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DateTime.ToString from all formats to dd/MM/YYYY?

I have a simple routine which parses a DateTime.Now & performs a .ToString() on it to add it into a file name to be saved:
DateTime timeNow = DateTime.Now;
string dateNow = timeNow.ToShortDateString();
DateTime dateTime = DateTime.ParseExact(dateNow, "dd/MM/yyyy", CultureInfo.InvariantCulture);
string DateString = dateTime.ToString("dd-MMM-yy");
string fileName = string.Concat("MyArticle_" + region + "_" + DateString + fileExtension);
this is the resulting output string:
MyArticle_Africa_07-May-15.PNG
This is all good until I get a user on an American machine where the DateTime settings are different e.g.
05-07-15
In this case my ParseExact() method throws an exception as the input is not a valid date time. Is there a way to accommodate all date time inputs & parse to dd/MM/YYYY?

Actually, you don't need all these lines of code. You just need this:
// We just have to pass to the ToString
// method the exact format we want. Under the hood the CLR has
// the know how to execute this command and you get the desired
// output.
string DateString = DateTime.Now.ToString("dd-MMM-yy");
Furthermore, we use the DateTime.ParseExact method, when we want to get this exception you have mentioned. Saying this, I mean that we know that the string representation of dates, which we want to parse are of the exact format, we have specified in DateTime.ParseExact and if some of them aren't we wan't to be informed know it. Usually, we would have a try catch clause and in the catch clause we log this.

You need to try this:
string DateString = DateTime.Now.ToString("dd-MMM-yy");
string fileName = String.Concat("MyArticle_" + region + "_" + DateString + fileExtension);

You don't even need to convert DateTime.Now to a string, you can create the entire string in one step using String.Format :
var fileName = String.Format("MyArticle_{0}_{1:dd-MMM-yy}{2}",
region,DateTime.Now,fileExtension);
or
var fileName = String.Format(CurrentInfo.InvariantCulture,
"MyArticle_{0}_{1:dd-MMM-yy}{2}",
region,DateTime.Now,fileExtension);
to avoid internationalization issues.

MVC 4 - Force DateTime

Is it possible to force a DateTime object to use a different locale? I wish to populate a DateTime object with a UK DateTime but formatted as US.
I have tried the following:
DateTime ukDateTimeFormat = DateTime.Parse("10/26/2009 06:47", CultureInfo.GetCultureInfo("en-us"));
DateTime usDateTimeFormat = DateTime.Parse("26/10/2009 06:47", CultureInfo.GetCultureInfo("en-gb"));
string strDate = DateTime.Now.ToString(CultureInfo.InvariantCulture);
string[] dateString = strDate.Split('/');
DateTime enterDate = DateTime.Parse(dateString[0] + "/" + dateString[1] + "/" + dateString[2], CultureInfo.GetCultureInfo("en-us"));
Nothing works, I always end up with a UK formatted date.
Any help would be much appreciated :-)

It seems like you're confused between representing a date-time and formatting a date-time.
DateTime does not contain any format, it only represents the actual time. So the question about a US/UK format of a DateTime is meaningless.
If you want to display the time in a different format, that's not a DateTime, that's a string. You can use the various overloads of DateTime.ToString(...) in order to achieve different formatting as a string. There are some built-in formats, and you can specify a locale.

The DateTime object does not have an internal string format as such - your date is stored as a date and formatted on output. You can populate however you wish, however when outputting it, you'll need to specify your format, e.g.:
string formattedDate = ukDateFormat.ToString("MM/dd/yyyy HH:mm");

To format your date for the locale, use this code:
string formattedDate = ukDateFormat.ToString(System.Globalization.CultureInfo.CreateSpecificCulture("en-us"))

Save two TextBox as DateTime asp.net C#

I have two textBox in first i have Date in this format : 2012.09.20 and in the second i have Time in this format: 15:30:00. In database i have Column name "Eventstart" type: DateTime. Now i like to take the value from two textbox and put them in something like this:
DateTime end = Convert.ToDateTime(TextBoxEnd.Text) + Convert.ToDateTime(TextBoxTimeEnd.Text);
But give me this error : Error 2 Operator '+' cannot be applied to operands of type 'System.DateTime' and 'System.DateTime'

It sounds like you should be using:
DateTime date = Convert.ToDateTime(TextBoxEnd.Text);
DateTime time = Convert.ToDateTime(TextBoxTimeEnd.Text);
DateTime combined = date.Date + time.TimeOfDay;
Or you could combine the text and then parse that:
DateTime dateTime = Convert.ToDateTime(TextBoxEnd.Text + " " +
TextBoxTimeEnd.Text);
I'm not sure I'd use Convert.ToDateTime at all though - if you know the exact format that the textbox will be in, you should use DateTime.TryParseExact. You should work out which culture to use in that case though. If it's a genuinely fixed precise format, CultureInfo.InvariantCulture might be appropriate. If it's a culture-specific format, then use the user's culture.
You might also want to use an alternative UI representation which doesn't use textboxes at all, which would avoid potentially troubling string conversions.

