Re[2]: Prototyping printf()

[bmorris@xxxxxxxxxx]

>Date: Thu, 28 Sep 2000 19:41:40 -0700
>From: "Eric N. Wilson" <doulos1@home.com>
>
>> Not very close either.  A pointer could be turned into a string, but the
>> AS/400 isn't going to let you turn a string back into a valid pointer;
so it
>> wouldn't be able to be used.
>
>Ah I beg to differ with you. Try this, declare a data structure and
>make it have one sub field of a pointer data type. Then make a second
>data structure just like the first. Then assign the address of the
>pointer in the first data structure to your favorite variable. Then
>eval DS2 = DS1 and low and behold the pointer in DS2 is valid :-)

Eric, what you are doing is copying one data structure containing a
pointer to another data structure containing a pointer.  This is not
the same as turning a string containing the hex value of a pointer
back into a pointer.  An AS/400 pointer is more than just the 16 bytes
holding its hex value - its "pointerness" is also dependent on a bit
being set "somewhere else".

Try this:

D charfld         S             16a
D ds              DS
D   pointer                       *

C          eval       pointer = %addr(x)
C          eval       charfld = ds
C          eval       ds = charfld

Now test "pointer".  It won't be valid.

(Actually, there is no guarantee that this will fail, but there
is also no guarantee that it will work.  It may depend on the
alignment of charfld, and on the way RPG chooses to copy the
data on the evals.)

Barbara Morris


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