| Is a dynamically sized pointer array object component possible? [message #66554] |
Thu, 21 May 2009 14:35 |
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Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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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
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