| HomeSearch | VB.NET DateTime FormatUse 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 DateTimeas 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 requiresno 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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