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Re: pointer to structures [message #19564 is a reply to message #19558]

Tue, 04 April 2000 00:00

John-David T. Smith is currently offline

John-David T. Smith
Messages: 384
Registered: January 2000

Senior Member

"Liam E.Gumley" wrote:
>
> eeeyler@my-deja.com wrote:
>> suppose I wish to create a structure and wish to reference that
>> structure and its contents via a pointer:
>> filter=ptr_new({points:['a','b'],pt1_value:200, pt2_value:'X_WHYLOG'})
>> how do I reference the points array? I thought it would be as:
>> print, *filter.points
>> but I get the message
>> %Expression must be a structure in this context: Filter
>
> ptr = ptr_new({test:indgen(10)})
> print, (*ptr).test
> 0 1 2 3 4 5 6 7
> 8 9
>
> If you want to keep it really simple and clean, separate the pointer
> de-reference and the structure reference:
>
> struct = *ptr
> print, struct.test
>
> This can make your code much more understandable when multiple levels of
> de-referencing are required (say if the structure contains a pointer to
> an array).

With time, you will get used to these semantics. They seem arcane, but
eventually it becomes somewhat readable to the experienced eye. Of course, I've
struggled with statements like:

HEADER=*(*(*self.DR)[sel[i]].HEADER)

but you eventually get the hang of it.

JD

--
J.D. Smith |*| WORK: (607) 255-5842
Cornell University Dept. of Astronomy |*| (607) 255-6263
304 Space Sciences Bldg. |*| FAX: (607) 255-5875
Ithaca, NY 14853 |*|

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[Message index]

		Re: pointer to structures By: John-David T. Smith on Wed, 05 April 2000 00:00
		Re: pointer to structures By: Liam E. Gumley on Wed, 05 April 2000 00:00
		Re: pointer to structures By: John-David T. Smith on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Liam E. Gumley on Tue, 04 April 2000 00:00
		Re: pointer to structures By: davidf on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Ben Tupper on Tue, 04 April 2000 00:00
		Re: pointer to structures By: John-David T. Smith on Tue, 04 April 2000 00:00
		Re: pointer to structures By: John-David T. Smith on Tue, 04 April 2000 00:00
		Re: pointer to structures By: davidf on Tue, 04 April 2000 00:00
		Re: pointer to structures By: wbiagiot on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Liam E. Gumley on Tue, 04 April 2000 00:00
		Re: pointer to structures By: Ben Tupper on Tue, 04 April 2000 00:00

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