RE: data structure overlay question.

[Jim Langston <jlangston@xxxxxxxxxxx>]

From: Richard B Baird [mailto:rbaird@esourceconsulting.com]

<SNIP>

>DDSINPUT        E DS                  EXTNAME(DSUPDPAG) INZ

>D @QzAmt          S               *   INZ(%addr(qzamt1))
>D @QzChk          S               *   INZ(%addr(qzchk1))

>D $QzAmt          S                   like(QZAMT1 ) based(@qzamt)
>D                                      dim(12)
>D $QzChk          S                   like(QZCHK1 ) based(@qzchk)
>D                                      dim(12)

1. the '*' in the field length implies "variable length"?

The * in the field type (not length) implies a pointer.

2. is it the "based" keyword on the $qzxxx that eventually defines the
length of the @qzxxx fields?

The based keyword defines this as a variable(array) that will start at
the memory pointed to by @qzamt.

3. or is it the fact that the next field in the DS (@qzchk) starts at the
address of QZCHK1 that defines the length of @qzamt?   if so, what defines
the length of @qzchk?

The length if @qzchk is a pointer length.  It is a pointer and you can't
use it's memory directly, you need another variable based on it to look
at what it points to.

A little confusing, I know.  We want the array @qzamt to start at the
same spot in memory as qzamt1.  To do this, we first set up a pointer
to point to the same memory location (which is what INZ(%addr(qzamt1))
is doing.  Then we set our array to be based on this pointer (which is
what based(@qzamt) is doing.

All you really need to remember is, create a pointer pointing to the
memory you want to use, then set up your variable/array/structure and
base it on that pointer.

HTH,

Jim Langston