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Re: Changing File Size with OPENU? [message #10210 is a reply to message #10203]

Tue, 28 October 1997 00:00

Jack Saba
Messages: 30
Registered: January 1996

Member

I get the same behavior under both IDL 4 and IDL 5.0.2. However, when I
removed the READU, and changed the point_lun to

POINT_LUN, LUN, 14400+2400

the final file size was the same as the initial file size.

--
Jack Saba <jack@magus.stx.com>

Wayne Landsman wrote:
>
> I always thought that when opening a file with OPENU that the file
> wouldn't
> change size, unless one wrote past the end of the file. But below I
> give an
> example of a file changing size, even though I never reached the end of
> the
> file.
>
> I suspect this might be a IDL (or Solaris 2.6) bug, because if I
> uncomment the
> ;print,fstat(lun) line below, then the file size stays unchanged. But
> I
> don't trust my thought process right now after spending 3 hours trying
> to track
> down this bug. Anybody know if the behaviour in the example below is
> expected?
>
> --Wayne Landsman
> landsman@mpb.gsfc.nasa.gov
>
> ; IDL Version 5.0.2 (sunos sparc)
>
> ;Create a 250000 byte file
>
> openw,lun,'tester.dat',/get_lun
> writeu,lun,bytarr(250000)
> close,lun
>
> ;Make sure it really is 250000 bytes
>
> spawn,'ls -l tester.dat'
> ;-rw-r--r-- 1 landsman 250000 Oct 26 08:13 tester.dat
>
> ;Now open file for update and move
> ; 14400 + 2400 + 230000 = 246800 bytes into the file
>
> openu,lun,'tester.dat'
> point_lun,lun,14400 ;Offset to 14400 bytes
> b = bytarr(2400)
> readu,lun,b ;Now read 2400 bytes
> ;print,fstat(lun)
> writeu,lun,bytarr(230000) ;Now write 230000 bytes
> free_lun,lun
> spawn,'ls -l tester.dat' ;And file has changed size!!
>
> -rw-r--r-- 1 landsman 254992 Oct 26 08:13 tester.dat

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[Message index]

		Re: Changing File Size with OPENU? By: Peter Mason on Tue, 28 October 1997 00:00
		Re: Changing File Size with OPENU? By: Jack Saba on Tue, 28 October 1997 00:00
		Re: Changing File Size with OPENU? By: Peter Mason on Tue, 28 October 1997 00:00
		Re: Changing File Size with OPENU? By: Wayne Landsman on Mon, 27 October 1997 00:00
		Re: Changing File Size with OPENU? By: thompson on Mon, 27 October 1997 00:00

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