Jeff,
So, provided my prototype and the PI of the called procedure match, if I
specifiy CONST, the compiler will *never* allow the value to be changed in
the called procedure?
When using a subprocedure (as opposed to external program call via a
prototype), then the compile will ensure that variable name is not updated.
But as Alan points out, you can circumvent that by updating the same memory
location due to DS overlay or whatever.
Also note that with CONST, the original value may or may not be passed by
reference. When the original field is the same type/length/etc as the CONST
parm, the field is passed by reference. In this case an obfuscated change
(like a DS) will alter the original field. However, with CONST if the field
types are not the same, the a temporary copy will be made and it is passed
by value. In this case, even an obfuscated change will not alter the
original field because only the copy is updated.
Or at least that is my understanding of CONST.
Note that a service program is the same as an internal subprocedure in this
regard. It is a prototyped call to an external program (not *SRVPGM) which
I believe will not enforce the CONST checking.
So while a VALUE will always pass by value (thus safeguarding the original
from any potential for change), a CONST may or may not be passed by value
depending on whether the passed field already has the right attributes.
Doug
midrange.com
