Working with Dates and Times in C Sharp

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.

Contents

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

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:

Method	Description
Add	Adds/Subtracts the value of the specified TimeSpan object instance.
AddDays	Adds/Subtracts the specified number of days
AddHours	Adds/Subtracts the specified number of hours
AddMilliseconds	Adds/Subtracts the specified number of Milliseconds
AddMinutes	Adds/Subtracts the specified number of minutes
AddMonths	Adds/Subtracts the specified number of months
AddSeconds	Adds/Subtracts the specified number of seconds
AddYears	Adds/Subtracts the specified number of years

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