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DateTime.TryParseExact Parses date value but adds default time value (where there was none)

edit: since I've had so many comments regarding utilising TryParseExact with a single format instead of an array:
I must test all of the formats within the array - the inputs can potentially be these formats, and my unit tests for these other formats actually work. I MUST use them all.
I am aware that DateTime.TryParse would match the first and not iterate further. Hence I am using TryParseExact as Microsoft shows. It should match exactly. BUT it doesn't work in this scenario.
TLDR: Given a string of the format "dd/MM/yyyy" with value "29/11/2019" DateTime.TryParseExact returns a match with the format "dd/MM/yyyy hh:mm tt" and value 29/11/2019 12:00 AM. Why?
Question: How can I ensure a string of the format "dd/MM/yyyy" returns as a match with the format "dd/MM/yyyy" instead of "dd/MM/yyyy hh:mm tt" when using TryParseExact?
The long explanation of Context;
I have the following problem. I need to parse multiple date formats from strings to datetime values. They (input strings) can appear in the following formats:
{ "dd/MM/yyyy hh:mm tt", "dd/M/yyyy hh:mm tt", "dd/MM/yyyy H:mm", "dd/MM/yyyy H:mm", "dd/MM/yyyy H:m", "dd/MM/yyyy", "dd-MM-yyyy", "d-M-yyyy", "dddd, d MMMM yyyy"};
To solve this, I wrote a string extension that parses a given input string and returns a bool success and a potential matching format.
private static readonly string[] _DateFormats = new string[] { "dd/MM/yyyy hh:mm tt", "dd/M/yyyy hh:mm tt", "dd/MM/yyyy H:mm", "dd/MM/yyyy H:mm", "dd/MM/yyyy H:m", "dd/MM/yyyy", "dd-MM-yyyy", "d-M-yyyy", "dddd, d MMMM yyyy"};
public static bool StringToDateTime(this string dateTimeString, out DateTime dateTimeValue, out string matchingFormat)
{
matchingFormat = ""; // defaults
dateTimeValue = new DateTime();
if (string.IsNullOrEmpty(dateTimeString)) return false;
foreach (string format in DateFormats)
{
matchingFormat = format;
if (DateTime.TryParseExact(dateTimeString, DateFormats, AUSCulture, DateTimeStyle, out dateTimeValue)) return true;
}
return false;
}
This returns the string input "29/11/2019 successfully" as the DateTime 29/11/2019 12:00 AM with the matching format as "dd/MM/yyyy hh:mm tt", rather than the format matching the original input 29/11/2019.
Given this issue, the only (duct-tape) solution I could think of is:
public static bool StringToDateTime(this string dateTimeString, out DateTime dateTimeValue, out string matchingFormat)
{
matchingFormat = ""; // defaults
dateTimeValue = new DateTime();
if (string.IsNullOrEmpty(dateTimeString)) return false;
foreach (string format in DateFormats)
{
matchingFormat = format;
if (DateTime.TryParseExact(dateTimeString, DateFormats, AUSCulture, DateTimeStyle, out dateTimeValue))
{
// ensure the datetime format is consistent with the dateTimeString passed to us.
if(dateTimeString.Length != matchingFormat.Length)
{
var _matchingFormat = DateFormats.First(d => d.Length == dateTimeString.Length);
matchingFormat = string.IsNullOrEmpty(_matchingFormat) ? matchingFormat : _matchingFormat;
}
return true;
}
}
return false;
}
Which works, but obviously, this has further issues (begetting the formatting of input, etc.). So I'd rather not use this.

System.DateTime cannot exist without the time component, so it's no possible to parse a date to DateTime and not the time component. It will default to the start of day e.g. 12:00 AM, which is the same result as calling dateTime.Date(). This will allow you to compare two dates without considering the time of day.
If having or storing the time element really bothers you then you can either create your own struct to store the date or consider using something like NodaTime that provides a date only struct.
Also, Dotnet 6 will introduce DateOnly and TimeOnly structs to do exactly this. You can read more about it on the MS devblogs.

