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Re: byte offset in POINT_LUN [message #55240]

Thu, 09 August 2007 15:44

badjelly.witch
Messages: 27
Registered: May 2006

Junior Member

>> And, viola! You are back! :-)

Magniifque!

I'd just like to add a warning: jumping around in a file *may* not be
as efficient as you might think, especially if you're going backwards
from the current position. Specifically, if you have gzipped your
large ASCII file and opened it in IDL with the OPENR COMPRESS keyword
(and why wouldn't you?) then moving around with POINT_LUN involves
reinitialising the compressed data stream. I think to all intents and
purposes it means IDL goes back to the start of the file and reads up
to the saved position again.

I remember years ago I discovered a BACKSPACE command in an old
version of Fortran on a PDP 11. I wrote a program that read a line,
thought about it for a while and then backspaced to the start of the
line and reread it. It worked beautifully on a small file but bogged
down horribly on a large one, because BACKSPACE was rereading the
entire file. A valuable lesson!

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[Message index]

		Re: byte offset in POINT_LUN By: badjelly.witch on Thu, 09 August 2007 15:44
		Re: byte offset in POINT_LUN By: Josh on Wed, 08 August 2007 15:15
		Re: byte offset in POINT_LUN By: David Fanning on Wed, 08 August 2007 14:36
		Re: byte offset in POINT_LUN By: James Kuyper on Wed, 08 August 2007 14:30
		Re: byte offset in POINT_LUN By: Josh on Wed, 08 August 2007 13:05

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