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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 ;-)

Change datetime to different culture

I have a datetime in this format "Wednesday, December 04, 2013". I want to translate it to different cultures at runtime so that i am able to store that in database according to culture.
This is my code:
dysMngmt.Day = curntDate.ToString("D");
The one line code above is getting the day.
So,please help me.

You can use the second argument of the ToString function, which enables you to pick a culture you see fit:
curntDate.ToString("D", CultureInfo.GetCultureInfo("en-US"))
As a side note, why are you saving the date in your database as a string? Why not use a native date date type? It will take less space and allow you comparisons etc., and then you'd just use the currect culture when reading it out of the database.

Unless you have a very good reason for handling the culture of each date seperatly within the application you should set this at the application level so that the default ToString() works with your intended culture.
http://support.microsoft.com/kb/306162
Also, you should probably also not store dates as text in your database.

Parse date when format is not constant c#

normally i parse date like this way
DateTime.Parse()
DateTime.ParseExact()
i am in situation where user run exe and pass date as argument. so user can give date with various format like
dd/MM/yyyy
MM/dd/yyyy
dd-MM-yyyy
MM-dd-yyyy
yyyyMMdd
so i have to parse that date. when date format is yyyyMMdd then i am parisng date like this way DateTime.ParseExact(this.enddate, "yyyyMMdd", CultureInfo.InvariantCulture).ToString("yyyy-MM-dd");
so guide me what code i should write to parse date which work for any date format. thanks

I would recommend that you standardize on a single format. Otherwise you will run into ambiguous dates in cases where you have dates that can be parsed by different formats, but represent different dates in both
Ex:
dd-MM-yyyy
MM-dd-yyyy

what code i should write to parse date which work for any date format
As a technical answer, you can pass multiple formats to DateTime.TryParseExact() via a string array containing all acceptable formats.
Practically, though, the others have already pointed out that there is no way to tell the difference between months and days when the format isn't strictly enforced.
One possible solution is to have the user pass the date in as three separate arguments, each flagged with some kind of indicator such as /y2013 /m11 /d12 or maybe y:2013 m:11 d:12. You can even mash them together like /y2013/m11/d12. Then you can use Regular Expressions to parse out the parts, or even just plain old string manipulation.

There's no built in way to parse dates which work for ANY format. However, you can quite easily define your own format using DateTimeFormatInfo, letting you convert more or less any format to a proper date, as long as you know the format ahead of time.

In every major website you enter the date using comboboxes for day/month/year
or some datetime widget. So I don't see a reason to use a textbox. If you really
need to, add a tooltip or a watermark with the predefined format and force the
user to it.

convert system date to M/d/yyyy format irrespective of system format using C#

How can I get today's date in M/d/yyyy format irrespective of system format of date using C#?
DateTime.Now.Tostring('M/d/yyyy')
is working only if the system date is in format dd/MM/yyyy or M/dd/yyyy but is not working in case yyyy-MM-dd format.
Eg:
if system date is 2013-06-26 then DateTime.Now.Tostring('M/d/yyyy') is converting the date into 06-26-2013 but not in 06/26/2013

Use CultureInfo.InvariantCulture to enforce / as date separator:
DateTime.Now.ToString("M/d/yyyy", CultureInfo.InvariantCulture)
Ideone

Looks like you just need to use CultureInfo.InvariantCulture as a second parameter in your .ToString method.
Console.WriteLine(DateTime.Now.ToString("M/d/yyyy", CultureInfo.InvariantCulture));

Using the invariant culture is the correct solution if you always want the same DateTime to produce the exact same string on multiple systems (or even on the same system due to culture changes). However, be aware that if this is user-visible, you're giving up the possibility of internationalization (for instance, if you display day or month names, they will be in English regardless of what language the user speaks). To only ensure that slashes are not replaced with another date separator, use single quotation marks:
DateTime.Now.Tostring("M'/'d'/'yyyy");
Edit:
Also, if your users are using different date formats, there's a good chance they're also using different time zones. If this DateTime needs to make sense across multiple systems, consider using DateTime.UtcNow. This will also protect you against potential bugs due to a user changing their time zone (when travelling, say) or daylight saving/summer time beginning/ending. If you're just displaying the string to the user at the current instance and not persisting it, DateTime.Now is probably what you want. In that case, however, I'd question why you're trying to mess with the format they've chosen.

Like this:
DateTime.Now.Tostring("M'/'d'/'yyyy");
The apostrofe forces the ToString() method to use the delimiter that you specified.
However, I would let the user choose a culture and use that cultures default formatting instead.

String.Format and culture

When formatting a string as opposed to a DateTime, does the culture ever come into play? Are there any examples of strings that would be formatted differently with two different cultures?

I don't believe so in the current Framework. But if Microsoft ever implements this suggestion on the Connect feedback site, it includes a suggestion to have a format specifier to force upper case:
String.Format("{0:U}", "SomeString") => "SOMESTRING"
Such formatting would be culture-specific.

If you are displaying a string that is stored as a resource it will make a difference if you have separate strings for different cultures (you'd use CultureInfo.CurrentUICulture). For example error messages accessed via a ResourceManager.

String.Format("{0}", "This string") - which I believe is what you're implying by your question, is not affected by the culture.

There are many scenarios when you need culture based formatting.
For example: - Number Format
5.25 in English is written as 5,25 in French
So, if you want to display French formatted number in your program which is in English culture the culture based string format comes into action.