You are passing the whole array of formats, so it will match any of them.
Since you are in a foreach over DateFormats, you only need to match against the current value.
So replace this line
if (DateTime.TryParseExact(dateTimeString, DateFormats, AUSCulture, DateTimeStyle, out dateTimeValue))
return true;
with this
if (DateTime.TryParseExact(dateTimeString, format, AUSCulture, DateTimeStyle, out dateTimeValue))
return true;

String to date conversion in c# as yyyy/mm/dd

I would like convert string content to date format as yyyy/MM/dd HH:mm:ss tt
string date = "2014-11-20 3:21:00 PM";
DateTime date_=System.DateTime.Now;
var result = DateTime.TryParseExact(date, "yyyy-MM-dd HH:mm:ss tt",
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None,
out date_);
But it returns result doesn't match requirement also TryParse function return false. If time zone is not defined, it will return expected result.

HH specifier is for 24 hour clock which is 00 to 23.
You need to use h specifier instead which represents 1 to 12 in 12 hour clock.
Also you don't need to initialize your out parameter value. Definition will be enough like;
string date = "2014-11-20 3:21:00 PM";
DateTime date_;
var result = DateTime.TryParseExact(date, "yyyy-MM-dd h:mm:ss tt",
CultureInfo.InvariantCulture,
DateTimeStyles.None, out date_);

The DateTime data type format is always MM/dd/yyyy hh:mm:ss tt (i.e. Date = {11/20/2014 12:00:00 AM}),
If you want to display the value you can change the format by using ToString extention method

Converting string to date time

I have a date which comes in a string like so:
09/25/2014 09:18:24
I need it like this (yyyy-mm-dd):
2014-09-25 09:18:24
The object that this date goes into is a nullable date.
Tried this does not work:
DateTime formattedDate;
bool result = DateTime.TryParseExact(modifiedDate, "yyyy-MM-dd",
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out formattedDate);
Any clues?
Thanks in advance.

From DateTime.TryParseExact
Converts the specified string representation of a date and time to its
DateTime equivalent. The format of the string representation must
match a specified format exactly.
In your case, they are not. Use yyyy-MM-dd HH:mm:ss format instead.
string s = "2014-09-25 09:18:24";
DateTime dt;
if(DateTime.TryParseExact(s, "yyyy-MM-dd HH:mm:ss",
CultureInfo.InvariantCulture,
DateTimeStyles.None, out dt))
{
Console.WriteLine(dt);
}
It is a little bit unclear but if your string is 09/25/2014 09:18:24, then you can use MM/dd/yyyy HH:mm:ss format instead. Just a tip, "/" custom format specifier has a special meaning as replace me with current culture or supplied culture date separator. That means, if your CurrentCulture or supplied culture's DateSeparator is not /, your parsing operation will fail even if your format and string matches exactly.
If you have already a DateTime and you want to format it, you can use DateTime.ToString(string) method like;
dt.ToString("yyyy-mm-dd", CultureInfo.InvariantCulture); // 2014-09-25
or
dt.ToString("yyyy-mm-dd HH:mm:ss", CultureInfo.InvariantCulture); // 2014-09-25 09:18:24
Remember, a DateTime does not have any implicit format. It just contains date and time values. String representations of them have formats.

In answer to your question, to convert it as you prefer, do it like this:
string originalDate = "09/25/2014 09:18:24";
DateTime formattedDate;
if (DateTime.TryParseExact(originalDate, "MM/dd/yyyy HH:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.None, out formattedDate))
{
string output = formattedDate.ToString("yyyy-mm-dd HH:mm:ss", CultureInfo.InvariantCulture);
}
And then output will have your desired format.

DateTime dateOf = Convert.ToDateTime("09/25/2014 09:18:24");
string myFormat = "yyyy-mm-dd";
string myDate = dateOf.ToString(myFormat); // output 2014-18-25
Datetime format

How to find exact format of a date string?

