Difference between revisions of "Working with Dates and Times in C Sharp"

Revision as of 17:38, 4 June 2009

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It is a rare application that can be developed without in some way needing to work with dates and times. In recognition of this fact, the Microsoft engineers responsible for C# gave us the DateTime object. In this chapter we will look in detail at using this object to work with dates and times in C# based applications. Topics covered include adding and subtracting time, getting the system date and time and formatting and extracting elements of dates and times in C#.

Creating a C# Date Time Object

The first step in using the DateTime object when working with dates and times in C# is to create an object instance. This may achieved using the new keyword passing through year, month and day values. For example, to create a DateTime object preset to September 22, 2008 the following code would need to be written:

using System;

class TimeDemo
{
       static void Main()
       {
	    DateTime meetingAppt = new DateTime(2008, 9, 22);
            System.Console.WriteLine (meetingAppt.ToString());
       }
}

In the above example, after setting the date we use the ToString() method of the DateTime object to output the current date and time value as a string.

It is important to note that if a time is not specified along with the date, the DateTime class constructor will set the time to 12:00am. With this in mind, the above code will output the following text:

9/22/2008 12:00:00 AM

Time values are specified by passing through hours, minutes and seconds values to the constructor. For example, to set the time to 14:30:00:

using System;

class TimeDemo
{
       static void Main()
       {
	    DateTime meetingAppt = new DateTime(2008, 9, 22, 14, 30, 0);
            System.Console.WriteLine (meetingAppt.ToString());
       }
}

Resulting in generation of the following output:

9/22/2008 2:30:00 PM

Getting the Current System Time and Date

The system date and time of the computer on which the C# code is executing may be accessed using the Today and Now static properties of the DateTime class. The Today property will return the current system date (and also the time set to 12:00 AM) whilst the Now property returns the current date and time.

For example:

using System;

class TimeDemo
{
       static void Main()
       {

            System.Console.WriteLine (DateTime.Today.ToString()

            System.Console.WriteLine (DateTime.Now.ToString());
       }
}

Adding or Subtracting from Dates and Times

The C# DateTime object provides a number of methods for adding or subtracting date and times from a DateTime object instance. These methods are outlined the following table:

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A key issue to understand is that these methods do not change the value of the DateTime object on which the method is called, but rather return a new DateTime object primed with the modified date and time. For example, to add 5 days to our example:

using System;

class TimeDemo
{
       static void Main()
       {
	    DateTime meetingAppt = new DateTime(2008, 9, 22, 14, 30, 0);
            DateTime newAppt = meetingAppt.AddDays(5);
            System.Console.WriteLine (newAppt.ToString());
       }
}

The above code will generate the following output, showing a date 5 days into the future from our original date and time:

9/27/2008 14:30:00 PM

To subtract from a date and time simply pass through a negative value to the appropriate method. For example, to subtract 10 months from our example object:

using System;

class TimeDemo
{
       static void Main()
       {
	    DateTime meetingAppt = new DateTime(2008, 9, 22, 14, 30, 0);
            DateTime newAppt = meetingAppt.AddMonths(-10);
            System.Console.WriteLine (newAppt.ToString());
       }
}

Resulting in the following output:

11/22/2007 2:30:00 PM

Retrieving Parts of a Date and Time

Dates and times are comprised of distinct and separate values, namely the day, month, year, hours, minutes, seconds and milliseconds. The C# DateTime object stores each of these values as a separate property within the object, allowing each to be accessed individually. The following code sample extracts each value and displays it in the console window:

using System;

class TimeDemo
{
       static void Main()
       {
	    DateTime meetingAppt = new DateTime(2008, 9, 22, 14, 30, 0);

            System.Console.WriteLine (meetingAppt.Day);
            System.Console.WriteLine (meetingAppt.Month);
            System.Console.WriteLine (meetingAppt.Year);
            System.Console.WriteLine (meetingAppt.Hour);
            System.Console.WriteLine (meetingAppt.Minute);
            System.Console.WriteLine (meetingAppt.Second);
            System.Console.WriteLine (meetingAppt.Millisecond);
       }
}

When compiled and executed, the above code will generate the following output:

22
9
2008
14
30
0
0

Formatting Dates and Times in C#

There are number of techniques available for extracting and displaying dates and times in particular formats. Output may be configured using a small number of predefined formatting methods or customized with an almost infinite number of variations using the ToString() method.

The basic formatting methods operate as follows:

  DateTime meetingAppt = new DateTime(2008, 9, 22, 14, 30, 0);

  System.Console.WriteLine(meetingAppt.ToLongDateString());   // Monday, September 22, 2008
  System.Console.WriteLine(meetingAppt.ToShortDateString());  // 9/22/2008
  System.Console.WriteLine(meetingAppt.ToShortTimeString());  // 2:30 PM

If the above prepackaged formatting methods do not provide the required output, a formidable variety of custom formats may be constructing using the ToString() method. The ToString() method takes as an argument a format string which specifies precisely how the date and time is to be displayed. The following example shows a few of this formats in action. The subsequent table lists all the possible format variables which may be used:

   DateTime meetingAppt = new DateTime(2008, 9, 22, 14, 30, 0);

   System.Console.WriteLine(meetingAppt.ToString("MM/dd/yy")); // 09/22/08

   System.Console.WriteLine(meetingAppt.ToString("MM - dd - yyyy")); // 09 - 22 - 2008

   System.Console.WriteLine(meetingAppt.ToString("ddd dd MMM yyyy")); // Mon 22 Sep 2008

   System.Console.WriteLine(meetingAppt.ToString("dddd dd MMMM yyyy")); // Monday September 22 2008

The full list of format patterns support by the ToString() method of the C# DateTime class is as follows:

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