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Re: variables in common blocks [message #53873 is a reply to message #53871]

Fri, 04 May 2007 08:16

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Lasse Clausen writes:

> Ok. I'll describe what I am using common blocks for: Whatever day
> during the week, I am doing one of the following:
> 1) read data
> 2) process data
> 3) plot data
> Since there are many different ways to process or plot data, it is
> nice to read the data into common blocks, so that when I decide to
> process or plot the data differently, I do not have to read it in
> again.
>
> If you have an easy solution on how to avoid common blocks, shoot. And
> why are common blocks bad? Is it the same reason "goto" statements are
> bad?

Oh, oh. *I* didn't want to get into it. I just wanted
to light the fire. :-(

OK, there is *nothing* inherently evil about either Common
blocks or GOTO statements. Both have a purpose, and I have
used both (I think, although I can't remember a specific
instance of either).

But what generally makes both Common blocks and GOTO
statements pernicious is how easy it is for inexperienced
programmers to substitute them for clear thinking and
well-written programs. The program I have been working
on for several weeks was brought to me because it is
nearly impossible for two "expert" users to get the program
to run the same way twice in a row, or--sometimes--to
even run at all. It depends entirely on what order things
are done and the current phase of the moon. Mostly, this
is because of the indiscriminate use of Common blocks,
and the fact that the left hand doesn't always know what the
right hand is doing.

If I saw a COMMON block in a program written by JD Smith
or Craig Markwardt, I probably wouldn't even think twice.
But when I open an e-mail and there is someone pleading for
"help" and I see Common blocks, I head straight for the
liquor cabinet.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: variables in common blocks By: David Fanning on Fri, 04 May 2007 09:48
		Re: variables in common blocks By: Christopher Thom on Fri, 04 May 2007 09:40
		Re: variables in common blocks By: David Fanning on Fri, 04 May 2007 09:03
		Re: variables in common blocks By: lasse on Fri, 04 May 2007 08:56
		Re: variables in common blocks By: Foldy Lajos on Fri, 04 May 2007 08:36
		Re: variables in common blocks By: David Fanning on Fri, 04 May 2007 08:16
		Re: variables in common blocks By: Maarten[1] on Fri, 04 May 2007 08:07
		Re: variables in common blocks By: lasse on Fri, 04 May 2007 07:42
		Re: variables in common blocks By: David Fanning on Fri, 04 May 2007 07:11
		Re: variables in common blocks By: lasse on Fri, 04 May 2007 07:06
		Re: variables in common blocks By: David Fanning on Fri, 04 May 2007 06:45

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