| Re: Tough System Variable Question for the IDL Gurus [message #68621] |
Wed, 11 November 2009 17:51 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
> Maybe a pointer *will* work.
>
> IDL> defsysv, '!tester', Ptr_New(5)
> IDL> help, !tester
> <Expression> POINTER = <PtrHeapVar795>
> IDL> help, *!tester
> <PtrHeapVar795> LONG = 5
> IDL> ptr_Free, !tester
> IDL> !tester = Ptr_New(/ALLOCATE_HEAP)
> IDL> help, /heap
> Heap Variables:
> # Pointer: 1
> # Object : 0
>
> <PtrHeapVar2> UNDEFINED = <Undefined>
Well, this could be confusing. Let me take my example
all from the same IDL session:
IDL> defsysv, '!tester', Ptr_New(5)
IDL> help, !tester
<Expression> POINTER = <PtrHeapVar1>
IDL> help, *!tester
<PtrHeapVar1> LONG = 5
IDL> Ptr_Free, !tester
IDL> !tester = Ptr_New(/Allocate_Heap)
IDL> help, !tester
<Expression> POINTER = <PtrHeapVar2>
IDL> help, *!tester
<PtrHeapVar2> UNDEFINED = <Undefined>
IDL> help, /heap
Heap Variables:
# Pointer: 1
# Object : 0
<PtrHeapVar2> UNDEFINED = <Undefined>
IDL> Ptr_Free, !tester
IDL> help, /heap
Heap Variables:
# Pointer: 0
# Object : 0
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Tough System Variable Question for the IDL Gurus [message #68622 is a reply to message #68621] |
Wed, 11 November 2009 17:45  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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ben.bighair writes:
> Why do you want to remove a system variable?
I don't know. I don't always come up with the questions.
> Would making the system variable a pointer or object work? At least
> then you could destroy/dereference them. I recall that I used an
> object as a system variable for the old "CoolHelp" thingy. And
> another thing, you *are* an IDL guru.
Yeah, but a guru who didn't know the answer. :-)
Maybe a pointer *will* work.
IDL> defsysv, '!tester', Ptr_New(5)
IDL> help, !tester
<Expression> POINTER = <PtrHeapVar795>
IDL> help, *!tester
<PtrHeapVar795> LONG = 5
IDL> ptr_Free, !tester
IDL> !tester = Ptr_New(/ALLOCATE_HEAP)
IDL> help, /heap
Heap Variables:
# Pointer: 1
# Object : 0
<PtrHeapVar2> UNDEFINED = <Undefined>
Thanks for the tip and the fish story, Ben! :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Tough System Variable Question for the IDL Gurus [message #68625 is a reply to message #68622] |
Wed, 11 November 2009 16:12 |
ben.bighair
Messages: 221
Registered: April 2007
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Senior Member |
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On Nov 11, 5:26 pm, FÖLDY Lajos <fo...@rmki.kfki.hu> wrote:
> On Wed, 11 Nov 2009, David Fanning wrote:
>> OK, you IDL gurus. How do you delete an IDL system variable
>> you have created with DefSysV without getting out of the IDL session?
>
>> IDL> DefSysV, '!TESTER', 5
>> IDL> DelVar, !TESTER
>> % DELVAR: Expression must be named variable in this context: <INT
>> ( 5)>.
>
>> IDL> Undefine, !Tester
>> IDL> Help, !Tester
>> <Expression> INT = 5
>
>> My current thinking is that it is not possible. Any good ideas?
>
>> Cheers,
>
>> David
>
> You are right, it is not possible:
>
> "System variables have a predefined type and structure that cannot be
> changed." (IDL Reference Guide)
>
> regards,
> Lajos
Hi,
Why do you want to remove a system variable?
Would making the system variable a pointer or object work? At least
then you could destroy/dereference them. I recall that I used an
object as a system variable for the old "CoolHelp" thingy. And
another thing, you *are* an IDL guru.
Cheers,
Ben
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| Re: Tough System Variable Question for the IDL Gurus [message #68630 is a reply to message #68625] |
Wed, 11 November 2009 14:26 |
Foldy Lajos
Messages: 268
Registered: October 2001
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Senior Member |
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On Wed, 11 Nov 2009, David Fanning wrote:
> OK, you IDL gurus. How do you delete an IDL system variable
> you have created with DefSysV without getting out of the IDL session?
>
> IDL> DefSysV, '!TESTER', 5
> IDL> DelVar, !TESTER
> % DELVAR: Expression must be named variable in this context: <INT
> ( 5)>.
>
> IDL> Undefine, !Tester
> IDL> Help, !Tester
> <Expression> INT = 5
>
> My current thinking is that it is not possible. Any good ideas?
>
> Cheers,
>
> David
>
You are right, it is not possible:
"System variables have a predefined type and structure that cannot be
changed." (IDL Reference Guide)
regards,
Lajos
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