DateAddDay

See Also: Time and Date Functions

Purpose

The DateAddDay function adds or subtracts a given number of days to a given DateTime variable dtVar.

 

If the added unit exceeds the range of a DateTime section, the entire DateTime is adjusted. For example, adding 48 to hours would add 2 days to the DateTime variable.  The returned DateTime variable is always valid.

The DateTime variable passed to the function must be valid and non-null. If this is not the case a DFERR_INVALID_DATETIME error will be raised. You can use the IsDateValid and IsNullDateTime functions to make sure the value you are passing to this function is valid.

This differs from the DateSetXxx functions which do not perform date arithmetic (i.e., they just set the one DateTime section) and neither the incoming or outgoing DateTime variable is tested for validity.

This is part a family of DateTime manipulation functions which includes DateAddDay, DateAddHour, DateAddMillisecond, DateAddMinute, DateAddMonth, DateAddSecond, DateAddYear. The DateSet and CurrentDateTime functions can be used to initialize a DateTime value.

Return Type

DateTime

Syntax

DateAddDay( {dtVar}, {iDaysToAdd} )

Where:

Example

This example sets the date of a DateTime variable and then adds 1 day to the time.

Procedure Test

    DateTime dtVar

 

    Move (DateSet(2015, 9, 26)) to dtVar

    Move (DateAddDay(dtVar,1)) to dtVar

 

    // This will print (using US date settings):

    // 9/27/2015 12:00:00 AM

    Showln dtVar

End_Procedure

Example

This example sets the date of a DateTime variable and then subtracts 1 day from the time.

Procedure Test

    DateTime dtVar

 

    Move (DateSet(2015, 9, 26)) to dtVar

    Move (DateAddDay(dtVar,-1)) to dtVar

 

    // This will print (using US date settings):

    // 9/25/2015 12:00:00 AM

    Showln dtVar

End_Procedure

 

DateAddXxx Functions vs. DateSetXxx

The DateAddXxx functions differs from the DateSetXxx functions which do not perform date arithmetic (i.e., they just set the one DateTime section) and neither the incoming or outgoing DateTime variable is tested for validity.  

In most cases, the DateSet function and the DateAddXxx (DateAddDay, DateAddHour, DateAddMillisecond, DateAddMinute, DateAddMonth, DateAddSecond, DateAddYear) functions can be used in preference to the DateSetXxx (DateSetDay, DateSetHour, DateSetMillisecond, DateSetMinute, DateSetMonth, DateSetSecond, DateSetYear) functions. The DateSetXxx functions are lower level and should be rarely used.