I need to know exact date format that will perse the string 16-Aug-78 12:00:00 AM. I have tried various string like "ss-MMM-yy hh:mm:ss". Is there any way for finding it to converting to any general format. I am using CultureInfo.InvariantCulture class.

Your string format is wrong. It has to match your string format exactly. You can use dd-MMM-yy hh:mm:ss tt format instead.
Here an example in LINQPad.
string s = "16-Aug-78 12:00:00 AM";
var date = DateTime.ParseExact(s, "dd-MMM-yy hh:mm:ss tt",
CultureInfo.InvariantCulture);
date.Dump();
Custom Date and Time Format Strings
Or, since dd-MMM-yy hh:mm:ss tt is a standart date and time format for InvariantCulture, you can directly DateTime.Parse method like;
string s = "16-Aug-78 12:00:00 AM";
var date = DateTime.Parse(s, CultureInfo.InvariantCulture);
date.Dump();
Here a demonstration.
Is there any way for finding it to converting to any general format?
There is no way to get format of a string except you create your own formatting. Only you can know what is your string format exactly, computer can't.
For example; 01/02/2014 can be 1 February 2014 or 2 January 2014 depends on which custom format you can parse it.

Try as below
var dstring = "16-Aug-78 12:00:00 AM";
DateTime result;
var matchingCulture = CultureInfo.GetCultures(CultureTypes.AllCultures).FirstOrDefault(ci => DateTime.TryParse(dstring, ci, DateTimeStyles.None, out result))

You have wrong format string, you are using ss for day it should be dd. This article Custom Date and Time Format Strings explains what you need for custom format.
Use
"dd-MMM-yy hh:mm:ss tt"
Instead of
"ss-MMM-yy hh:mm:ss"
You can use DateTime.ParseExact to parse the string.
DateTime dt = DateTime.ParseExact("16-Aug-78 12:00:00 AM", "dd-MMM-yy hh:mm:ss tt", CultureInfo.InvariantCulture, DateTimeStyles.None);

You can try with DateTime.TryParseExact():
string strDate = "16-Aug-78 12:00:00 AM";
DateTime datDate;
if(DateTime.TryParseExact(strDate , new string[] {"dd-MMM-yy hh:mm:ss tt" },
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None, out datDate))
{
Console.WriteLine(datDate);
}
else
{
Console.WriteLine("Error in datetime format");
}

String conversion to datetime independant of string format

I want to convert a string to datetime format.
The thing is that the string comes in different formats.
For instance, in the code below, strDate can be "2/20/2014 1:41:57 PM" or "20/02/2014 13:44:56".
Convert.ToDateTime(strDate) executes well just for one format (the one on the user browser settings) and generates an error for the other.
How can I successfully convert the string to datetime independently of the string format?
Thanks
DateTime dt = Convert.ToDateTime(strDate);

You can use DateTime.TryParseExact or Datetime.ParseExact with multiple formats like:
string dateStr = "20/02/2014 1:41:57 PM";
string[] dateFormats = new[]
{
"d/M/yyyy h:mm:ss tt",
"M/d/yyyy h:mm:ss tt",
};
DateTime dt;
if (DateTime.TryParseExact(dateStr,
dateFormats,
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out dt))
{
//valid dates for formats
}
else
{
//invalid date
}
the problem with this approach is that it would give you inconsistent results with strings like 10/02/2014 1:41:57 PM, The above code would parse it as 10th Feb 2014, not as October 2nd 2014, to avoid this you can customize your client side to return date in specific format and then parse accordingly.

you want DateTime.Parse() or DateTime.TryParse()
i.e.
DateTime dt;
if(DateTime.TryParse(stringDate, out dt)
{
//successful datetime conversion
}
if you know the string will be one of several exact formats, you can use DateTime.TryParseExact() and pass in a string array of each format (the second overload).