| Re: Is a dynamically sized pointer array object component possible? [message #66548 is a reply to message #66531] |
Thu, 21 May 2009 15:21   |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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Paul van Delst wrote:
> Hello,
>
> I'm trying to create an object with a component that is a pointer
> array... but I don't know the size of the array ahead of time. In
> structure-speak, I'm doing this:
>
> IDL> x={blah,y:ptr_new()}
> IDL> x.y=ptr_new(ptrarr(4))
> IDL> (*x.y)[0] = ptr_new(dindgen(20))
> IDL> help, *(*x.y)[0]
> <PtrHeapVar1> DOUBLE = Array[20]
>
> Now, if I knew what size of array I needed in advance (in this example,
> 4), I could do the following:
>
> IDL> x={blah,y:ptrarr(4)}
> IDL> x.y[0] = ptr_new(dindgen(20))
> IDL> help, *x.y[0]
> <PtrHeapVar1> DOUBLE = Array[20]
>
> The latter example is preferable since
> a) it more closely reflect the data, and
> b) the dereferencing is clearer.
>
> I tried to do this:
>
> IDL> x={blah,y:ptr_new()}
> IDL> x.y = ptrarr(4)
> % Expression must be a scalar in this context: <POINTER Array[4]>.
> % Execution halted at: $MAIN$
>
> I (mostly) knew it wouldn't work, but is there a way to do this? Having
> a pointer to a pointer array I find..... disconcerting.
>
> In the final application I would have the following procedure,
>
> PRO blah__define
> void = { blah, y:some_fancy_definition?.... }
> END
>
> and then do something like,
>
> PRO blah::allocate, n
> self.y = PTRARR(N_ELEMENTS(n)) ; This causes the heartache.
> FOR i = 0, N_ELEMENTS(n)-1 DO BEGIN
> self.y[i] = PTR_NEW(DBLARR(n[i]))
> ENDFOR
> END
>
> to be called thusly:
>
> x = obj_new('blah')
> x->allocate([2,5,9,25])
>
> Is it doable? Am I missing another simple fix (ala the
> FORMAT_AXIS_VALUES function from a previous thread :o) I would like to
> avoid the double dereferencing if possible.
>
> Hopefully I've explained myself. Thanks for making it this far.
>
> cheers,
>
> paulv
How about creating a pointer to a pointer array?
pro blah::allocate, n
compile_opt strictarr
*self.y = ptrarr(n_elements(n))
for i = 0, n_elements(n) - 1L do begin
(*self.y)[i] = ptr_new(dblarr(n[i]))
endfor
end
function blah::get, m, n
compile_opt strictarr
return, (*(*self.y)[m])[n]
end
pro blah::set, m, n, value
compile_opt strictarr
(*(*self.y)[m])[n] = value
end
function blah::init
compile_opt strictarr
self.y = ptr_new(/allocate_heap)
return, 1
end
pro blah__define
void = { blah, y: ptr_new() }
end
This could be used like:
IDL> blah = obj_new('blah')
IDL> blah->allocate, [2, 5, 9, 25]
IDL> blah->set, 1, 0, findgen(5)
IDL> print, blah->get(1, 2)
4.0000000
Mike
--
www.michaelgalloy.com
Associate Research Scientist
Tech-X Corporation
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