From bug-octave-request at bevo dot che dot wisc dot edu Sun Jan  4 15:14:45 2004
Subject: Re: ftell - position of file pointer cannot be tested
From: Schloegl Alois <alois dot schloegl at tugraz dot at>
To: bug-octave at bevo dot che dot wisc dot edu
Date: Sun, 4 Jan 2004 14:19:06 -0600

Zitat von "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>:

> 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
>


The following patch solves the problem, at least for me. I'm using gcc 3.3.3

Alois


*** cvs/octave2/src/file-io.cc       Sun Jan  4 19:01:55 2004
--- cvs/octave/src/file-io.cc  Sun Jan  4 19:42:34 2004
***************
*** 633,639 ****
  from the beginning of the file  at var{fid} dot \n\
   at end deftypefn")
  {
!   octave_value retval = (long long) -1;

    int nargin = args.length ();

--- 633,639 ----
  from the beginning of the file  at var{fid} dot \n\
   at end deftypefn")
  {
!   octave_value retval = streamoff_array (dim_vector (1, 1), -1);

    int nargin = args.length ();

***************
*** 642,648 ****
        octave_stream os = octave_stream_list::lookup (args(0), "ftell");

        if (! error_state)
!       retval = (long long) os.tell ();
      }
    else
      print_usage ("ftell");
--- 642,648 ----
        octave_stream os = octave_stream_list::lookup (args(0), "ftell");

        if (! error_state)
!       retval = streamoff_array (dim_vector (1, 1), os.tell ());
      }
    else
      print_usage ("ftell");



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