| IDL V5 and Pointers [message #9620] |
Wed, 23 July 1997 00:00  |
martin
Messages: 18
Registered: January 1993
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Junior Member |
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I just started using pointers in IDL. Does anyone know how to get create a
pointer that points to an existing variable, without duplicating the
variable and without making it undefined?
For example:
x=findgen(1000,1000,1000) ; a big array
.
.
.
lots of code
.
.
.
.
ptr=ptr_new()
ptr=&x ; this syntax is derived from C and is not valid in IDL.
; Does anyone know how to do the equivalent in IDL?
Thanks,
Charles Martin
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| Re: IDL V5 and Pointers [message #9678 is a reply to message #9620] |
Fri, 25 July 1997 00:00  |
David Foster
Messages: 341
Registered: January 1996
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Senior Member |
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Charles Martin wrote:
>
> I just started using pointers in IDL. Does anyone know how to get create a
> pointer that points to an existing variable, without duplicating the
> variable and without making it undefined?
>
> For example:
>
> x=findgen(1000,1000,1000) ; a big array
> .
> .
> .
> lots of code
> .
> .
> .
> .
> ptr=ptr_new()
> ptr=&x ; this syntax is derived from C and is not valid in IDL.
> ; Does anyone know how to do the equivalent in IDL?
Charles -
This facility does not exist in IDL, and I believe it is because
of the rather unstable nature of variables and their addresses in
IDL. Hopefully someone will explain this more completely, as I
would like to hear it myself.
You can always create your pointer like this:
ptr = ptr_new(x) ; Your big array, x is STILL defined!
Creating your pointer does not undefine x. If you don't want two
copies you can do:
ptr = ptr_new( findgen(1000,1000,1000) )
Dave
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
David S. Foster Univ. of California, San Diego
Programmer/Analyst Brain Image Analysis Laboratory
foster@bial1.ucsd.edu Department of Psychiatry
(619) 622-5892 8950 Via La Jolla Drive, Suite 2200
La Jolla, CA 92037
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
"I have this theory that if we're told we're bad,
then that's the only idea we'll ever have.
But maybe if we are surrounded in beauty,
someday we will become what we see." - Jewel Kilcher
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