DateDiff

Gets the difference of two dates measured by a specified interval

Syntax
	KeyPgDeclareDeclare KeyPgFunctionFunction DateDiff ( KeyPgByrefByRef interval KeyPgAsAs KeyPgConstQualifierConst KeyPgStringString, KeyPgByvalByVal 
	serial1 KeyPgAsAs KeyPgDoubleDouble, KeyPgByvalByVal serial2 KeyPgAsAs KeyPgDoubleDouble, KeyPgByvalByVal firstdayofweek KeyPgAsAs KeyPgLongLong 
	= fbUseSystem, KeyPgByvalByVal firstdayofyear KeyPgAsAs KeyPgLongLong = fbUseSystem ) KeyPgAsAs KeyPgLongintLongInt

Usage
	#include "vbcompat.bi"
	result = DateDiff( interval, date_serial1, date_serial2 [, 
	firstdayofWeek [, firstweekofyear ] ] )

Parameters
	interval
		the unit of time (interval) with which to measure the difference
	date_serial1
		starting date serial
	date_serial2
		end date serial
	firstdayofweek
		first day of the week
	firstdayofyear
		first day of the year

Return Value
	Returns a KeyPgLongintLongInt corresponding to the number of intervals found between 
	two ProPgDatesDate Serials.

	If date_serial1 > date_serial2, the result is negative.

Description
	interval is specified as follows:

			Ŀ
			valueinterval             
			yyyy years                
			q    quarter(three months)
			m    months               
			w     seven day periods   
			 ww  calendar weeks       
			d,y  days                 
			h    hours                
			n    minutes              
			s    seconds              
			
  

	first_dayofweek Affects the counting when 'ww' interval is used.

			Ŀ
			value  first day of weekconstant   
			omittedsunday                      
			0      local settings   fbUseSystem
			1      sunday           fbSunday   
			2      monday           fbMonday   
			3      tuesday          fbTuesday  
			4      wednesday        fbWednesday
			5      thursday         fbThursday 
			6      friday           fbFriday   
			7      saturday         fbSaturday 
			

	first_weekofyear specifies which year (previous or next) that the week 
	which spans the end of one year and the beginning of the next should 
	included with.

			Ŀ
			valuefirst week of year                   constant       
			0    local settings                       fbUseSystem    
			1    January 1's week                     fbFirstJan1    
			2    first weeks having 4 days in the yearfbFirstFourDays
			3    first full week of year              fbFirstFullWeek
			

	Notice if you do an arithmetical subtraction of two date serials you get 
	the difference in days.

	The compiler will not recognize this function unless vbcompat.bi or 
	datetime.bi is included.

Example
	#include "vbcompat.bi"

	Dim s As String, d1 As Double, d2 As Double

	Line Input "Enter your birthday: ", s

	If IsDate( s ) Then
	  d1 = DateValue( s )
	  d2 = Now()

	  Print "You are " & DateDiff( "yyyy", d1, d2 ) & " years old."
	  Print "You are " & DateDiff( "d", d1, d2 ) & " days old."
	  Print "You are " & DateDiff( "s", d1, d2 ) & " seconds old."

	Else
	  Print "Invalid date"

	End If

Differences from QB
	* Did not exist in QB. This function appeared in Visual Basic.

See also
	* ProPgDatesDate Serials

