Re: RPG IV Pointers

[bmorris@xxxxxxxxxx]

>Date: Mon, 28 Feb 2000 14:51:50 -0800
>From: Jim Langston <jlangston@conexfreight.com>
>
>D MyPointer           S            *
>D MyField             S          50
>C                  Eval     MyPointer = %Addr(MyField)
>
>Is that equivalent to:
>
>D MyPointer           S            *
>D MyField             S          50   Based(MyPointer)
> ...

Jim, no, they're not equivalent.

In the first example, MyField occupies a fixed storage
location.  MyPointer is not specifically connected to
MyField.

In the second example, MyField occupies a variable storage
location (the storage pointed to by MyPointer).  MyPointer
is explicitly associated with MyField; you can access the
storage that MyPointer points to by using the name MyField.

Your examples ARE somewhat similar: in both,MyPointer and
MyField associated with the same storage, **sometimes**.
The difference is that in the first example, this depends on
MyPointer being set to the address of MyField; in the
second example, it depends on MyPointer being non-null.

For those who speak C, here are rough equivalents to the
RPG examples above.

Example 1: int *MyPointer;
           int MyField;
           MyPointer = &MyField;

Example 2: int *MyPointer; // MyField is equiv. to *MyPointer

Barbara Morris


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