| Changing File Size with OPENU? [message #10220] |
Mon, 27 October 1997 00:00 |
Wayne Landsman
Messages: 117
Registered: January 1997
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Senior Member |
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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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