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Re: structures still confusing [message #49073 is a reply to message #49070]

Tue, 13 June 2006 07:54

btt
Messages: 345
Registered: December 2000

Senior Member

Martin Rother wrote:
> Hi Gurus,
>
> finally something, where I don't know,
> if it's odd idl syntax or not...
>
> something about structures.
>
> FUNCTION test_struct
>
> s = [{ m : [1L, 2L, 3L], n :1L }]
>
> FOR i = 1L, 2L DO BEGIN
> ;
> s = [s, { m : [1L, 2L, 3L], n : i }]
> ;
> ENDFOR
>
> return, s
>
> END
>
> this creates an array of structures:
>
> (X). s = test_struct()
> (X). help,/struct,s
> ** Structure <fa330>, 2 tags, length=16, data length=16, refs=1:
> M LONG Array[3]
> N LONG 1
> (X). print, n_elements(s)
> 3
> (X).
>
> so far ok, I guess. but
>
> (X). help,s.m
> <Expression> LONG = Array[3, 3]
> (X). print, s.m
> 1 2 3
> 1 2 3
> 1 2 3
> (X). print, s.m[0]
> 1 1 1
> (X). print, s.m[1]
> 2 2 2
> (X). print, s.m[2]
> 3 3 3
>
> is a *bit* confusing. isn't it?
>
>
> best regards,
> martin.

Hi,

Perhaps you are looking to get the entire m array of the ith element in
vector s?

IDL> s = [{ m : [1L, 2L, 3L], n :1L }]
IDL> FOR i = 1L, 2L DO s = [s, { m : [1L, 2L, 3L], n : i }]
IDL> print, s[0].m
1 2 3

Which is different than asking for the ith elements of the m array in
ALL the structures in the vector s.

IDL> print, s.m[0]
1 1 1

Or how about the ith element of the m array in the jth element of the
vector s?

IDL> print, s[0].m[0]
1

I agree it can be confusing (wait till you have pointers in there!) but
is very handy sometimes, too.

Ben

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[Message index]

		Re: structures still confusing By: JD Smith on Tue, 13 June 2006 09:33
		Re: structures still confusing By: rother on Tue, 13 June 2006 08:45
		Re: structures still confusing By: btt on Tue, 13 June 2006 07:54
		Re: structures still confusing By: Allan Whiteford on Tue, 13 June 2006 01:13
		Re: structures still confusing By: Mark Hadfield on Mon, 12 June 2006 18:42

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