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Re: pointer to structures [message #19565 is a reply to message #19558]

Tue, 04 April 2000 00:00

davidf
Messages: 2866
Registered: September 1996

Senior Member

eeeyler@my-deja.com (eeeyler@my-deja.com) writes:

> 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

The problem here is that a pointer dereference has the lowest
order of precedence. Lower, even, than a structure dereference.
So, you must first dereference the structure (by using
parentheses), and *then* dereference the pointer, like this:

filter=ptr_new({points:['a','b'],pt1_value:200, pt2_value:'X_WHYLOG'})
Print, *(filter.points)

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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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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