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Date was not recognized as a valid DateTime

kinda got an issue that I cant solve right now.
I've got a discord bot running on my raspberry pi, which has a system for automated messages that are sent after a certain amount of time, or an exact date, has passed.
My code works on Windows when debugging there, but the console throws a warning on Linux when running the published project.
The date is taken from a table in my MySQL database and put into a DataTable. The code that grabs the date from the DataRow is:
DateTime datetime = DateTime.ParseExact(row["datetime"].ToString(), "dd.MM.yyyy HH:mm:ss", CultureInfo.InvariantCulture);
Why is it happening? No matter how I format the string (dots, dashes or slashes), the warning persists. The messages are not sent.
I even tried removing invisible whitespaces with regex, doesnt work either.
(The regex in question, though I scrapped it since it yielded no fruit anyways)
Regex.Replace($"{row["datetime"].ToString()}", #"[^\d\s\.:]", string.Empty);

If RDBMS type is DateTime then why should we convert to string and then parse it back to DateTime? Let's do it direct:
DateTime datetime = Convert.ToDateTime(row["datetime"]);
and let .net convert boxed DateTime (row["datetime"] is of type object?) to DateTime

There are a couple issues--at the highest level, your ParseExact method is encountering a Date Time string that does not match the supplied format.
According to the code you posted, the expected format of is dd.MM.yyyy HH:mm:ss, and in your exception exception, shows a Date time string (8/2/2021 2:00:00 PM) that does not match:
contains / and your expected format has .
dd is a 2-digit day, but the input date time string only has single digit days
MM expects a two digit month and the input date time only has a single digit month
the string contains AM/PM, and your format neglects to account for that.
Finally it's not clear if your date format is Month Day Year, or Day Month year.
The second issue, is that ParseExact should be enclosed in a try/catch block, so that your code can handle the case when an unexpected formatted date time string is passed in, and not crash.
To solve this, wrap your call into a try/catch, and gracefully handle the FormatException
And then make sure the Format string matches the expected input string.
Here is the .NET reference for the various DateTime format tokens

The error message is letting you know the issue.
You have :
DateTime datetime = DateTime.ParseExact(row["datetime"].ToString(), "dd.MM.yyyy HH:mm:ss", CultureInfo.InvariantCulture);
Notable, you are saying that the date format is going to be "dd.MM.yyyy HH:mm:ss"
Then your error message is saying that you couldn't parse :
8/2/2021 2:00:00 PM
Which is essentially a format of "d/M/yyyy h:mm:ss tt" (Assuming that days come before months).
If you change your code to :
DateTime datetime = DateTime.ParseExact(row["datetime"].ToString(), "d/M/yyyy h:mm:ss tt", CultureInfo.InvariantCulture);
You should be good to go. DateTime.ParseExact does what it says on the tin, it parses the date format exactly how you say it should come. If you aren't sure you can use DateTime.Parse() (But you can occassionally run into issues where days/months are around the wrong way).
Tested using the following code :
var myDateString = "8/2/2021 2:00:00 PM";
DateTime datetime = DateTime.ParseExact(myDateString, "d/M/yyyy h:mm:ss tt", CultureInfo.InvariantCulture);
Console.WriteLine(datetime.ToString());

String to DateTime conversion not working

I am converting one string to DateTime variable like this
DateTime selecteddatetest = Convert.ToDateTime("09/21/2017");
This works fine in my production Server, But when I run this code in my local development machine, this throws an error
System.FormatException: 'String was not recognized as a valid DateTime.'
Can anyone please point out what I am missing here?

You could use ParseExact if the time format is consistent:
DateTime.ParseExact("09/21/2017","MM/dd/yyyy",
System.Globalization.CultureInfo.InvariantCulture)

Its probably a localisation issue between the two machines, try specifying the date in the format "2017-09-21" and it should work everywhere.

You are likely using a different culture between the two machines.
For example, the server is using the US culture which expects the format MM/dd/yyyy so your parsing works.
You local machine may be using a culture such as UK which expects the format dd/MM/yyyy and as there is no month 21 it fails.
You can specify the culture explicitly if you know it's always going to be the same:
Convert.ToDateTime("09/21/2017", new System.Globalization.CultureInfo("en-US"));
It may also work with an invariant culture:
Convert.ToDateTime("09/21/2017", System.Globalization.CultureInfo.InvariantCulture);
You may also use ParseExact to specify the desired format:
DateTime.ParseExact("09/21/2017", "MM/dd/yyyy", System.Globalization.CultureInfo.InvariantCulture);

Unable to convert DateTime from SQL Server to C# DateTime

I wrote a program in C# that uses dates. It takes the value from a SQL Server table. I was using Windows 7 and the program worked fine. I had this line of code:
DateTime fechaOperacion = Convert.ToDateTime(reader["FechaOperacion"]);
The reader returned a date in a 24h format and I was able to convert that to a DateTime variable.
Now I did a system upgrade to Windows 10 and that same line of code is throwing the following error:
String was not recognized as a valid DateTime. there is an unknown word starting at index 20.
And now the reader returns a.m. / p.m. format, and at index 20 there is a.m or p.m.
I have tried the following things:
Rephrasing the line of code to:
Convert.ToDateTime(reader["FechaOperacion"], System.Globalization.CultureInfo.InvariantCulture)
reader.GetDateTime(reader.GetOrdinal("FechaOperacion"));
Convert the culture to 24h format
System.Threading.Thread.CurrentThread.CurrentCulture = new CultureInfo(1033);
But none of that seems to work, I don't know what else to do.

