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Re: passing structure elements... by value? [message #25809 is a reply to message #25725]

Mon, 16 July 2001 02:45

Jaco van Gorkom
Messages: 97
Registered: November 2000

Member

Randall Skelton wrote:
> I have a simple routine that increments the value of a structure:
>
> pro test, mod_struct
> for i=0, n_tags(mod_struct)-1 do begin
> mod_struct.(i) = mod_struct.(i) + 1
> endfor
> end
>
> As expected, this will increment all of the values in a passed structure.
>
> IDL> struct = {A:0, B:0} & big = replicate(struct,3)
> IDL> print, big
> { 0 0}{ 0 0}{ 0 0}
> IDL> test, big
> IDL> print, big
> { 1 1}{ 1 1}{ 1 1}
>
> But, when I try and increment a single element in the structure it fails?
>
> IDL> struct = {A:0, B:0} & big = replicate(struct,3)
> IDL> test, big[0]
> IDL> print, big
> { 0 0}{ 0 0}{ 0 0}
> ^^^^^^^^^^^^^^^^^^
>
> I expected the ^^ element above to be ones? Is there any way to force IDL
> to pass this by reference instead of passing by value? It would be nice if
> you could put brackets around the thing you want to pass by reference...
> something like '(big[0])'

Note that in your example you are passing one *array* element of an array of
structures. Indexed array elements are also passed by value - see Liam's list.
One workaround would be to copy the array element(s) into a temporary variable:
working_elements = big[range]
test, working_elements
big[range] = working_elements
, with range being a vector of indices, just [0] in the example.
Another workaround involves passing the indices-of-interest into the routine.

cheers,
Jaco

----------------
Jaco van Gorkom gorkom@rijnh.nl
FOM-Instituut voor Plasmafysica `Rijnhuizen', The Netherlands

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[Message index]

		passing structure elements... by value? By: Randall Skelton on Fri, 13 July 2001 09:03
		Re: passing structure elements... by value? By: Vince Hradil on Tue, 17 July 2001 08:54
		Re: passing structure elements... by value? By: Jaco van Gorkom on Mon, 16 July 2001 02:45
		Re: passing structure elements... by value? By: david[2] on Fri, 13 July 2001 09:53
		Re: passing structure elements... by value? By: Liam E. Gumley on Fri, 13 July 2001 09:39

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