Re: RPG IV Pointers

[Jim Langston <jlangston@xxxxxxxxxxxxxxxx>]

I don't know why I am not getting this.  I just don't understand.

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

In this case, if I access the data pointed to by MyPointer, it is the same
data that is stored in MyField, correct?

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

Where, in this example, is MyField?  Isn't' it the same case, since MyField
is based on MyPointer?

Perhaps I am not understanding what the BASED keyword is doing.
Just what does it do?

Regards,

Jim Langston

bmorris@ca.ibm.com wrote:

> 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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