Re: Defining datastructure with ExtName/LikeRec

Rory Hewitt wrote:

So are EXTNAME and LIKEREC basically implemented in the same way under the
covers?

Sort of. At least, they end up with the same result, having a data structure whose subfields match the fields in a file.

Scott pointed out that doing an explicit read into a LIKEREC DS simply moved
the record buffer, whereas doing an implicit read into an EXTNAME DS did a
field-by-field move, but is that the only difference (under the covers)?

The difference between moving the entire buffer vs field-by-field depends on how you code the READ, not on how you defined the data structure.

If you code a data structure in the result field of the READ, it moves the record buffer. If you don't code a data structure in the result field, it uses the I specs. If the I specs match the subfields of a data structure, the field-by-field move populates the data structure.

To do an implicit read into a LIKEREC, you need PREFIX('DSNAME.') on the F spec, same as you would if you coded QUALIFIED with an EXTNAME. This makes the fields associated with the file have the same names as the subfields of the LIKEREC ds.

Compile a program like this with dbgview(*list) and run it in the debugger. When you step on the READ, you'll see it reading into subfields MYDS.FLD1, MYDS.FLD2 etc.

H option(*debugio)
Fmyfile IF E DISK PREFIX('MYDS.')
D myds DS LIKEREC(myrec)
read myrec;