hi guys,
plz tell me why global data area(GDA) is accessed only for programme and external subroutine.
not for subprogramme ,internal subroutine and helproutine…
There are two philosopies:
- Share data in a GDA and FETCH RETURN
- Share data via Parameter and CALLNAT
So from my point of view the completely separated memory for CALLNAT makes sense.
BTW: If you want to use GDA-like variables in a subprogram use DEFINE DATA INDEPENDENT.
GDA is accessable for an interal subroutine.
A Natural subprogram, in a very real sense, is a “generic” subroutine. The original design philosophy behind “subroutines”, many many years ago, was that they should be independent of the calling programs.
That is, you passed the required arguments to a subroutine, it did its thing, and it passed back the required output.
As a programmer “using a subroutine”, I was free to change anything in my calling program so long as the arguments I passed to the subroutine conformed to expected format and length. Similarly, as a programmer of a subroutine, as long as I did not change the interface, I could do anything I wanted within the subroutine.
Now suppose a Natural program and subprogram “shared” a Global Data Area. All of a sudden, the two routines are no longer independent of one another. If there is a variable in the GDA called #SUM which is used by both a program and a subprogram, and the programmer of the subprogram wants to change the name to something more descriptive like #SUM-OF-MONTHLY-EXPENSES. In order to do that, assuming they had the proper authority, they would change the GDA.
BUT, now everyone who used #SUM from the GDA, whether they called the subprogram or not, would have to change their code. What a nightmare.
That is almost assuredly one reason why subprograms are maintained as an independent entity.
steve