VB.NET DateTime Examples
Represent dates with the DateTime type. Access DateTime constructors and properties.
DateTime. This Structure represents a point in time. It stores times, like 12 AM, and dates like yesterday. With TimeSpan we capture time differences.
TimeSpan 
Features. Methods are used to compute relative times such as yesterday and tomorrow. DateTime can be formatted—this changes it to a String.
Format
New instance. A DateTime instance can be created with the New operator. There are many overloads. But the overload shown here accepts 3 arguments.
Part A: The arguments here are the year, the month, and the day of that month. The value 2 stands for February.
Part B: Here we access the Year property on the DateTime instance we just created.
Warning: If you pass an invalid argument (one that no date could have), you will get an ArgumentOutOfRangeException.
VB.NET program that uses constructor
Module Module1
Sub Main()
' Part A: create new instance.
Dim value As DateTime = New DateTime(2017, 2, 1)
Console.WriteLine(value)
' Part B: test the year.
If value.Year = 2017 Then
Console.WriteLine("Year is 2017")
End If
End Sub
End Module
Output
2/1/2017 12:00:00 AM
Year is 2017
Yesterday. To get yesterday, we can access the Today property and then add negative one days to it. This is equivalent to subtracting one day from the DateTime instance.
VB.NET program that computes yesterday
Module Module1
Sub Main()
' Write the today value.
Console.WriteLine("Today: {0}", DateTime.Today)
' Subtract one day.
Dim yesterday As DateTime = DateTime.Today.AddDays(-1)
' Write the yesterday value.
Console.WriteLine("Yesterday: {0}", yesterday)
End Sub
End Module
Output
Today: 1/17/2010 12:00:00 AM
Yesterday: 1/16/2010 12:00:00 AM
Tomorrow. This is a good day to schedule less pleasurable tasks. To compute tomorrow, we add one day with Add Days() on the value returned by the Today property.
Note: The output of the program will be different depending on when you run it.
VB.NET program that computes tomorrow
Module Module1
Sub Main()
' Write Today.
Console.WriteLine("Today: {0}", DateTime.Today)
' Add one to Today to get tomorrow.
Dim tomorrow As DateTime = DateTime.Today.AddDays(1)
' Write.
Console.WriteLine("Tomorrow: {0}", tomorrow)
End Sub
End Module
Output
Today: 1/17/2010 12:00:00 AM
Tomorrow: 1/18/2010 12:00:00 AM
First day. Getting the first day in a year is useful. We defines two new methods to get the first day in a year. When no argument is specified, the current year (for Today) is used.
VB.NET program that finds first day
Module Module1
Sub Main()
' Write first day of current year.
Console.WriteLine("First day: {0}", FirstDayOfYear)
' Write first day of 1999.
Dim y As New DateTime(1999, 6, 1)
Console.WriteLine("First day of 1999: {0}", FirstDayOfYear(y))
End Sub
''' <summary>
''' Get first day of the current year.
''' </summary>
Private Function FirstDayOfYear() As DateTime
Return FirstDayOfYear(DateTime.Today)
End Function
''' <summary>
''' Get first day of the specified year.
''' </summary>
Private Function FirstDayOfYear(ByVal y As DateTime) As DateTime
Return New DateTime(y.Year, 1, 1)
End Function
End Module
Output
First day: 1/1/2010 12:00:00 AM
First day of 1999: 1/1/1999 12:00:00 AM
Last day. Here we compute the last day in a year. This may help with year-based record keeping. The method gets the first day of the next year, and then subtracts one day.
Tip: Please see also the IsLeapYear Function, which can tell us whether an additional day is in the year or not.
VB.NET program that computes last day
Module Module1
Sub Main()
' Write current last day.
Console.WriteLine("Last day: {0}", LastDayOfYear)
' Write last day of 1999.
Dim d As New DateTime(1999, 6, 1)
Console.WriteLine("Last day of 1999: {0}", LastDayOfYear(d))
End Sub
''' <summary>
''' Get last day of the current year.
''' </summary>
Private Function LastDayOfYear() As DateTime
Return LastDayOfYear(DateTime.Today)
End Function
''' <summary>
''' Get last day of the specified year.
''' </summary>
Private Function LastDayOfYear(ByVal d As DateTime) As DateTime
Dim time As New DateTime((d.Year + 1), 1, 1)
Return time.AddDays(-1)
End Function
End Module
Output
Last day: 12/31/2010 12:00:00 AM
Last day of 1999: 12/31/1999 12:00:00 AM
DaysInMonth. Months contain different numbers of days. With the shared DaysInMonth Function, we get day-counts for a month in a specific year. The 2 means February.
VB.NET program that uses DaysInMonth
Module Module1
Sub Main()
' There are 28 days in February.
Dim count As Integer = DateTime.DaysInMonth(2014, 2)
Console.WriteLine(count)
' Count days in March of 2014.
