如何在c＃中将字符串转换为特定的DateTime格式？

Question

How to convert the string "28/09/2009" to DateTime in a specific format? Ex: I want to convert "2009-09-28 17:30:40" to DateTime. I want to convert "28/09/2009 17:30:40" to DateTime. I want to convert "20090928 17:30:40" to DateTime.

There are multiple possible formats. I tried this:

string[] formats = new string[] {"yyyymmdd","yyyymmddThhmmss","yyyy/mm/dd  hh:mm:ss","yyyy/mm/dd","yyyy-mm-dd hh:mm:ss","yyyy-mm-dd"};
IFormatProvider culture = new CultureInfo("en-US", true);
DateTime formattedDate = DateTime.ParseExact(aDate, formats, culture, DateTimeStyles.None);

This example throws an exception with the message "String was not recognized as a valid DateTime".

What's wrong in the code above?

Answer 1

None of your formats put the day first, like this: "dd/MM/yyyy" .

Also note the capital 'M', since lower case 'm' is for 'minutes'. You have a similar problem with your hours; since your samples all use 24 hour time you need a capital 'H'.

Your format string array should look like this:

string[] formats = {"dd/MM/yyyy", "yyyy-MM-dd HH:mm:ss", "dd/MM/yyyy HH:mm:ss", "yyyyMMdd HH:mm:ss"};

Those formats exactly match your supplied sample strings.

Additionally, you probably want to use the invariant culture rather than en-US in this case. Otherwise, the '/' character in your format strings is really a culture-specific date separator, which a user might over-ride on their local system.

Finally, since you're obviously having trouble matching up the strings up, you might want to use TryParseExact() , which works just like parse exact but uses an out parameter rather than returning the value, so that it can return a boolean to indicate success or failure rather than throwing an exception.

See the complete format string reference here:
http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx