| Re: Calling data from a structure of pointers? [message #43020] |
Fri, 11 March 2005 09:16 |
Jonathan Greenberg
Messages: 91
Registered: November 2002
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Member |
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Hi all -- looks like I had been doing this is a bit wrong -- it did end up
working right -- *structure.pointer[x] was what I needed (I didn't include
the [] it turns out)...
--j
On 3/10/05 10:57 PM, in article d0rfgv$d6v$1@defalla.upc.es, "Antonio
Santiago" <d6522117@est.fib.upc.es> wrote:
> Jonathan Greenberg wrote:
>
>> How do I retrieve the data the pointers are referring to?
>
> pStr is pointer to a structure variable. This strucutre has 2 pointer
> fields.
>
> pStr = PTR_NEW(
> {
> a: PTR_NEW(10),
> b: PTR_NEW(INDGEN(3))
> })
>
>
> pStr - Pointer variable to structure stored in HEAP memory.
> IDL> help, pStr
> PSTR POINTER = <PtrHeapVar6>
>
> *pStr - The content that pStr points to, that is, the structure
> stored in HEAP memory.l
> IDL> help, *pStr, /STRUCT
> ** Structure <1f06f8>, 2 tags, length=8, data length=8, refs=1:
> A POINTER <PtrHeapVar4>
> B POINTER <PtrHeapVar5>
>
> (*pStr).a - First "get" the strucutre and then access to the firts
> pointer field 'a'.
> IDL> help, (*pStr).a
> <Expression> POINTER = <PtrHeapVar4>
>
> (*(*pStr).a) - The same as above but obtain the content that 'a'
> points (10).
> IDL> help, (*(*pStr).a)
> <PtrHeapVar4> INT = 10
>
> And the same for 'b' field:
> IDL> help, (*pStr).b
> <Expression> POINTER = <PtrHeapVar5>
> IDL> help, (*(*pStr).b)
> <PtrHeapVar5> INT = Array[3]
>
>
> IDL> arr = *(*pStr).b
> IDL> print, arr
> 0 1 2
>
>
>
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| Re: Calling data from a structure of pointers? [message #43028 is a reply to message #43020] |
Thu, 10 March 2005 22:57  |
Antonio Santiago
Messages: 201
Registered: February 2004
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Senior Member |
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Jonathan Greenberg wrote:
> How do I retrieve the data the pointers are referring to?
pStr is pointer to a structure variable. This strucutre has 2 pointer
fields.
pStr = PTR_NEW(
{
a: PTR_NEW(10),
b: PTR_NEW(INDGEN(3))
})
pStr - Pointer variable to structure stored in HEAP memory.
IDL> help, pStr
PSTR POINTER = <PtrHeapVar6>
*pStr - The content that pStr points to, that is, the structure
stored in HEAP memory.l
IDL> help, *pStr, /STRUCT
** Structure <1f06f8>, 2 tags, length=8, data length=8, refs=1:
A POINTER <PtrHeapVar4>
B POINTER <PtrHeapVar5>
(*pStr).a - First "get" the strucutre and then access to the firts
pointer field 'a'.
IDL> help, (*pStr).a
<Expression> POINTER = <PtrHeapVar4>
(*(*pStr).a) - The same as above but obtain the content that 'a'
points (10).
IDL> help, (*(*pStr).a)
<PtrHeapVar4> INT = 10
And the same for 'b' field:
IDL> help, (*pStr).b
<Expression> POINTER = <PtrHeapVar5>
IDL> help, (*(*pStr).b)
<PtrHeapVar5> INT = Array[3]
IDL> arr = *(*pStr).b
IDL> print, arr
0 1 2
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| Re: Calling data from a structure of pointers? [message #43030 is a reply to message #43028] |
Thu, 10 March 2005 15:09 |
R.G.Stockwell
Messages: 163
Registered: October 2004
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Senior Member |
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"Jonathan Greenberg" <usenet@estarcion.net> wrote in message
news:BE560C66.3FE3%usenet@estarcion.net...
> Hopefully this'll be a quicky -- I have a structure of pointers, so if I,
> for instance, print,structure.pointername I get something like:
>
> <PtrHeapVar5917><PtrHeapVar5922>
This is an odd result.
My guess is that structure.pointername is a structure of pointers.
(i.e. you have a stucture where the tag "pointername" is a structure
that has two pointers in it.
Anyways, here is a snippet showing how the structures and pointers work:
s = {p1:ptr_new(/alloc),p2:ptr_new(/alloc)}
pointtostruct = ptr_new(/alloc)
*pointtostruct = s
*s.p1 = 15
*s.p2 = 'hello'
print,'s.p1'
print,s.p1
print,'s.p2'
print,s.p2
print,'*s.p1'
print,*s.p1
print,'pointtostruct'
print,pointtostruct
print,'*pointtostruct'
print,*pointtostruct
print,'*(*pointtostruct).p1'
print,*(*pointtostruct).p1
end
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| Re: Calling data from a structure of pointers? [message #43031 is a reply to message #43030] |
Thu, 10 March 2005 14:46 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Jonathan Greenberg writes:
> Hopefully this'll be a quicky -- I have a structure of pointers, so if I,
> for instance, print,structure.pointername I get something like:
>
> <PtrHeapVar5917><PtrHeapVar5922>
>
> I want to ACCESS the data from that structure tho, but:
>
> print,*structure.pointername doesn't work, nor does
> print,structure.*pointername nor:
>
> tempvar=structure.pointername
> print,*tempvar
>
> How do I retrieve the data the pointers are referring to?
If you really have a structure of pointers, then this *must*
work:
IDL> Print, *structure.pointername
Because structure dereferences have a higher order of precidence
than pointer dereferences.
But from your description, it seems more likely that structure
is a pointer to a structure of pointers. (I can't really tell
*what* you have there.)
Perhaps something like this would work with whatever it
is you have:
*(*structure).pointername
You might find this article helpful:
http://www.dfanning.com/misc_tips/precedence.html
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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