Articolo
11/18/2011

DateAndTime.DateAdd Method (DateInterval, Double, DateTime)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Returns a Date value containing a date and time value to which a specified time interval has been added.

Namespace: Microsoft.VisualBasic
Assembly: Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)

Syntax

'Declaration
Public Shared Function DateAdd ( _
    Interval As DateInterval, _
    Number As Double, _
    DateValue As DateTime _
) As DateTime

public static DateTime DateAdd(
    DateInterval Interval,
    double Number,
    DateTime DateValue
)

Parameters

Interval
Type: Microsoft.VisualBasic.DateInterval
Required. DateInterval enumeration value or String expression representing the time interval you want to add.

Number
Type: System.Double
Required. Double. Floating-point expression representing the number of intervals you want to add. Number can be positive (to get date/time values in the future) or negative (to get date/time values in the past). It can contain a fractional part when Interval specifies hours, minutes, or seconds. For other values of Interval, any fractional part of Number is ignored.

DateValue
Type: System.DateTime
Required. Date. An expression representing the date and time to which the interval is to be added. DateValue itself is not changed in the calling program.

Return Value

Type: System.DateTime
Returns a Date value containing a date and time value to which a specified time interval has been added.

Remarks

You can use the DateAdd function to add or subtract a specified time interval from a date. For example, you can calculate a date 30 days from today or a time 45 minutes before now.

To add days to DateValue, you can use DateInterval.Day, DateInterval.DayOfYear, or DateInterval.Weekday. These are treated as equivalent because DayOfYear and Weekday are not meaningful time intervals.

The DateAdd function never returns an invalid date. If necessary, the day part of the resulting date is adjusted downward to the last day of the resulting month in the resulting year. The following example adds one month to January 31:

Dim NextMonth As Date = DateAdd(DateInterval.Month, 1, #1/31/1995#)

In this example, DateAdd returns #2/28/1995#, not #2/31/1995#. If DateValue is #1/31/1996#, it returns #2/29/1996# because 1996 is a leap year.

Note:
DateAdd uses the current calendar setting from the CurrentCulture property of the CultureInfo class in the System.Globalization namespace. The default CurrentCulture values are determined by Control Panel settings.

Since every Date value is supported by a DateTime structure, its methods give you additional options in adding time intervals. For example, you can add a fractional number of days, rounded to the nearest millisecond, to a Date variable as follows:

Dim NextTime As Date = Now        ' Current date and time.
NextTime = NextTime.AddDays(3.4)  ' Increment by 3 2/5 days.

The Interval argument can have one of the following settings.

Enumeration value	String	Unit of time interval to add
DateInterval.Day	d	Day; truncated to integral value
DateInterval.DayOfYear	y	Day; truncated to integral value
DateInterval.Hour	h	Hour; rounded to nearest millisecond
DateInterval.Minute	n	Minute; rounded to nearest millisecond
DateInterval.Month	m	Month; truncated to integral value
DateInterval.Quarter	q	Quarter; truncated to integral value
DateInterval.Second	s	Second; rounded to nearest millisecond
DateInterval.Weekday	w	Day; truncated to integral value
DateInterval.WeekOfYear	ww	Week; truncated to integral value
DateInterval.Year	yyyy	Year; truncated to integral value

Examples

This example takes a date and, using the DateAdd function, displays a corresponding date a specified number of months in the future.

Dim StartDate = DateString
Dim Months As Double
Dim SecondDate As Date
Dim IntervalType As DateInterval
IntervalType = DateInterval.Month   ' Specifies months as interval.
Months = 6
SecondDate = CDate(StartDate)
Dim Msg = "New date: " & DateAdd(IntervalType, Months, SecondDate)

Version Information

Silverlight

Supported in: 5, 4, 3

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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