Ultimately, the underlying problem here is storing a value that represents a date/time as textual data (meaning, some kind of [n][var]char({max|n}), or at a push: [n]text). This has multiple problems:
it takes more space
it cannot be sorted correctly / efficiently
it cannot be indexed correctly / efficiently
it cannot be filtered correctly / efficiently
it leads to parsing errors between client and server
it has all sorts of localization and internationalization problems
What you should have is a datetime / date / time / etc column. This is then stored as a number (not a string) that requires zero parsing and will work reliably without any conversion problems.
Note: it could be that you are storing it correctly but formatting it inside the select statement of your query. In which case, just don't do that; return the date-time raw, and let the receiving client worry about how to display it.

Depending on your actual format, you can define a suitable format list and do a conversion like below
string[] mfs = { "MM/dd/yyyy HH:mm:ss", "MM/dd/yyyy h:mm:ss tt"};
var dat = DateTime.ParseExact("04/23/1945 8:45:22 PM", mfs,
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None);

How does DateTime.TryParse know the date format?

Here is a scenario.
You have a string that represents a date i.e. "Jan 25 2016 10:10 AM".
You want to know whether it represents a date in a specific culture.
You want to know what dateTime pattern satisfies this date string.
Example:
Date string is "Jan 25 2016 10:10 AM"
Culture is en-US
The POSSIBLE format for it could be "MMM dd yyyy HH:mm tt"
Implementation:
To get the list of all dateTime patterns you can get a CultureInfo.DateTimeFormat.GetAllDateTimePatterns()
Then try the overloaded version of DateTime.TryParseExact(dateString, pattern, culture, DateTimeStyles.None, out resultingDate) for each of the patterns above and see whether it can parse a date.
That should give you the needed dateTime pattern.
HOWEVER if we iterate all those patterns it will not find any matches!
This is even more weird if you try and use a DateTime.TryParse(dateString, culture, DateTimeStyles.None, out resultingDate) and it DOES parse the correct date!
So the question is how come the DateTime.TryParse knows the pattern of a date string when this info is not a part of CultureInfo and how to get to this info in a culture?
Thanks!

I agree with xanatos, there is no perfect solution for that and you can't assume that every format GetAllDateTimePatterns returns can be perfectly parsable with Parse or TryParse methods.
From DateTimeFormatInfo.GetAllDateTimePatterns;
You can use the custom format strings in the array returned by the
GetAllDateTimePatterns method in formatting operations. However, if
you do, the string representation of a date and time value returned in
that formatting operation cannot always be parsed successfully by the
Parse and TryParse methods. Therefore, you cannot assume that the
custom format strings returned by the GetAllDateTimePatterns method
can be used to round-trip date and time values.
If you see Remarks section on the page, there are only 42 formats that can be parsed by TryParse method in 96 formats that GetAllDateTimePatterns method returns for it-IT culture for example.7
Tarek Mahmoud Sayed responded as;
Parse/TryParse are implemented as finite state machine so it doesn’t
really use the date patterns in parsing. It just split the parsed
string into tokens and try to find if the token match specific part of
the date (like Month, day, day of week…etc.). in the other hand
ParseExact/TryParseExact will just parse the string according to the
passed format pattern.

In short, Parsing is really hard because there are a lot of things that can trip it up. And someone in some government could suddenly decide that country X should use D/M/Y instead of M/D/Y, or could have someone entering data used to the other format.
I talk a little about this on a blog post (toward the bottom-ish) https://web.archive.org/web/20190110065542/https://blogs.msdn.microsoft.com/shawnste/2005/04/05/culture-data-shouldnt-be-considered-stable-except-for-invariant/
DateTime.Parse attempts to guess what the input might be based on the pattern(s) and separators it sees in the specified culture. Unfortunately, some cultures are REALLY hard to guess at. For example, . has been used for time formats in some locales, so is 1.1.1 12.12.12 the 12th day of December 2012? Or the 1st day of January 2001?
ParseExact (as the other answers suggest) is more reliable as you can tell it exactly what you're looking for - even better, you can also tell the user exactly what to enter. (Hopefully this is human input). Unfortunately it requires the user to follow the template.
This is also why most date controls you encounter, especially on the web, have separate fields for month, day & year.
For machine readable formats its best to spit it out in some standard format and read it back in with that exact same format. We've had customers send data from one country to another using the CurrentCulture and wonder why their vendor can't read it ;-)

String was not recognized as a valid DateTime

I know such questions are in ton in SO but my situation seems little weird to me.
I have a textbox with a calendar extender control on my aspx page
Default format is "d" in extenders date format property.
When I choose my date say 15th May 2012 from the calendar,it gives me 5/15/2012, which is fine.
Since its a string and my db field is oftype datetime, so I am using
Convert.ToDateTime(TextBox.Text); // TextBox.Text = 5/15/2012
But it throws the exception,
string was not recognized as valid datetime.
I then Change the code and used DateTime.Parse() but the issue remains. Then i tried to reformat the date something like this,
Convert.ToDateTime(string.Format("0:MM-dd-yyyy",TextBox.Text)).Date
but still its throwing exceptions..
Please help me.

Use the following,
DateTime dt = DateTime.ParseExact(TextBox.Text, "dd/MM/yyyy",
CultureInfo.InvariantCulture);
There's probably a difference between your system's DateTime format and the DateTiem format the extender uses.

I suppose that your dev machine date-time format is not equal to MM/DD/YYYY, but something else (for example DD/MM/YYYY). Have a look on your computer Regional settings to see your system date time format.