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File pointer problem on PC-IDL [message #14602]

Thu, 11 March 1999 00:00

landsman
Messages: 93
Registered: August 1991

Member

I am trying to debug a program (a "FITS" reader) that is failing on PC-IDL
Unfortunately, I don't have access to PC-IDL myself so I apologizing for not
doing as much debugging as I would have liked before posting my problem.

Basically, then internal file position is getting screwed up. I open a
binary file, readu 2880 bytes, and find myself located 4095 bytes into the
file. Below is the simple script (as done by a remote user with PC-IDL).

IDL> print, !version
{ x86 Win32 Windows 5.2 Oct 30 1998}

IDL> openr,lun,'C:\burst_image_1.fit',/block,error=error,/get_lun
IDL> if eof(lun) then message, 'Reached end of file'
IDL> buf = replicate(32b,80,36) ;Total of 2880 bytes
IDL> readu,lun,buf
IDL> help,/str,fstat(lun)
** Structure FSTAT, 12 tags, length=36:
UNIT LONG 100
NAME STRING 'C:\ROTSE\GRB 990123\burst_image_1.fit'
OPEN BYTE 1
ISATTY BYTE 0
ISAGUI BYTE 0
INTERACTIVE BYTE 0
READ BYTE 1
WRITE BYTE 0
TRANSFER_COUNT LONG 2880
CUR_PTR LONG 4095
SIZE LONG 25920
REC_LEN LONG 0

How did the current pointer get at 4095 bytes??? Calling EOF() is not
supposed to change the file position. The situation seems reminiscent of
a VMS mode where one always reads in multiple of 512 bytes. (To avoid this
problem is why the VMS-only /BLOCK keyword is added to the OPENR statement
above.) But I wasn't aware of such fixed block I/O on a PC.

Anyone have any ideas? (The file burst_image_1.fit is available at
ftp://idlastro.gsfc.nasa.gov/landsman/fits)

thanks, --Wayne Landsman landsman@mpb.gsfc.nasa.gov

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[Message index]

		File pointer problem on PC-IDL By: landsman on Thu, 11 March 1999 00:00
		Re: File pointer problem on PC-IDL By: menakkis on Thu, 18 March 1999 00:00
		Re: File pointer problem on PC-IDL By: Craig Markwardt on Thu, 18 March 1999 00:00
		Re: File pointer problem on PC-IDL By: landsman on Thu, 18 March 1999 00:00
		Re: File Pointer By: Paul Van Delst[1] on Mon, 06 December 2004 14:50
		Re: File Pointer By: David Fanning on Mon, 06 December 2004 13:28

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