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losing pointers when concatenating array of structures [message #94050]

Sun, 08 January 2017 22:35

MarioIncandenza
Messages: 231
Registered: February 2005

Senior Member

Hi IDL Wizards,

That topic is a mouthful, but I haven't encountered a tricky problem like this in a while, and I wanted your help to understand what's really going on here. Here's the code sample:

for i=0,1 do begin
undefine,struct
struct=create_struct('array',ptr_new(lindgen(i+1)))
if n_elements(structarray) eq 0 then structarray=struct else structarray=[structarray,struct]
help,*structarray[i].array ; looking for error
; this is where the error will happen
if(i gt 0) then help,*structarray[i-1].array
endfor
end

Here's the result:
% Compiled module: $MAIN$.
<PtrHeapVar23543>
LONG = Array[1]
<PtrHeapVar23544>
LONG = Array[2]
% Invalid pointer: <POINTER (<PtrHeapVar23543>)>.
% Execution halted at: $MAIN$ 9

Here's the fix:
if n_elements(structarray) eq 0 then structarray=temporary(struct) else structarray=[structarray,temporary(struct)]

If you use TEMPORARY(), this works. If you do not, it fails. Can someone help me understand this?

Happy New Year's everyone,

--Edward H.

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[Message index]

		losing pointers when concatenating array of structures By: MarioIncandenza on Sun, 08 January 2017 22:35
		Re: losing pointers when concatenating array of structures By: Heinz Stege on Mon, 09 January 2017 02:10
		Re: losing pointers when concatenating array of structures By: MarioIncandenza on Mon, 09 January 2017 08:44
		Re: losing pointers when concatenating array of structures By: Jim Pendleton on Mon, 09 January 2017 11:05
		Re: losing pointers when concatenating array of structures By: Heinz Stege on Mon, 09 January 2017 12:33

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