Handling Dates and Times in VB.net
By: Steven Holzner in VB.net Tutorials on 2008-11-25
One of the biggest headaches a programmer can have is working with dates. Handling hours, minutes, and seconds can be as bad as working with shillings, pence, and pounds. Fortunately, Visual Basic has a number of date and time handling functions, which appear in Table below-you can even add or subtract dates using those functions. VB6 programmers will notice a number of new properties in this table.
|
To do this |
Use this |
|---|---|
|
Get the current date or time |
Today, Now, TimeofDay, DateString, TimeString |
|
Perform date calculations |
DateAdd, DateDiff, DatePart |
|
Return a date |
DateSerial, DateValue |
|
Return a time |
TimeSerial, TimeValue |
|
Set the date or time |
Today, TimeofDay |
|
Time a process |
Timer |
Here's an example in which I'm adding 22 months to 12/31/2001 using DateAdd-you might note in particular that you can assign dates of the format 12/31/2001 to variables of the Date type if you enclose them inside # symbols:
Imports System.Math
Module Module1
Sub Main()
Dim FirstDate As Date
FirstDate = #12/31/2001#
System.Console.WriteLine("New date: " & DateAdd_
(DateInterval.Month, 22, FirstDate))
End Sub
End Module
Here's what you see when you run this code:
New date: 10/31/2003 Press any key to continue
There's something else you should know-the Format function makes it easy to format dates into strings, including times. For easy reference, see Table 2.11, which shows some ways to display the date and time in a string-note how many ways there are to do this.
|
Format Expression |
Yields this |
|---|---|
|
Format(Now, "M-d-yy") |
"1-1-03" |
|
Format(Now, "M/d/yy") |
"1/1/03" |
|
Format(Now, "MM - dd - yy") |
"01 /01 / 03" |
|
Format(Now, "ddd, MMMM d, yyy") |
"Friday, January 1, 2003" |
|
Format(Now, "d MMM, yyy") |
"1 Jan, 2003" |
|
Format(Now, "hh:mm:ss MM/dd/yy") |
"01:00:00 01/01/03" |
|
Format(Now, "hh:mm:ss tt MM-dd-yy") |
"01:00:00 AM 01-01-03" |
You can also compare dates and times directly. For example, here's how you loop until the current time (returned as a string by TimeString) exceeds a certain time; when the time is up, the code beeps using the Visual Basic Beep function:
While TimeString < "15:45:00" End While Beep()
| Tip |
Don't use the above code snippet for more than an example of how to compare times! The eternal looping while waiting for something to happen is a bad idea in Windows, because your program monopolizes a lot of resources that way. Instead, set up a Visual Basic Timer and have a procedure called, say, every second. |
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