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Inconsistency when parsing DateTime in the same format

I have the following strings:
10/10/2021 00:00:00 and 18/11/2021 23:59:59
I have this code:
bool first = DateTime.TryParse("10/10/2021 00:00:00",
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out DateTime firstDate);
bool second = DateTime.TryParse("18/11/2021 23:59:59",
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out DateTime secondDate);
Console.WriteLine(firstDate + " --- " + secondDate);
The output is:
10/10/2021 12:00:00 AM --- 1/1/0001 12:00:00 AM
As you can see the second date is not properly parsed, even though it's in the same format. What is the reason for that and how can I fix it?

As you can see the second date is not properly parsed, even though it's in the same format.
Here my two cents.
Programming languages and frameworks are not smart enough to know which kind of format data you applied, specially for dates, times, numbers etc.. If you provide these data, you kinda have to provide the proper format as well so they can do their job. You "said" the same format, but you didn't apply any format in your code. So, as we humans, we know (at least you told us) but the computer don't know.
Let's look what TryParse(String, IFormatProvider, DateTimeStyles, DateTime) documentation says;
Converts the specified string representation of a date and time to its
DateTime equivalent using the specified culture-specific format
information and formatting style, and returns a value that indicates
whether the conversion succeeded.
You didn't supply format information you supplied IFormatProvider as InvariantCulture. So, what are these "culture specific formats"?
Well, most of them are returns with GetAllDateTimePatterns method (but not all of them) but be aware because documentation says;
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.
So, if you run;
CultureInfo.InvariantCulture.DateTimeFormat.GetAllDateTimePatterns().Dump();
*Dump is just an extension method of LINQPad by the way, it just outputs to the console.
You will get a lot of datetime patterns, but for our case, the important one is we get MM/dd/yyyy HH:mm:ss format for InvariantCulture.
As you can see, your 18/11/2021 23:59:59 data doesn't match with MM/dd/yyyy HH:mm:ss format because there is no 18th month on Gregorian calendar which is a DateTime instance belongs internally.
Your second parsing fails by the way, that's quite different just saying "the second date is not properly parsed" and this is how DateTime.TryParse method works as explained in the documentation;
When this method returns, contains the DateTime value equivalent to
the date and time contained in s, if the conversion succeeded, or
MinValue (which is 1/1/0001 12:00:00 AM) if the conversion failed. The conversion fails if the s
parameter is null, is an empty string (""), or does not contain a
valid string representation of a date and time.
So, best way to handle this to supply a "specific" format using with DateTime.TryParseExact method or one of its overloads like;
bool first = DateTime.TryParseExact("10/10/2021 00:00:00",
"dd/MM/yyyy HH:mm:ss",
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out DateTime firstDate);
bool second = DateTime.TryParseExact("18/11/2021 23:59:59",
"dd/MM/yyyy HH:mm:ss",
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out DateTime secondDate);

The default DateTime format is 'MM/dd/yyyy' and since you have the date in 'dd/MM/yyyy' format it gives you the output.
Maybe try changing the date format input as 11/18/2021 23:59:59

DateTime : parsing unknown format

The following code will output 2018-10-03 16:40:50 (instead of 2018-03-10) :
DateTime dateTime = new DateTime();
DateTime.TryParse("10/03/2018 4:40:50 PM", out dateTime );
MessageBox.Show(dateTime.ToString());
The following code will parse the date correctly (2018-03-10)
dateTime = DateTime.ParseExact("10/03/2018 4:40:50 PM", "dd/MM/yyyy h:mm:ss tt", System.Globalization.CultureInfo.InvariantCulture);
MessageBox.Show(dateTime.ToString());
Is there any way to correctly parse this date without knowing the exact format?
The current culture of the server application is en-ca (English Canada) and I don't know the exact format of the string date to parse. at least is there a way to parse the date without the curious swap between the month and day? Sounds like an easy question but lost a lot of time reading and tried almost anything found here.
Thanks

End up using TryParseExact with an array list of known format. (ugly but it work)
There is no way to detect MM-DD-YYYY versus DD-MM-YYYY. Known limitation (this format is finally not supported by our application)
Thanks!

