you need to use DateTime.ParseExact and explicitly provide appropriate format.
For example, in you case it should be
DateTime taskDate = DateTime.ParseExact("11-05-2015 17:37", "dd-MM-yyyy HH:mm", CultureInfo.InvariantCulture);
Also have a look to custom datetime format strings for your reference.

You can use DateTime.ParseExact or DateTime.TryParseExact
Check below code:
DateTime taskDate = DateTime.ParseExact(txtDate.Text, "dd-MM-yyyy hh:mm", CultureInfo.InvariantCulture);
Or
DateTime taskDate;
if (DateTime.TryParseExact(txtDate.Text, "dd-MM-yyyy hh:mm", CultureInfo.InvariantCulture, DateTimeStyles.None, out taskDate))
{
//code if date valid
}
else
{
//code if date invalid
}

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

DateTime Converting

I am trying to convert a string into a DateTime and change its format from 05/06/2012 12:00:00 to 2012-06-05 12:00:00.000 to search in the database (SQL Server 2008 R2) DATETIME column type. The original date is coming from a calendar!
I tried this:
string Datereturn = row.Cells[9].Text;
DateTime dategiven = DateTime.ParseExact(Dategiven,
"YYYY-MM-DD hh:mm:ss[.nnn]", CultureInfo.InvariantCulture);
but it pops an error of invalid datetime

To parse 05/06/2012 12:00:00:
DateTime dategiven = DateTime.ParseExact(Dategiven,
"dd/MM/yyyy hh:mm:ss", CultureInfo.InvariantCulture);
To get a different formatted string:
string newFormat = dateGive.ToString("yyyy-MM-dd hh:mm:ss");
I suggest reading Custom Date and Time Format Strings on MSDN.
Also the different between parsing and formatting (in regards to DateTime):
Parsing means taking a string representing a datetime and getting a DateTime object from it
Formatting a DateTime is taking a DateTime object and getting a string from it, formatted as needed.

Can you try this
DateTime dategiven = DateTime.ParseExact(Dategiven, "dd/MM/yyyy hh:mm:ss", CultureInfo.InvariantCulture);