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ParseExact with format "dMMyyyy" not recognizing date

I was looking in the Microsoft doc's and I can't find any explanation why ParseExact doesn't understand my date.
Could somebody explain why this code throws an exception?
DateTime.ParseExact("6092019", "dMMyyyy", CultureInfo.InvariantCulture, DateTimeStyles.None)

From the docs: DateTime.ParseExact Method
If format is a custom format pattern that does not include date or
time separators (such as "yyyyMMddHHmm"), use the invariant culture
for the provider parameter and the widest form of each custom format
specifier. For example, if you want to specify hours in the format
pattern, specify the wider form, "HH", instead of the narrower form,
"H".
So in your case you probably should use approach suggested in John's answer - add "missing" zero and parse with wider date format "dd"

The problem here seems to be that d can be a one-digit or two-digit date, so the parser struggles to determine if "2102019" refers to the 2nd of November 2019, or the 21st of... and then it breaks. With delimiters, the parser is able to act more intelligently. It will happily parse "2-10-2019" using "d-MM-yyyy".
My suggested solution to your problem is to pad the string, and change your format string:
string dateToParse = "6092019";
string paddedDateToParse = dateToParse?.PadLeft(8, '0'); // 06092019
DateTime parsedDate = DateTime.ParseExact(paddedDateToParse, "ddMMyyyy", CultureInfo.InvariantCulture, DateTimeStyles.None);
Try it online

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

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").

How to create a .NET DateTime from ISO 8601 format

I've found how to turn a DateTime into an ISO 8601 format, but nothing on how to do the reverse in C#.
I have 2010-08-20T15:00:00Z, and I want to turn it into a DateTime object.
I could separate the parts of the string myself, but that seems like a lot of work for something that is already an international standard.

This solution makes use of the DateTimeStyles enumeration, and it also works with Z.
DateTime d2 = DateTime.Parse("2010-08-20T15:00:00Z", null, System.Globalization.DateTimeStyles.RoundtripKind);
This prints the solution perfectly.

Although MSDN says that "s" and "o" formats reflect the standard, they seem to be able to parse only a limited subset of it. Especially it is a problem if the string contains time zone specification. (Neither it does for basic ISO8601 formats, or reduced precision formats - however this is not exactly your case.) That is why I make use of custom format strings when it comes to parsing ISO8601. Currently my preferred snippet is:
static readonly string[] formats = {
// Basic formats
"yyyyMMddTHHmmsszzz",
"yyyyMMddTHHmmsszz",
"yyyyMMddTHHmmssZ",
// Extended formats
"yyyy-MM-ddTHH:mm:sszzz",
"yyyy-MM-ddTHH:mm:sszz",
"yyyy-MM-ddTHH:mm:ssZ",
// All of the above with reduced accuracy
"yyyyMMddTHHmmzzz",
"yyyyMMddTHHmmzz",
"yyyyMMddTHHmmZ",
"yyyy-MM-ddTHH:mmzzz",
"yyyy-MM-ddTHH:mmzz",
"yyyy-MM-ddTHH:mmZ",
// Accuracy reduced to hours
"yyyyMMddTHHzzz",
"yyyyMMddTHHzz",
"yyyyMMddTHHZ",
"yyyy-MM-ddTHHzzz",
"yyyy-MM-ddTHHzz",
"yyyy-MM-ddTHHZ"
};
public static DateTime ParseISO8601String ( string str )
{
return DateTime.ParseExact ( str, formats,
CultureInfo.InvariantCulture, DateTimeStyles.None );
}
If you don't mind parsing TZ-less strings (I do), you can add an "s" line to greatly extend the number of covered format alterations.

using System.Globalization;
DateTime d;
DateTime.TryParseExact(
"2010-08-20T15:00:00",
"s",
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeUniversal, out d);

Here is one that works better for me (LINQPad version):
DateTime d;
DateTime.TryParseExact(
"2010-08-20T15:00:00Z",
#"yyyy-MM-dd\THH:mm:ss\Z",
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeUniversal,
out d);
d.ToString()
produces
true
8/20/2010 8:00:00 AM

It seems important to exactly match the format of the ISO string for TryParseExact to work. I guess Exact is Exact and this answer is obvious to most but anyway...
In my case, Reb.Cabin's answer doesn't work as I have a slightly different input as per my "value" below.
Value: 2012-08-10T14:00:00.000Z
There are some extra 000's in there for milliseconds and there may be more.
However if I add some .fff to the format as shown below, all is fine.
Format String: #"yyyy-MM-dd\THH:mm:ss.fff\Z"
In VS2010 Immediate Window:
DateTime.TryParseExact(value,#"yyyy-MM-dd\THH:mm:ss.fff\Z", CultureInfo.InvariantCulture,DateTimeStyles.AssumeUniversal, out d);
true
You may have to use DateTimeStyles.AssumeLocal as well depending upon what zone your time is for...

This works fine in LINQPad4:
Console.WriteLine(DateTime.Parse("2010-08-20T15:00:00Z"));
Console.WriteLine(DateTime.Parse("2010-08-20T15:00:00"));
Console.WriteLine(DateTime.Parse("2010-08-20 15:00:00"));

DateTime.ParseExact(...) allows you to tell the parser what each character represents.

parse iCalendar date using c#

Is there a direct way to parse an iCalendar date to .net using c#?
An iCalendar date looks like this:
2009-08-11T10:00+05:0000
I need to parse it to display it in a friendly format... thanks

string strDate = "2009-08-11T10:00+05:0000";
DateTimeFormatInfo dtfi = new DateTimeFormatInfo();
dtfi.FullDateTimePattern = "yyyy-MM-ddTHH:mmzzz";
DateTime dt = DateTime.Parse(c.Substring(0, c.Length-2), dtfi);
zzz is for time zone, but is only recognized when expressed like this: +xx:xx.
I tested with your example, removing the last 2 0's then parsing with a custom DateTimeFormatInfo works.

You can use DateTime.Parse() to parse everything before the +. I do not know the iCalendar format specification but I assume after the + is the hours/minutes to add to the date before the +. So you could then use AddHours() and AddMinutes() to add the required bits to the DateTime returned by DateTime.Parse().
This requires a bit of string parsing but with a bit of regex you should be fine...

Since this is not a standard format string, but you know the exact format, you can use DateTime.ParseExact and specify a custom format string, like this:
DateTime.ParseExact(d, "yyyy-MM-ddTHH:mmzzz00", CultureInfo.InvariantCulture);
The 'zzz' specifier represents the hours and minutes offset from UTC, and the two concluding zeros are just literals to match format with which you're dealing.