VB.NET DateTime Format
Use DateTime format patterns. Call the ToString method with a format string.
DateTime format. We format dates and times with a string pattern. Conceptually this is simple. In practice, there are details we must account for if we want a functional program.
Formatting DateTime as a string is straightforward. Often we use format patterns like "HH." But methods like ToShortDateString are also useful.
Example. First we get the current time through DateTime.Now. When you execute these code examples, the current DateTime will be different on your computer.
Here: A format string beginning with MMM (for the month) is used. Look at how the pattern matches up to the output of the program.
VB.NET program that uses format string with DateTime
Module Module1
Sub Main()
' Use current time.
' ... Use a format.
' ... Write to console.
Dim time As DateTime = DateTime.Now
Dim format As String = "MMM ddd d HH:mm yyyy"
Console.WriteLine(time.ToString(format))
End Sub
End Module
Output
Feb Tue 21 13:26 2017
Description of format
MMM Three-letter month.
ddd Three-letter day of the week.
d Day of the month.
HH Two-digit hours on 24-hour scale.
mm Two-digit minutes.
yyyy Four-digit year.
Pattern. It is possible to change the pattern used in the format string in many ways. To explore this, we try to shorten the output by changing the MMM to a single M.
Note: The pattern matches up to the output of the program. The description of the formatting string is shown in tabular format.
VB.NET program that uses different format string
Module Module1
Sub Main()
' Use current time.
' ... Use a format.
' ... Write to console.
Dim time As DateTime = DateTime.Now
Dim format As String = "M d HH:mm yy"
Console.WriteLine(time.ToString(format))
End Sub
End Module
Output
5 18 16:46 10
Description of format
M One-digit month number.
d One-digit day of the month.
HH Two-digit hours on 24-hour scale.
mm Two-digit minutes.
yy Two-digit year.
One-character formats. Here we use single-character format strings. For this feature, you pass a one-character string to the ToString function.
Note: This encodes a specific formatting style. Sometimes it might be worth memorizing the ones you like the most.
However: Searching for a formatting string table on the Internet is much easier and requires less effort.
VB.NET program that uses one-character formats
Module Module1
Sub Main()
' Acquire current time and then try format strings.
Dim now As DateTime = DateTime.Now
Console.WriteLine(now.ToString("d"))
Console.WriteLine(now.ToString("D"))
Console.WriteLine(now.ToString("f"))
Console.WriteLine(now.ToString("F"))
Console.WriteLine(now.ToString("g"))
Console.WriteLine(now.ToString("G"))
Console.WriteLine(now.ToString("m"))
Console.WriteLine(now.ToString("M"))
Console.WriteLine(now.ToString("o"))
Console.WriteLine(now.ToString("O"))
Console.WriteLine(now.ToString("s"))
Console.WriteLine(now.ToString("t"))
Console.WriteLine(now.ToString("T"))
Console.WriteLine(now.ToString("u"))
Console.WriteLine(now.ToString("U"))
Console.WriteLine(now.ToString("y"))
Console.WriteLine(now.ToString("Y"))
End Sub
End Module
Output
5/18/2010
Tuesday, May 18, 2010
Tuesday, May 18, 2010 4:47 PM
Tuesday, May 18, 2010 4:47:55 PM
5/18/2010 4:47 PM
5/18/2010 4:47:55 PM
May 18
May 18
2010-05-18T16:47:55.9620000-06:00
2010-05-18T16:47:55.9620000-06:00
2010-05-18T16:47:55
4:47 PM
4:47:55 PM
2010-05-18 16:47:55Z
Tuesday, May 18, 2010 10:47:55 PM
May, 2010
May, 2010
Helper functions. These functions, available on DateTime, allow us to format strings. For rapid application development, these are ideal because they are easy to remember and guess.
Note: The methods with the word Long in them produce considerably more verbose output.
VB.NET program that uses DateTime string functions
Module Module1
Sub Main()
' Use string helper functions.
