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Re: Write to a certain line of a file [message #78956]

Thu, 19 January 2012 11:02

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Michael Galloy writes:

> You are essentially treating the file as a binary file where you have
> more options, but also more responsibility for keeping things straight.
>
> Sure, this would work in the case where the new output has the exact
> same length in bytes as the old output, but if not everything is going
> to get screwed up. You could rewrite the file after the point of
> insertion to fix this, but how much is it worth it to get around writing
> this file?

I was curious how long it would take to re-write a 10000 line ASCII file
after replacing a line in it. Answer: 0.014 seconds!

Here is the code I used.

;----------------------------------------------------------- ----
; Create a random set of strings.
LENGTH=10000
len = Round(Scale_Vector(Randomu(-3L, LENGTH), 10, 60))
file = StrArr(LENGTH)
FOR j=0,N_Elements(len)-1 DO BEGIN
str = Byte(Scale_Vector(RandomU(seed, len[j]), 97, 122))
space = Fix(randomu(seed, len[j]/5 > 1) * len[j] > 2)
str[space] = 32B
file[j] = String(str)
ENDFOR

; Write the random strings to a file.
OpenW, lun, 'test_ascii_file.txt', /Get_Lun
FOR j=0, LENGTH-1 DO PrintF, lun, file[j]
Free_Lun, lun

; Replace line 50 with 'The dog ate my homework!'
start = Systime(1)
lines = File_Lines('test_ascii_file.txt')
OpenR, lun, 'test_ascii_file.txt', /Get_Lun
strings = StrArr(lines)
strings[49] = 'The dog ate my homework!'
Free_Lun, lun

OpenW, lun, 'test_ascii_file_1.txt'
FOR j=0,N_Elements(strings)-1 DO PrintF, lun, strings[j]
Free_Lun, lun
Print, 'Time to rewrite file: ', systime(1) - start

END
;---------------------------------------------------

Cheers,

David

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

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[Message index]

		Re: Write to a certain line of a file By: David Fanning on Thu, 19 January 2012 11:02
		Re: Write to a certain line of a file By: Michael Galloy on Thu, 19 January 2012 09:49
		Re: Write to a certain line of a file By: Mark Piper on Thu, 19 January 2012 08:43
		Re: Write to a certain line of a file By: Brian Daniel on Thu, 19 January 2012 04:18
		Re: Write to a certain line of a file By: Brian Wolven on Wed, 18 January 2012 18:02
		Re: Write to a certain line of a file By: Matt Francis on Wed, 18 January 2012 17:16
		Re: Write to a certain line of a file By: Michael Galloy on Wed, 18 January 2012 12:08
		Re: Write to a certain line of a file By: natha on Wed, 18 January 2012 12:05
		Re: Write to a certain line of a file By: Mark Piper on Fri, 20 January 2012 08:21

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