C＃中的日期时间

Question

In C# if I want to parse a datetime, but some times I just have either a date and not a time component or no date but a time component, how would I do this? Usualy when you leave out the time component, it automaticly assumes that the time is 12:00AM. But I don't want this. If the time component is missing then I just want the DateTime to store a date only and the leave the time component off.

Answer 1

内部DateTime的值只是一个UInt64 （C＃中的ulong ），它存储了自上一个日期以来的刻度数，因此无论您是否喜欢，时间组件将始终存在。

Answer 2

If you only need to display certain parts, just use any of the format strings (examples are for "en-us" culture):

DateTime.Now.ToString("d"); // 5/26/2009
DateTime.Now.ToString("t"); // 4:56 PM

The complete reference: http://msdn.microsoft.com/en-us/library/az4se3k1.aspx

Answer 3

It's not possible to have a DateTime without a time component. You could store a boolean flag along with it in a struct to store data about existence of that component. However, there's no way to use the automatic parsing routine to distinguish between a DateTime string with a time specified as 12:00 PM and a nonexistent one.

Answer 4

如果它真的让你烦恼，你总是可以创建一个包装类来隐藏datetime类的时间部分。

Answer 5

No you will have the time component no matter what. The best you can do is access the Date property on your DateTime object if you really have to.

http://msdn.microsoft.com/en-us/library/system.datetime.date.aspx

Answer 6

DateTime by definition stores a date and a time such that it cannot just represent one of them without representing the other. If you only want the date (or only the time), parse out the information you need and discard the rest of it.

Answer 7

As mentioned before DateTime will always have a Date and a Time part of it if you only want a single part use the way described by the others

DateTime date = DateTime.Parse("2009-11-30);
date.Year; = 2009
date.Month; = 11
date.Day; = 30
date.Hour; = 0
and so on

The thing you must be aware is that all of these methods will only return an integer.

If you want to know all the possible ways to parse a string John Sheehan has put together a great Cheat Sheet wit all possible ways to parse and manipulate dates , and other strings for that matter.

Answer 8

您可以拥有一个存储DateTime的类，并确定是否设置了时间，或者是否只设置了日期并相应地返回值。

Answer 9

A DateTime object is always stores a date + a time, not just one. You can always choose to work only with the date part, ie only use properties like Year, Month, DayOfWeek. But underneath there will aways be some stored time.

Answer 10

Use

DateTime date = new DateTime();
date = DateTime.Parse("1/1/2001"); 

to set the date, then use

date.ToShortDateString();

or

date.Year;
date.Month;
date.Day;

to get what you need. Hope that helps!

Answer 11

It is very dangerous to assume that the date portion of a DateTime is necessarily the date you are expecting. As pointed-out, DateTime always includes and considers the time aspect, even when you don't see it.

This is a big problem when you have data stored in different time-zones (and particularly if knowledge of that offset is not also kept, because it is assumed that what is being stored is a Date, not a date-with-time).

You may store a birthdate as '01/01/2000 00:00:00' during Summer-Time, which then is stored in UCT as '31/12/1999 23:00:00'. When you then read that birth-date later, the date portion is now a day early.

Best to create your own type. Strange that Microsoft didn't think it worth having a Date type.