Dim count2 As Integer = DateTime.DaysInMonth(2014, 3)
Console.WriteLine(count2)
End Sub
End Module
Output
28
31
Get DayOfWeek. Every day in the future of our universe will have a day of week—like Monday or Tuesday. If you have a special day you need to test for, use the DayOfWeek property.
Info: This property returns a DayOfWeek Enum value. We can test it against a DayOfWeek enumerated constant.
Enum VB.NET program that gets day of week
Module Module1
Sub Main()
' Get current day of the week.
Dim day As DayOfWeek = DateTime.Today.DayOfWeek
' Write the current day.
Console.WriteLine("TODAY IS {0}", day)
End Sub
End Module
Output
TODAY IS Wednesday
DateString. This property, only offered in VB.NET, returns the current date in String representation. Usually, DateTime-based methods are preferable—they are more standard.
Internals: DateString simply accesses the Today property on DateTime, and then it calls ToString with a format string.
Tip: Many global functions in the VB.NET language are implemented with the standard .NET libraries.
VB.NET program that uses DateString
Module Module1
Sub Main()
Console.WriteLine(DateString)
End Sub
End Module
Output
05-18-2011
Date. This is another VB.NET special type. It aliases the DateTime type and has all the same methods. We can use Date interchangeably with DateTime.
Note: Usually DateTime is preferred in .NET programs as it is standard—all C# programs use DateTime not Date.
VB.NET program that uses Date type
Module Module1
Sub Main()
' The Date type is the same as the DateTime type.
Dim d As Date = New Date(2014, 10, 6)
Dim d2 As DateTime = New DateTime(2014, 10, 6)
If d = d2 Then
Console.WriteLine("Equal dates")
End If
End Sub
End Module
Output
Equal dates
DateTime.MinValue. Suppose we have a DateTime that we are not ready to assign to an actual value. We can use a special constant like MinValue to mean the default, zero value.
Also: We can use a nullable DateTime to mean "no value is set." A nullable may be clearer for this use in programs.
VB.NET program that uses DateTime.MinValue
Module Module1
Sub Main()
Dim value As DateTime = DateTime.MinValue
Console.WriteLine("MINVALUE: {0}", value)
' Test for MinValue.
If value = DateTime.MinValue Then
Console.WriteLine("MIN VALUE IS SET")
End If
End Sub
End Module
Output
MINVALUE: 1/1/0001 12:00:00 AM
MIN VALUE IS SET
Error, un-representable. We cannot create a DateTime that cannot possibly exist. Here we try to use a month of 20 in the constructor, but get an "un-representable" error.
Exception VB.NET program that shows parameter error
Module Module1
Sub Main()
' Cannot have a month of 20, no such month exists.
Dim value As DateTime = New DateTime(2000, 20, 1)
End Sub
End Module
Output
Unhandled Exception: System.ArgumentOutOfRangeException:
Year, Month, and Day parameters describe an un-representable DateTime.
at System.DateTime.DateToTicks(Int32 year, Int32 month, Int32 day)
at System.DateTime..ctor(Int32 year, Int32 month, Int32 day)...
Nothing. We cannot assign a DateTime to Nothing—we must use a special value like MinValue to mean "no date." But we can also use a Nullable DateTime.
Info: A Nullable type is a structure that wraps a value type like the DateTime. We can set a nullable DateTime to Nothing.
NullableIsNothing: In this program we set our nullable DateTime to nothing. And the IsNothing function recognizes our value is nothing.
Nothing VB.NET program that uses Nothing, DateTime
Module Module1
Sub Main()
' Use nullable DateTime.
Dim test As DateTime? = New DateTime(2000, 1, 1)
Console.WriteLine("GETVALUEORDEFAULT: {0}", test.GetValueOrDefault())
' The nullable DateTime can be Nothing.
test = Nothing
Console.WriteLine("ISNOTHING: {0}", IsNothing(test))
End Sub
End Module
Output
GETVALUEORDEFAULT: 1/1/2000 12:00:00 AM
ISNOTHING: True
Now property. This property is the same as Today, but it fills in the time. So it represents both the current time and the current date—Today just represents the current date.
DateTime.Now
Parse. DateTime.Parse converts a string to a DateTime. If we read in string data from user input or a database, we can parse it into a DateTime for further processing.
DateTime.Parse 
Timing. Timers are excellent for checking up on your program with a diagnostic method. They can execute any code. We can, for example, run a Timer every 30 seconds.
TimerStopwatchBenchmarks 
TimeZone. Day light changes, and time zones, can be complex. With the TimeZone.CurrentTimeZone property we access information that can help some programs.
TimeZone 
DateTime, file names. We can use a DateTime to generate a file name. This code can be used to write a daily log file from the result of some computation.
Filename, DateTime 
A summary. We used the DateTime type in the VB.NET language in some specific, useful ways. The examples provide a glimpse into the DateTime type but not a comprehensive view.
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