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

Revision as of 20:32, 19 February 2008

It is a rare application that can be developed without in some way needing to work with dates and times. In recongition of this fact, 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.

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

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:

An 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 distint and seperate values, namely the day, month, year, hours, minutes, seconds and milliseconds. The C# DateTime object stores each of these values is a separate property with 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

Basic Formatting and Dates and Times