From bug-octave-request at bevo dot che dot wisc dot edu Fri Dec 19 15:47:31 2003
Subject: ftell - position of file pointer cannot be tested
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Schloegl Alois <alois dot schloegl at tugraz dot at>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Fri, 19 Dec 2003 15:47:26 -0600

On 19-Dec-2003, Schloegl Alois <alois dot schloegl at tugraz dot at> wrote:

| Bug report for Octave 2.1.52 configured for i686-pc-linux-gnu
| 
| Description:
| -----------
| 
| 
| fid = fopen(anyfile);
| s = fread(fid,500,'char');
| octave:4> ftell(fid)~=500
| error: binary operator `==' not implemented for `streamoff' by `scalar'
| operations
| error: evaluating binary operator `==' near line 4, column 11
| 
| ftell returns a value of type 'streamoff' which cannot be compared against a
| numeric value. In this way, ftell is pretty useless.
| 
| Is there any reason, why ftell does not return a scalar value?

Yes, because the object that is returned by the C++ stream classes to
represent file positions is no longer a long integer, and can't be
converted to one (it might not fit).  There was a short discussion
about this problem a month or two ago, I think on the
octave-maintainers mailing list.

| Repeat-By:
| ---------
| 
| fid = fopen(anyfile);
| s = fread(fid,500,'char');
| ftell(fid)==500,
| error: binary operator `==' not implemented for `streamoff' by `scalar'
| operations
| error: evaluating binary operator `==' near line 4, column 11
| 
| Fix:
| ---
| 
| ftell should return a scalar value or
| the comparison operator must handle "streamoff" data.

I think the comparision operator does handle streamoff data.  But you
are comparing a streamoff object with a scalar (double precision
number).  AFAICT, the underlying C++ objects have no way to convert
between the two, so I don't see a good way to fix this.

jwe



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