Transform between datetime formats

I am facing a problem in which I need to transform dates in a given input format into a target one. Is there any standard way to do this in C#?
As an example say we have yyyy.MM.dd as the source format and the target format is MM/dd/yyy (current culture).
The problem arises since I am using a parsing strategy that gives priority to the current culture and then if it fails it tries to parse from a list of known formats. Now say we have two equivalent dates one in the source culture above (2015.12.9) and the other in the current culture (9/12/2015). Then if we attempt to parse this two dates the month will be 12 for the first case and in the second will be 9, so we have an inconsistency (they were supposed to mean be the same exact date).
I believe that if existing it should be something as
DateTime.Convert(2015.12.9, 'yyyy/MM/dd', CultureInfo.CurrentCulture).
Any ideas?
EDIT:
Thank you all for your ideas and suggestions, however the interpretation most of you gave to my question was not quite right. What most of you have answered is a direct parse in the given format and then a conversion to the CurrentCulture.
DateTime.ParseExact("2015.12.9", "yyyy.MM.dd", CultureInfo.CurrentCulture)
This will still return 12 as month, although it is in the CurrentCulture format. My question thus was, is there any standard way to transform the date in yyyy.MM.d to the format MM/dd/yyy so that the month is now in the correct place and THEN parsed it in the target culture. Such function is likely to be unexisting.

DateTime.ParseExact is what you are looking for:
DateTime parsedDate = DateTime.ParseExact("2015.12.9", "yyyy.MM.d", CultureInfo.InvariantCulture);
Or eventualy DateTime.TryParseExact if you're not confident with input string.

I know it's late but I try to explain little bit deep if you let me..
I am facing a problem in which I need to transform dates in any format
to a target one.
There no such a thing as dates in any format. A DateTime does not have any implicit format. It just has date and time values. Looks like you have a string which formatted as date and you want to convert another string with different format.
Is there any standard way to do this in C#?
Yes. You can parse your string with DateTime.ParseExact or DateTime.TryParseExact first with specific format to DateTime and then generate it's string representation with a different format.
As an example say we have yyyy.MM.dd as the source format and the
target format is MM/dd/yyy (current culture).
I didn't understand what is the meaning of current culture in this sentences and I assume you want yyyy not yyy, but you can generate it as I described above like;
string source = "2015.12.9";
DateTime dt = DateTime.ParseExact(source, "yyyy.MM.d", CultureInfo.InvariantCulture);
string target = dt.ToString("MM/dd/yyyy", CultureInfo.InvariantCulture); // 12/09/201
The problem arises since I am using a parsing strategy that gives
priority to the current culture and then if it fails it tries to parse
from a list of known formats.
Since you didn't show any parsing strategy and there is no DateTime.Convert method in .NET Framework, I couldn't any comment.
Now say we have two equivalent dates one in the source culture above
(2015.12.9) and the other in the current culture (9/12/2015). Then if
we attempt to parse this two dates the month will be 12 and in the
second will be 9, so we have an inconsistency.
Again.. You don't have DateTime's. You have strings. And those formatted strings can't belong on any culture. Sure all cultures might parse or generate different string representations with the same format format a format does not belong any culture.
I assume you have 2 different string which different formatted and you wanna parse the input no matter which one it comes. In such a case, you can use DateTime.TryParseExact overload that takes string array for all possible formats as a parameter. Then generate it's string representation with MM/dd/yyy format and a culture that has / as a DateSeparator like InvariantCulture.
string s = "2015.12.9"; // or 9/12/2015
string[] formats = { "yyyy.MM.d", "d/MM/yyyy" };
DateTime dt;
if (DateTime.TryParseExact(s, formats, CultureInfo.InvariantCulture,
DateTimeStyles.None, out dt))
{
Console.WriteLine(dt.ToString("MM/dd/yyyy", CultureInfo.InvariantCulture));
}

