C# : How to convert string to DateTime, where the string can have any of the standard datetime format

Question

I had posted a question on DateTime to String conversion, I got many satisfying answers for that .. so I thank StackOverflow very much ..
Here is one more problem of String manupulation, I am stuck with ..

I have to convert a string (from some external source) using C# code .. the string can have these expected format of DateTime ..

1. 02/31/2009 01:59:59 24 hours format
2. 02/31/2009 01:59:59 AM 12 hours format
3. 2/31/2009 1:59:59
4. 2/31/2009 1:59:59 AM
5. 02/01/2009 01:59:59 AM
6. 2/1/2009 1:59:59
   
7. and so on .......

I tried using DateTime(Convert.ToInt32(string_date.Substring(6,4)),Int,Int,Int,Int,Int,Int)
ie, By extracting the values of month, Day etc

But it doesn't work .. because I can't extract the values with substring perfectly .. as the length of string is Varying
I also have tried to extract the values referring the occurance of "/", " space " and ":" but it becomes bottle neck to derive with (non-)Occurrence of AM/PM

Only the length of Day, Month and Hours can vary ..

Answer 1

You can use the DateTime.ParseExact overload that takes a list of formats:

private static string[] formats = new string[]
    {
        "MM/dd/yyyy HH:mm:ss tt",
        "MM/dd/yyyy HH:mm:ss",
        "M/dd/yyyy H:mm:ss tt",
        "M/dd/yyyy H:mm:ss"        
    };

private static DateTime ParseDate(string input)
{
    return DateTime.ParseExact(input, formats, CultureInfo.InvariantCulture, DateTimeStyles.None);
}

This will throw a FormatException if the passed string does not match any of the given formats. Notice that the formats expecting AM/PM should appear before identical formats without AM/PM ( "MM/dd/yyyy HH:mm:ss tt" comes before "MM/dd/yyyy HH:mm:ss" ).

Update
As Henk points out in the comments, the same functionality is available when using TryParseExact which removes exception situation. Also, paired with nullable types this can be made a bit cleaner:

private static DateTime? ParseDate(string input)
{
    DateTime result;
    if (DateTime.TryParseExact(input, formats, CultureInfo.InvariantCulture, DateTimeStyles.None, out result))
    {
        return result;
    }
    return null;
}

Now it will simply return a null reference if it fails to parse the input.

Answer 2

Take a look at the TryParseExact method. Here's an example with the first case:

DateTime date;
// I changed 02/31/2009 to 01/31/2009 because the first is not a valid date
if (DateTime.TryParseExact("01/31/2009 01:59:59", "MM/dd/yyyy HH:mm:ss", null, DateTimeStyles.None, out date))
{
    // string successfully parsed => do something with the date
}

You could then keep a list of different formats and try to parse the string with all of them until you succeed.

Answer 3

Here are all the possible formats ..

1. MM/dd/yyyy 08/22/2006
2. dddd, dd MMMM yyyy Tuesday, 22 August 2006
3. dddd, dd MMMM yyyy HH:mm Tuesday, 22 August 2006 06:30
4. dddd, dd MMMM yyyy hh:mm tt Tuesday, 22 August 2006 06:30 AM
5. dddd, dd MMMM yyyy H:mm Tuesday, 22 August 2006 6:30
6. dddd, dd MMMM yyyy h:mm tt Tuesday, 22 August 2006 6:30 AM
7. dddd, dd MMMM yyyy HH:mm:ss Tuesday, 22 August 2006 06:30:07
8. MM/dd/yyyy HH:mm 08/22/2006 06:30
9. MM/dd/yyyy hh:mm tt 08/22/2006 06:30 AM
10. MM/dd/yyyy H:mm 08/22/2006 6:30
11. MM/dd/yyyy HH:mm:ss 08/22/2006 06:30:07
12. MMMM dd August 22
13. yyyy'-'MM'-'dd'T'HH':'mm':'ss.fffffffK 2006-08-22T06:30:07.7199222-04:00
14. ddd, dd MMM yyyy HH':'mm':'ss 'GMT' Tue, 22 Aug 2006 06:30:07 GMT
15. yyyy'-'MM'-'dd'T'HH':'mm':'ss 2006-08-22T06:30:07
16. HH:mm 06:30
17. hh:mm tt 06:30 AM
18. H:mm 6:30
19. h:mm tt 6:30 AM
20. HH:mm:ss 06:30:07
21. yyyy'-'MM'-'dd HH':'mm':'ss'Z' 2006-08-22 06:30:07Z
22. dddd, dd MMMM yyyy HH:mm:ss Tuesday, 22 August 2006 06:30:07
23. yyyy MMMM 2006 August

Answer 4

DateTime dt1 = DateTime.ParseExact("2007/01/01 04:23:12", "yyyy/MM/dd hh:mm:ss", System.Globalization.CultureInfo.CurrentCulture);

DateTime dt = Convert.ToDateTime("2007/01/01 04:23:12", System.Globalization.CultureInfo.CurrentCulture);

System.Globalization.CultureInfo.CurrentCulture format param