Converting a date in COBOL

Question

So im reading a mmddyyyy (01012000) date into a pic x (8) and im wondering how I can create a new variable with the previous variables info into yyyymmdd (20000101) format. Im sure there must be some way to do this with substrings or what not?

Answer 1

@ScottNelson has provided the "using substrings" part of the answer, following is the "or what not" part of the answer.

01  mmddyyyy.
    05  mm     pic xx.
    05  dd     pic xx.
    05  yyyy   pic xxxx.

01  yyyymmdd.
    05  yyyy   pic xxxx.
    05  mm     pic xx.
    05  dd     pic xx.

move corresponding mmddyyyy to yyyymmdd

Answer 2

In working storage:

77  mmddyyyy-date pic x(8).
77  yyyymmdd-date pic x(8).

In your procedure division logic:

move mmddyyyy-date(1:2) to yyyymmdd-date(5:2)
move mmddyyyy-date(3:2) to yyyymmdd-date(7:2)
move mmddyyyy-date(5:4) to yyyymmdd-date(1:4)

Answer 3

   01  a-name-to-describe-the-source-date.
       05  antdtsd-dd                      PIC XX.
       05  antdtsd-mm                      PIC XX.
       05  antdtsd-yyyy                    PIC XXXX.

   01  a-name-to-describe-the-destination-date.
       05  antdtdd-yyyy                    PIC XXXX.
       05  antdtdd-mm                      PIC XX.
       05  antdtdd-dd                      PIC XX.

Or

   01  a-name-to-describe-the-source-date  PIC X(8).
   01  FILLER 
       REDEFINES a-name-to-describe-the-source-date.
       05  antdtsd-dd                      PIC XX.
       05  antdtsd-mm                      PIC XX.
       05  antdtsd-yyyy                    PIC XX.

   01  a-name-to-describe-the-destination-date.
   01  FILLER 
       REDEFINES a-name-to-describe-the-destination-date.
       05  antdtdd-yyyy                    PIC XX.
       05  antdtdd-mm                      PIC XX.
       05  antdtdd-dd                      PIC XX.

Then

       MOVE antdtsd-dd                     TO antdtdd-dd
       MOVE antdtsd-mm                     TO antdtdd-mm
       MOVE antdtsd-yyyy                   TO antdtdd-yyyy

Firstly, you are overstating things if you call this "conversion". It is a simple rearrangement of data.

Secondly, there are many ways to do this. Which way do you do it? COBOL tends to be coded by "teams", and if you do this for a job, you will be best served by doing it how others on your team do it.

You've been shown two ways: reference-modification and using CORRESPONDING (which, if you see it in real code, will often be abbreviated to CORR - who's going to type CORRESPONDING if the intent is not to type much...?).

How otherwise to chose between them? Performance? They'll likely generate identical code. So the compiler is out of it. Understandability to the human reader? For me, that is very important in COBOL (or any language).

Two problems with the reference-modification. Typo? No problem, code will compile and execute. And you'll find it in testing. Won't you? At some point? And wasting all the time expended until you find it. The second is, what does (5:4) mean? When someone tells you "that program is doing something odd with years", you have to first find that the year is disguised as (5:4). Oh, and (1:4). Great, you've not even started looking for the issue with the program yet, and you still have to check the positions and lengths are correct. OK, a date is a trivial example, but reference-modification-users presumably apply it to everything they can (if not, why apply it to a date)? So, have fun reading.

Oh, and COBOL doesn't have "strings", it has fixed-length fields. Reference-modification creates fields

The CORR. Using this saves lots of typing (the it's reason it exists is probably due to punched-cards, and the way many COBOL programs would process input data and create new output data. Programs on punched-cards, so a genuine reason to reduce typing - for punched-card programs).

Well, tis modern times now.

Let's say you want to use the "month" as a subscript to get the month-name if the year is 2005.

IF yy OF yyyymmdd EQUAL TO "2005"
    MOVE month-name-in-table ( mm OF yyyymmdd ) TO ...
END_IF

(that assumes mm OF yyyymmdd is defined as numeric).

Do you want to scatter "qualification" (the use of OF or IN to make a name unique by referring to something it belongs to) throughout a program, just so you can use CORR?