Folks,
I believe there's a bug in the FILE_INFO function. I am running IDL
v6.4 on Linux.
I'm writing a program that does a lot of file updates and it's necessary
for me to get the current file size after an update to an open file. I
decided to use FILE_INFO rather than FSTAT because I also must first
check to see if the file exists. FILE_INFO can tell you if the file
exists as well it's size in bytes. It's also newer than FSTAT, so I
thought I'd just use FILE_INFO exclusively in my program.
Well, things just weren't making sense, and I boiled it down to this.
If I append a new record to a file and immediately check the file size
with FILE_INFO it gives me the wrong size. It returns the size BEFORE
the record was added. However, FSTAT will give the correct new size.
And, once FSTAT has been called, then FILE_INFO knows about the new
size. It's like FSTAT issues a FLUSH, because the only way FILE_INFO
gives the correct size is if FLUSH (or FSTAT) is called first. This is
fine, however there is no mention in the documentation that FLUSH must
be called first.
Below is some code to illustrate the problem:
pro file_info_vs_fstat
fname = 'test.txt'
openw, lun, /get_lun, fname
nrec = 3
for i = 0, nrec-1 do begin
print, 'Before writing record file_info.size, fstat.size:', $
(file_info( fname )).size, (fstat( lun )).size,
format='(a,1x,2i6)'
printf, lun, 'This is record number ', i
print, 'After writing record file_info.size, fstat.size:', $
(file_info( fname )).size, (fstat( lun )).size,
format='(a,1x,2i6)'
print, ' ' ; print blank line for readability
endfor
free_lun, lun
return
end
;;;;;;;;;;;;;;;; Run above procedure
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
IDL> file_info_vs_fstat
Before writing record file_info.size, fstat.size: 0 0
After writing record file_info.size, fstat.size: 0 31
Before writing record file_info.size, fstat.size: 31 31
After writing record file_info.size, fstat.size: 31 62
Before writing record file_info.size, fstat.size: 62 62
After writing record file_info.size, fstat.size: 62 93
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;
Now, if you replace the "After" print statement with the following one
that simply
reverses the order the two functions are called, you then get the
correct result from
the FILE_INFO function:
print, 'After writing record fstat.size, file_info.size:', $
(fstat( lun )).size, (file_info( fname )).size,
format='(a,1x,2i6)'
IDL> file_info_vs_fstat
Before writing record file_info.size, fstat.size: 0 0
After writing record fstat.size, file_info.size: 31 31
Before writing record file_info.size, fstat.size: 31 31
After writing record fstat.size, file_info.size: 62 62
Before writing record file_info.size, fstat.size: 62 62
After writing record fstat.size, file_info.size: 93 93
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;
Ciao,
-Dave Wuertz
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