Concatenate your TextBoxes text and use DateTime.ParseExact with format "yyyy.MM.dd HH:mm:ss"
After concatenating the text you should have: "2012.09.20 15:30:00"
DateTime dt = DateTime.ParseExact(TextBoxEnd.Text + " " + TextBoxTimeEnd.Text,
"yyyy.MM.dd HH:mm:ss",
CultureInfo.InvariantCulture);

Have you tried something like
DateTime end = Convert.ToDateTime(TextBoxEnd.Text) + TimeSpan.Parse(TextBoxTimeEnd.Text);

First concatenate both the values and then add it to a DateTime variable
example:
string str = date.Text + time.Text; // assumed date and time are textboxes
DateTime dt=new DateTime();
DateTime.TryParse(str,dt); // returns datetime in dt if it is valid

Datetime conversion in C# - using formats

I need to convert a String to DateTime format, for this I just tried like
DateTime.ParseExact(DateOfBirth,"MM/dd/yyyy",CultureInfo.InvariantCulture);
it's working fine when I pass the value like 05/30/2012.
But if I try to pass the value as 5/30/2012 its showing error:
String was not recognized as a valid DateTime
To fix this I tried like
DateTime.ParseExact(String.Format("{0:MM/dd/yyyy}", DateOfBirth), "MM/dd/yyyy",
CultureInfo.InvariantCulture);
it's still not working. Here If I try String.Format("{0:MM/dd/yyyy}", DateOfBirth) for the value 5/30/2012 its showing the same format instead of 05/30/2012.
How can I fix this, can anyone help me here...
check this link
string to DateTime conversion in C#

Use M/d/yyyy instead of the format specifier you're using. Using only a single M matches months with leading zeros as well. This is also true for d.

assuming your DateOfBirth string is always separated by slashes, you could try something like this:
string[] dateParts = DateOfBirth.Split('/');
DateTime.ParseExact(string.Format("{0:00}", dateParts[0]) + "/" + string.Format("{0:00}", dateParts[1]) + "/" + string.Format("{0:0000}", dateParts[2]));
I think the issue is the format string can't be recognized since DateOfBirth is not a DateTime object. Thus, you enforce formatting by reformatting the string yourself

There is an overload which might be of your interest
DateTime.ParseExact(DateOfBirth,
new[] { "MM/dd/yyyy", "M/dd/yyyy" },
CultureInfo.InvariantCulture,
DateTimeStyles.None);
This should help you take care of single as well as two digit month part (since 5 is failing for you as the format is MM)

Since you have separators in your string (ie /), you can just do;
DateTime.ParseExact(DateOfBirth,"M/d/yyyy",CultureInfo.InvariantCulture);
That will parse either single or double digit days/months. When you use MM/dd/yyyy, you're requiring them both to be double digit numbers, and that's obviously not what you want in this case.

Try just "d" instead of "MM/dd/yyyy".
So, the statement should be:
var date = DateTime.ParseExact(DateOfBirth, "d", CultureInfo.InvariantCulture);
The documentation for this is here:
http://msdn.microsoft.com/en-us/library/w2sa9yss.aspx
Edit
Oops, I misread the documentation. It should be "M/d/yyyy".

In case you need to make it culture-independent..
var dateTimeFormat = CultureInfo.CreateSpecificCulture(CultureInfo.CurrentUICulture.Name).DateTimeFormat;
dateTimeFormat.ShortDatePattern =
Regex.Replace(Regex.Replace(dateTimeFormat.ShortDatePattern, "[M]+", "MM"), "[d]+", "dd");
var newDate = date.HasValue ? date.Value.DateTime.ToString("d", dateTimeFormat) : null;

exception thrown "String was not recognized as a valid DateTime" what to do?

This is my code.but value cannot inserted in database. it takes system datetime except selected value by drop down list.
string strDateOfBirth = ddlMonth.SelectedValue.ToString();
strDateOfBirth = strDateOfBirth + "/" + ddlBirthDate.SelectedValue.ToString();
strDateOfBirth = strDateOfBirth + "/" + ddlYear.SelectedValue.ToString();
//objVivah.BirthDate = DateTime.ParseExact(strDateOfBirth, "MM/dd/yyyy hh:mm", null);
objVivah.BirthDate = Convert.ToDateTime(strDateOfBirth);
// objVivah.BirthDate = Convert.ToString(strDateOfBirth);

To convert a String to a DateTime using the Convert.ToDateTime function, the String must be in a specific format. If your String has a different format you need to convert it using DateTime.ParseExact function:
DateTime.ParseExact(strDateOfBirth, "MM/d/yyyy", CultureInfo.InvariantCulture);

Try this:
objVivah.BirthDate = DateTime.ParseExact(strDateOfBirth, "MM/dd/yyyy", null);
You might want to have a look at TryParse as well.

Well, I wouldn't create the string to start with - if you already have each part, you can parse those as integers (using int.Parse) and then create a DateTime from that. Or for the drop-down lists, you may be able to avoid even having the string value to start with, which would be ideal. (Make the value associated with each item just an integer. This may not be feasible depending on what UI technology you're using - you haven't said whether it's WinForms, ASP.NET, WPF etc.)
Using DateTime.ParseExact with an appropriate format string is the second best way to go, but I don't see any point in creating a string only to then parse it.