Re: DS fields

[dhandy@xxxxxxxxxxx (Douglas Handy)]

Mark,

> Then why can you have an input field coming from files?

When a record format is read (DB, dspf, etc), the entire record
contents are passed to a "buffer" area.  RPG then performs implicit
moves from the buffer to the separate memory area used as working
storage for each field referenced by the program.  (With DEBUG(*YES),
all fields in the record format have working storage fields assigned
and moved.  Without DEBUG(*YES), only referenced fields are allocated
field areas outside the buffer.)  The opposite happens on an output
operation -- the fields are implicity moved to the buffer area first.

If the field name does not appear in a DS, then the field's storage
area is just like any other stand-alone variable.  It will not overlap
with any other fields.  But unlike a stand-alone field, it has
implicit moves to/from the record format buffer after a read and
before a write.

The only difference with a rec fmt's field name appearing in a DS is
that you have more direct control over the memory space which includes
the working storage copy of the field.  By putting it in a DS you can
perform tricks by subsetting, overlaying, redefining, etc the memory
space including the field contents.

It stands to follow that a field name therefore cannot be part of more
than one data structure because it must resolve to a single memory
address.

If this is still not clear, ask again.

Doug
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