[Octave-bug-tracker] [bug #49820] fseek fails for large (>4GByte files)

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?49820>

                 Summary: fseek fails for large (>4GByte files)
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sat 10 Dec 2016 01:07:15 PM UTC
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Pat Gioannini
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.0
        Operating System: GNU/Linux

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Details:

In file_io.cc the function for fseek contains the code:



DEFUN (fseek, args, ,
       doc: /* -*- texinfo -*-
@deftypefn  {} {} fseek (@var{fid}, @var{offset})
@deftypefnx {} {} fseek (@var{fid}, @var{offset}, @var{origin})
@deftypefnx {} address@hidden =} fseek (@dots{})
Set the file pointer to the location @var{offset} within the file @var{fid}.

The pointer is positioned @var{offset} characters from the @var{origin},
which may be one of the predefined variables @address@hidden (current
position), @address@hidden (beginning), or @address@hidden (end of
file) or strings @qcode{"cof"}, @qcode{"bof"} or @qcode{"eof"}.  If
@var{origin} is omitted, @address@hidden is assumed.  @var{offset} may
be positive, negative, or zero but not all combinations of @var{origin} and
@var{offset} can be realized.

@code{fseek} returns 0 on success and -1 on error.
@seealso{fskipl, frewind, ftell, fopen}
@end deftypefn */)
{
  int nargin = args.length ();

  if (nargin < 2 || nargin > 3)
    print_usage ();

  octave_stream os = octave_stream_list::lookup (args(0), "fseek");

  octave_value origin_arg = (nargin == 3) ? args(2) : octave_value (-1.0);

  return ovl (os.seek (args(1), origin_arg));
}
--

The conversion from octave_value in the last line converts args(1) to an int
(32bits) rather than an off_t (64 bits).  I changed the last two lines of code
to be:

++
  off_t offset = args(1).int64_value();
  return ovl (os.seek (offset, origin_arg));
--

I am not familiar enough with octal_value to know if this is really the best
solution.  However you must treat the offset parameter as a 64 bit (off_t)
rather than 32 bits for fseek to work properly.




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