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Re: Structures [message #42908 is a reply to message #23873]

Wed, 02 March 2005 07:33

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

m_schellens@hotmail.com wrote:
> IDL> s={s,s:indgen(42)}
> IDL> ss=[s,s,s,s]
> IDL> help,ss[*].s
> <Expression> INT = Array[42, 4]
>
> Thats why they need to be fixed size.

Why's that? Doesn't it depend on what you want to do/how flexible you want the code to be?

IDL> s={s,s:ptr_new()}
IDL> ss=[s,s,s,s]
IDL> help, ss[*].s
<Expression> POINTER = Array[4]
IDL> ss[0].s=ptr_new(indgen(731))
IDL> ss[1].s=ptr_new(indgen(20))
IDL> ss[2].s=ptr_new(indgen(5))
IDL> ss[3].s=ptr_new(indgen(7))
IDL> help, *(ss[0].s)
<PtrHeapVar1> INT = Array[731]
IDL> help, *(ss[2].s)
<PtrHeapVar3> INT = Array[5]

Granted, the way you access all the bits and pieces has become more complex due to the
pointer dereferencing, but you wouldn't do all this stuff on the command line anyway.
(Right? Like objects. :o)

And, if I was doing it the way you suggested, I wouldn't access the data in ss[*].s as a
rank-2 array, e.g.

IDL> help, (ss.s)[20,3]
<Expression> INT = 20

to get the 21st element from the 4th structure. I would reference it as

IDL> help, ss[3].s[20]
<Expression> INT = 20

My personal preference only of course. Doing it the first way seems sneaky

paulv

p.s. As an aside - in this context, this is another reason I like Fortran90/95 pointers.
The dereferencing is implicit (i.e. no "*" out the front) so your accessing code doesn't
have to change when you modify your structure to use allocatable pointers rather than
fixed size arrays. E.g. in f95, ss(3)%s(20) gets the same info whether or not the "s"
component is a fixed size array or a pointer in it's definition.

--
Paul van Delst
CIMSS @ NOAA/NCEP/EMC

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[Message index]

		Structures: By: Chris Bull on Wed, 21 February 2001 11:15
		Re: Structures By: marc schellens[1] on Wed, 02 March 2005 19:14
		Re: Structures By: David Fanning on Wed, 02 March 2005 09:36
		Re: Structures By: Benjamin Hornberger on Wed, 02 March 2005 09:33
		Re: Structures By: Paul Van Delst[1] on Wed, 02 March 2005 09:31
		Re: Structures By: Michael Wallace on Wed, 02 March 2005 09:04
		Re: Structures By: Michael Wallace on Wed, 02 March 2005 08:59
		Re: Structures By: Paul Van Delst[1] on Wed, 02 March 2005 07:33
		Re: Structures By: marc schellens[1] on Tue, 01 March 2005 19:43
		Re: Structures By: David Fanning on Tue, 01 March 2005 16:49
		Re: Structures By: Michael Wallace on Tue, 01 March 2005 16:40
		Re: Structures By: mperrin+news on Tue, 01 March 2005 16:21
		Re: Structures By: Paul Van Delst[1] on Tue, 01 March 2005 14:39
		Re: Structures By: Michael Wallace on Tue, 01 March 2005 14:38
		Re: Structures By: David Fanning on Tue, 01 March 2005 13:52

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