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Re: Defining Integer Field in a Structure [message #27823 is a reply to message #27736]

Tue, 06 November 2001 17:30

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Harvey Rarback (rarback@slac.stanford.edu) writes:

>> If you wish to create a stucture definition without
>> actually creating an instance of a structure, you
>> put the structure definition in a file, like this:
>>
>> PRO newstruct__define.pro
>> struct = {NEWSTRUCT, a:0, b:0.0, c:fltarr(10)}
>> END
>
> This is something that has always confused me. It seems like the variable
> "struct" is created (at least help will tell you that it exists). So, does
> IDL
> "actually create an instance of a structure" with this mechanism or not?

Well, of course, I was speaking metaphorically. :-)

Certainly an instance of this structure gets created
in this routine, but its existence is fleeting. In
fact, it exists only as long as it takes to establish
the structure definition in IDL. Once that done, the
struct variable goes out of scope and the memory that
was allocated for its definition can be reused by
the real structure you are trying to create. Think
of it as smoke and mirrors.

Does that clear up the confusion?

Cheers,

David

P.S. Harvey, it is good to hear from you again. I was
afraid you had found something more productive than
IDL to do. :-)
--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Defining Integer Field in a Structure By: sailfalmouth on Thu, 01 November 2001 13:07
		Re: Defining Integer Field in a Structure By: Mark Hadfield on Tue, 06 November 2001 19:07
		Re: Defining Integer Field in a Structure By: Harvey Rarback on Tue, 06 November 2001 18:09
		Re: Defining Integer Field in a Structure By: David Fanning on Tue, 06 November 2001 17:30

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