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Re: resizing system variable [message #82570 is a reply to message #82569]

Thu, 20 December 2012 20:33

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Thursday, December 20, 2012 4:44:37 PM UTC-5, astrobo...@gmail.com wrote:
> On Thursday, December 20, 2012 3:28:45 PM UTC-5, Craig Markwardt wrote:
>> It sounds to me you are trying to use a system variable like a common block (i.e. global variable). See if you an rethink how you do it without a system variable, because it will probably come back to bite you.
...
> I have a program that I call in nearly every program I write, that defines about one hundred global variables, such as the date, time, working directory, default color table, etc., using the defsysv command. In any given program I'd use only a handful of these, but I wouldn't necessarily know which ones until the program was finished.
>
> Based on David's books, it seems to me that using a common block in such a case would be a real pain.

Actually, I think that David would argue that system variables are inappropriate for use as global variables for exactly the same reason as common blocks. Global variables can pin you down in painful ways when you try to scale/enhance your program.

[ Don't tell David I mentioned this, but common blocks are actually more flexible than system variables because common block variables can be redefined - even redimensioned whenever you wish. ]

You've got a system that works, I would stick with it now.

When designing a new system, I usually define a structure with all of those quantities and then pass that structure around.

[ Actually, if I were designing my IDL library from scratch, I would start with Python. :-]

Craig

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[Message index]

		Re: resizing system variable By: Paul Van Delst[1] on Fri, 21 December 2012 08:29
		Re: resizing system variable By: Craig Markwardt on Thu, 20 December 2012 22:50
		Re: resizing system variable By: David Fanning on Thu, 20 December 2012 21:06
		Re: resizing system variable By: Craig Markwardt on Thu, 20 December 2012 20:33
		Re: resizing system variable By: David Fanning on Thu, 20 December 2012 15:14
		Re: resizing system variable By: astroboy.20000 on Thu, 20 December 2012 13:44
		Re: resizing system variable By: Craig Markwardt on Thu, 20 December 2012 12:28

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