DateTime string parsing

问题

I have made a generic parser for parsing ascii files. When I want to parse dates, I use ParseExact function in DateTime object to parse, but I get problems with the year.

The text to parse is i.e. "090812" with the parseExact string "yyMMdd".

I'm hoping to get a DateTime object saying "12/8-2009", but I get "12/8-1909". I know, that I could make an ugly solution by parsing it afterwards, and thereby modifying the year..

Anyone know of a smart way to solve this ??

Thanks in advance..

Søren

回答1:

Theoretically elegant way of doing this: change the TwoDigitYearMax property of the Calendar used by the DateTimeFormatInfo you're using to parse the text. For instance:

CultureInfo current = CultureInfo.CurrentCulture;
DateTimeFormatInfo dtfi = (DateTimeFormatInfo) current.DateTimeFormat.Clone();
// I'm not *sure* whether this is necessary
dtfi.Calendar = (Calendar) dtfi.Calendar.Clone();
dtfi.Calendar.TwoDigitYearMax = 1910;

Then use dtfi in your call to DateTime.ParseExact.

Practical way of doing this: add "20" to the start of your input, and parse with "yyyyMMdd".

回答2:

Well, if you're definite that all your source dates are this century, then you could use parseExact against a "20"-prefixed source string.

回答3:

You will need to determine some kind of threshold date appropriate for your data. If the parsed date is before this date, add 100 years. A safe way to do that is to prefix the input string with the appropriate century. In this example I've chosen 1970 as the cutoff:

string input = ...;
DateTime myDate;

if (Convert.ToInt32(input.Substring(0, 2)) < 70)
    myDate = DateTime.ParseExact("20" + input, ...);
else
    myDate = DateTime.ParseExact("19" + input, ...); 

Jon Skeet also posted a nice example using DateTimeFormatInfo that I had momentarily forgotten about :)

来源：https://stackoverflow.com/questions/1277320/datetime-string-parsing