From maintainers-request at octave dot org Tue Dec 21 14:11:12 2004
Subject: feof(), ftell()
From: Daniel J Sebald <daniel dot sebald at ieee dot org>
To: octave maintainers mailing list <maintainers at octave dot org>
Date: Tue, 21 Dec 2004 14:14:56 -0600

I'm working on a block processing method where I read in data something 
like:

  while ~feof(fid)

and ran into some problems.  It is easily fixed with some other tests.  
However, the behavior of ftell() and feof() confused me a bit until I 
figured out what was going on.  Here is some sample code.  Consider if 
the results are a bit confusing.

fid = fopen('junk.dat', 'w+', 'ieee-le');
fwrite(fid, eye(2), 'int16');
fclose(fid);

fid = fopen('junk.dat', 'r+', 'ieee-le');
fseek(fid, 8, 'bof')
feof(fid)
ftell(fid)
fread(fid, 1, 'int16')
feof(fid)
ftell(fid)
fclose(fid);

fid = fopen('junk.dat', 'r+', 'ieee-le');
fseek(fid, 9, 'bof')
feof(fid)
ftell(fid)
fread(fid, 1, 'int16')
feof(fid)
ftell(fid)
fclose(fid);

What I find confusing is the last example.  I realize that the fseek() 
returns a -1, therefore THE RESULTS THAT FOLLOW DO NOT APPLY.  However, 
wouldn't it be possible for feof() to return a 1 if one positions the 
pointer past the end of file?  An 8 is past the end of the file.  Why 
should that be OK, but not 9?  Also, ftell() wrapping around in the 9 
example, is that confusing?

Thanks,

Dan