DateTime ToString issue with formatting months with "mm" specifier

Question

I have a problem to get the correct format. I am expecting "2013/10", but instead I get "2013/00".

Why is that, and how can I fix this?

DateTime dt = DateTime.Parse("2013-Oct-01");   
string str2 = dt.ToString("yyyy/mm");

Answer 1

mm is for minute while MM is for month.

DateTime dt = DateTime.Parse("2013-Oct-01");
string str2 = dt.ToString("yyyy/MM");

See MSDN article DateTime.ToString méthode (String).

For a more complete list:

// Create date time 2008-03-09 16:05:07.123
DateTime dt = new DateTime(2008, 3, 9, 16, 5, 7, 123);

String.Format("{0:y yy yyy yyyy}", dt);  // "8 08 008 2008"   year
String.Format("{0:M MM MMM MMMM}", dt);  // "3 03 Mar March"  month
String.Format("{0:d dd ddd dddd}", dt);  // "9 09 Sun Sunday" day
String.Format("{0:h hh H HH}",     dt);  // "4 04 16 16"      hour 12/24
String.Format("{0:m mm}",          dt);  // "5 05"            minute
String.Format("{0:s ss}",          dt);  // "7 07"            second
String.Format("{0:f ff fff ffff}", dt);  // "1 12 123 1230"   sec.fraction
String.Format("{0:F FF FFF FFFF}", dt);  // "1 12 123 123"    without zeroes
String.Format("{0:t tt}",          dt);  // "P PM"            A.M. or P.M.
String.Format("{0:z zz zzz}",      dt);  // "-6 -06 -06:00"   time zone

Answer 2

mm is minutes. You need to use MM which is months:

var str2 = dt.ToString("yyyy/MM");