The Simple and Best way to do it is Using .ToString() Method
See this code:
DateTime x =DateTime.Now;
To Convert This Just Write like This:
x.ToString("yyyyMMdd")//20151210
x.ToString("yyyy/MM/dd)//2015/12/10
x.ToString("yyyy/MMM/dd)//2015/DEC/10 //Careful About M type should be capital for month .
Hope helpful

convert date string to datetime

I have date string in format dd-MMM-yyyy and want to convert this to datetime, when I use below code
DateTime.ParseExact("20-Oct-2012", "yyyy-MM-dd HH:mm tt", null)
it causing an error
String was not recognized as a valid DateTime.
When I modify above code
DateTime.ParseExact("20-Oct-2012", "dd-MMM-yyyy", null)
then I got date time in format (mm/dd/yyyy) : 10/20/2012 12:00:00 AM
But I need it should be converted in yyyy/mm/dd format. Please help me in this regard.

You should try this
DateTime.ParseExact("20-Oct-2012", "dd-MMM-yyyy", null).ToString("yyyy/mm/dd")
For further reading on formats Check This

You need to distinguish between two separate concerns: that of parsing your original string into an abstract DateTime representation, and that of converting the latter back into another string representation.
In your code, you're only tackling the former, and relying on the implicit ToString() method call (which uses the system's current locale) to convert it back to string. If you want to control the output format, you need to specify it explicitly:
// Convert from string in "dd-MMM-yyyy" format to DateTime.
DateTime dt = DateTime.ParseExact("20-Oct-2012", "dd-MMM-yyyy", null);
// Convert from DateTime to string in "yyyy/MM/dd" format.
string str = dt.ToString("yyyy/MM/dd");
Also note that the mm format specifier represents minutes; months are represented by MM.
Edit: 'Converted date contain value "10/20/2012 12:00:00 AM".' Be careful what you mean by that. The constructed DateTime value contains an abstract representation of the parsed date and time that is independent of any format.
However, in order to display it, you need to convert it back into some string representation. When you view the variable in the debugger (as you're presumably doing), Visual Studio automatically calls the parameterless ToString() method on the DateTime, which renders the date and time under the current culture (which, in your case, assumes the US culture).
To alter this behaviour such that it renders the date and time under a custom format, you need to explicitly call the ToString(string) overload (or one of the other overloads), as I've shown in the example above.

You could try this instead :
Convert.ToDateTime("20-Oct-2012").ToString("yyyy/MM/dd")
Hope this will help !!

DateTime formats C#

I have a string which needs to be converted and validated to a DateTime. The string is in the following format 'dd.mm.yy'
I am trying to convert it to DateTime using the following
string format = "dd.mm.yy";
date = DateTime.ParseExact(current.Substring(aiRule.AiLength), format,
CultureInfo.InvariantCulture);
but unfortunately this fails.
The question is how to convert a string in the format 'dd.mm.yy' to a DateTime ?
Thank you

mm means "minutes". I suspect you want "dd.MM.yy". See MSDN for more information about custom date and time format strings.
(In particular, read the part about the "yy" specifier and how it chooses which century to use. If you can possibly change the input to use a four digit year, that could save you some problems...)

the string format should be like this....
string Format = "dd.MM.yy"
mm is for showing minutes
MM is for showing months..
I hope it will helps you...

As earlier posts has already pointed out, mm means minutes and MM means months. I ran this test snippet and it works as expected:
string format = "dd.MM.yy";
string date = "27.10.11";
DateTime result;
result = DateTime.ParseExact(date, format, CultureInfo.InvariantCulture);

I'll tell something "heretical". If dd.MM.yy (with 2 or 4 yy) is the format of your local culture, then you could let the DateTime.Parse (not ParseExact!) do its work without setting it to CultureInfo.InvariantCulture, or perhaps setting it to your local culture like new CultureInfo("it-IT").