Dim now As DateTime = DateTime.Now
Console.WriteLine(now.ToLongDateString())
Console.WriteLine(now.ToLongTimeString())
Console.WriteLine(now.ToShortDateString())
Console.WriteLine(now.ToShortTimeString())
Console.WriteLine(now.ToString())
End Sub
End Module
Output
Tuesday, May 18, 2010
4:49:57 PM
5/18/2010
4:49 PM
5/18/2010 4:49:57 PM
Short day strings. The .NET Framework gives us the ability to print the representation of a day in short form. The three-letter form returns the day name and truncates it.
Here: In this example, we use a loop construct that iterates through seven days and prints out the short form string for each of them.
For Each, For VB.NET program that prints short day strings
Module Module1
Sub Main()
' Current time.
Dim now As DateTime = DateTime.Now
' Print out all the days.
For index As Integer = 0 To 6
Console.WriteLine(now.ToString("ddd"))
now = now.AddDays(1)
Next
End Sub
End Module
Output
Tue
Wed
Thu
Fri
Sat
Sun
Mon
Long day strings. You can also print out the long day strings using the format string dddd. For more textual output, the longer day string might be preferred.
Here: In this example, we loop over seven consecutive days and print out the long day strings.
VB.NET program that prints long day strings
Module Module1
Sub Main()
Dim now As DateTime = DateTime.Now
For index As Integer = 0 To 6
Console.WriteLine(now.ToString("dddd"))
now = now.AddDays(1)
Next
End Sub
End Module
Output
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
Monday
AM, PM. When you are using a 12-hour based time system, you will typically want to display AM or PM to indicate whether it is morning or evening.
Next: This example prints out AM and PM for two times that are twelve hours apart.
Question: Are you a morning person, or a night person? This program will help you figure this out.
VB.NET program that prints AM and PM
Module Module1
Sub Main()
Dim now As DateTime = DateTime.Now
For index As Integer = 0 To 1
Console.WriteLine(now.ToString("tt "))
now = now.AddHours(12)
Next
End Sub
End Module
Output
PM
AM
Year. The year part of the format string is also important. Typically, you will want a two or four digit year, but a one-digit year is also possible with a single y.
Here: Let's look at some output in an example program that tests yy and yyyy. We see two-digit and four-digit years.
VB.NET program that prints year strings
Module Module1
Sub Main()
' Use the best y patterns.
Dim now As DateTime = DateTime.Now
Console.WriteLine(now.ToString("yy"))
Console.WriteLine(now.ToString("yyyy"))
End Sub
End Module
Output
10
2010
Empty formats. When we use a Nothing, empty, or missing format string, the default ToString implementation is used. It is easiest to just omit the argument when no special format is needed.
VB.NET program that uses empty format strings
Module Module1
Sub Main()
Dim testDate As DateTime = New Date(2019, 1, 1)
Dim nothingString As String = Nothing
' Test the ToString Function.
Console.WriteLine("NOTHING: {0}", testDate.ToString(nothingString))
Console.WriteLine("EMPTY: {0}", testDate.ToString(""))
Console.WriteLine("MISSING: {0}", testDate.ToString())
End Sub
End Module
Output
NOTHING: 1/1/2019 12:00:00 AM
EMPTY: 1/1/2019 12:00:00 AM
MISSING: 1/1/2019 12:00:00 AM
FormatException. Be careful to use a valid format string with DateTime. Some patterns, like the asterisk, will cause a FormatException—lower and uppercase letters should be used instead.
VB.NET program that causes FormatException
Module Module1
Sub Main()
Dim testDate As DateTime = New Date(2000, 1, 1)
Dim result As String = testDate.ToString("*")
End Sub
End Module
Output
Unhandled Exception: System.FormatException: Input string was not in a correct format.
at System.DateTimeFormat.GetRealFormat...
Format characters. You can use a variety of format characters on the DateTime type. For a more complete description, please view the article written for the C# language.
C# FormatNote: The formatting characters used in both languages are identical. The surrounding code syntax is the only difference.
A summary. This article demonstrated the correct use of format strings on the DateTime type. DateTime has many convenience functions, different format character styles and display options.
DateTime 
DateTime requires no custom code on our part. This makes programs easier to maintain and read. The DateTime formatting mechanism can handle most common cases.
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