comp.lang.idl-pvwave archive - RDF feed
type: channel
description: Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
items: File pointer problem on PC-IDL
items: Re: File pointer problem on PC-IDL
items: Re: File Pointer

File pointer problem on PC-IDL
type: item
description: 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
creator: landsman
date: 1999-03-11T08:00:00-00:00

Re: File pointer problem on PC-IDL
type: item
description: landsman@stars.gsfc.nasa.gov (Wayne Landsman) wrote: <...> > 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. <...> Wayne, don't ask me why, but ask your remote user to include the switch /NOAUTOMODE in the OPEN call. Oh well, it's hard to turn down any opportunity to pick on RSI for this little Windows feature of theirs. :-) It has bothered me since the day it sidled onto the scene, announced - as it were - somewhere in the bowels of the readme file. Basically IDL's I/O on Windows has a "text mode" and a "binary mode". One of these (the "binary" mode, would you believe?) fools around with <CR><LF> pairs. For some reason your EOF check is triggering IDL to switch to "binary" mode or something. (I haven't checked, but it seems unlikely to me that your file would have enough <CR><LF> pairs to fool with to account for the discrepancy - it looks more like a bug.) Another strange thing is that (in this case) if you use the /BINARY switch in the OPEN call it will also fix the problem. (I don't even want to speculate on this one.) Peter Mason -----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
creator: menakkis
date: 1999-03-18T08:00:00-00:00

Re: File pointer problem on PC-IDL
type: item
description: landsman@stars.gsfc.nasa.gov (Wayne Landsman) writes: > > ... discussion of binary files under Windows ... > On a side note, I have found that ON_IOERROR resets the file pointer, at least in reading from pipes under Unix. This was a real show-stopper until I realized what was going on, since you can't use POINT_LUN on a pipe. I had to remove my ON_IOERROR calls. Has anybody else experienced the same? Craig -- ------------------------------------------------------------ -------------- Craig B. Markwardt, Ph.D. EMAIL: craigmnet@astrog.physics.wisc.edu Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response ------------------------------------------------------------ --------------
creator: Craig Markwardt
date: 1999-03-18T08:00:00-00:00

Re: File pointer problem on PC-IDL
type: item
description: In article <7cpol7$k4h$1@nnrp1.dejanews.com>, Peter Mason <menakkis@my-dejanews.com> writes... > landsman@stars.gsfc.nasa.gov (Wayne Landsman) wrote: > <...> >> 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. > <...> > > Wayne, don't ask me why, but ask your remote user to include the switch > /NOAUTOMODE in the OPEN call. > Peter, thanks for the info. The IDL documentation certainly gives the impression that the Windows-only /NOAUTOMODE and /BINARY keywords to OPEN have an effect only when *writing* to a file. I guess my example shows that one has to be aware of flipping between "text" mode and "binary" mode, even when reading a existing file opened with OPENR. --Wayne Landsman landsman@mpb.gsfc.nasa.gov
creator: landsman
date: 1999-03-18T08:00:00-00:00

Re: File Pointer
type: item
description: Pravesh writes: > HOw do i implement a feature, that on clicking of a button will > automatically display the next file in the directory. the files are > images. Well, you just go to the next file in the list of files you are keeping, read the file, and display the image. Then you probably update your file position pointer because you always want to know where you are in your list. Cheers, David -- David Fanning, Ph.D. Fanning Software Consulting, Inc. Coyote's Guide to IDL Programming: http://www.dfanning.com/
creator: David Fanning
date: 2004-12-06T21:28:34-00:00

Re: File Pointer
type: item
description: Pravesh wrote: > Hi: > HOw do i implement a feature, that on clicking of a button will > automatically display the next file in the directory. the files are > images. Some sort of widget code that, e.g., after using findfile to get a list of the requested files (*.png or *.gif or whatever), displays the first one in the list. The button widget then just goes through the list with its event handler displaying the file. paulv -- Paul van Delst CIMSS @ NOAA/NCEP/EMC
creator: Paul Van Delst[1]
date: 2004-12-06T22:50:53-00:00