Difference of two dates in ILE RPG
To calculate difference between two dates, we use the built in function %Diff. This function can be used to get the difference in days, months or years as per our wish/requirement. One word of caution though; the remainder value is not returned as decimal parts.

So to calculate exact difference, this function should be used to get the difference in days and this difference should be divided by appropriate no like 365 or 365.25 to get exact difference year in decimal. A similar approach should be followed for months. Otherwise separate years, months and days difference should be calculated and should be clubbed together by some logic to suit our specific business requirement.

In this article we will learn to find the difference between two date fields in years, months and days respectively.

Just like any other date mathematics, here also, the first step is to get the two numeric dates into date data types. Once we have two valid dates of date data type we just have to get the difference using the %Diff built in functions.

The syntax of function %Diff is as below

%Diff(Date1: Date2: *Years/*Months/*Days)

Here Date1 and Date2 are two actual dates. And *Years, *Months and *Days are the difference of which are returned. i.e. *Years will return the difference of years.

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Which date is in past?
Ideally date1 should be a future date as compared to Date2. However, if Date1 is a future date as compared to Date2 the return values would be negative numeric values. So, this is a good way to find which date occurred earlier in a pair of dates.

The following example would make the ILE RPG date difference concept clearer.

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Example to get difference of two dates in RPG IV:-

DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++
D W@YMD1          S              6  0 Inz(011219)                      
D W@YMD2          S              6  0 Inz(000101)                      
D W@Date1         S               D                                    
D W@Date2         S               D                                    
D w@Yrs           S              2  0 Inz                              
D w@Mons          S              3  0 Inz                              
D w@Days          S              5  0 Inz                              
 *. 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7 ...+.
 * First step is to get actual dates                                   
C     *YMD          Move      W@YMD1        W@Date1                    
C     *YMD          Move      W@YMD2        W@Date2                    
 * Get difference of years                                              
C                   Eval      W@Yrs = %Diff(W@Date1: W@Date2: *Years)  
 * Get difference of months                                             
C                   Eval      W@Mons = %Diff(W@Date1: W@Date2: *Months)
* Get difference of days                                               
C                   Eval      W@Days = %Diff(W@Date1: W@Date2: *Days)  
C     W@Yrs         Dsply                                              
C     W@Mons        Dsply                                              
C     W@Days        Dsply                                              
C                   Return                                            

Output:-

DSPLY   1   
DSPLY   23  
DSPLY    718

As usual comments and feedbacks are most welcome.