dlmread.cc

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////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2008-2023 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Octave is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
//
////////////////////////////////////////////////////////////////////////
 
// Adapted from previous version of dlmread.occ as authored by Kai
// Habel, but core code has been completely re-written.
 
#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif
 
#include <clocale>
#include <cmath>
#include <cctype>
#include <fstream>
#include <limits>
 
#include "file-ops.h"
#include "lo-ieee.h"
#include "lo-sysdep.h"
 
#include "defun.h"
#include "interpreter.h"
#include "oct-stream.h"
#include "error.h"
#include "ovl.h"
#include "utils.h"
 
static const octave_idx_type idx_max
  = std::numeric_limits<octave_idx_type>::max () - 1;
 
static const double idx_max_dbl = double (idx_max);
 
static bool
read_cell_spec (std::istream& is, octave_idx_type& row, octave_idx_type& col)
{
  bool stat = false;
 
  if (is.peek () == std::istream::traits_type::eof ())
    stat = true;
  else
    {
      if (::isalpha (is.peek ()))
        {
          col = 0;
          while (is && ::isalpha (is.peek ()))
            {
              char ch = is.get ();
              col *= 26;
              if (ch >= 'a')
                col += ch - 'a' + 1;
              else
                col += ch - 'A' + 1;
            }
          col--;
 
          if (is)
            {
              is >> row;
              row--;
              if (is)
                stat = true;
            }
        }
    }
 
  return stat;
}
 
static bool
parse_range_spec (const octave_value& range_spec,
                  octave_idx_type& rlo, octave_idx_type& clo,
                  octave_idx_type& rup, octave_idx_type& cup)
{
  bool stat = true;
 
  if (range_spec.is_string ())
    {
      std::istringstream is (range_spec.string_value ());
      char ch = is.peek ();
 
      if (ch == '.' || ch == ':')
        {
          rlo = 0;
          clo = 0;
          ch = is.get ();
          if (ch == '.')
            {
              ch = is.get ();
              if (ch != '.')
                stat = false;
            }
        }
      else
        {
          stat = read_cell_spec (is, rlo, clo);
 
          if (stat)
            {
              ch = is.peek ();
 
              if (ch == '.' || ch == ':')
                {
                  ch = is.get ();
                  if (ch == '.')
                    {
                      ch = is.get ();
                      if (! is || ch != '.')
                        stat = false;
                    }
 
                  rup = idx_max;
                  cup = idx_max;
                }
              else
                {
                  rup = rlo;
                  cup = clo;
                  if (! is || ! is.eof ())
                    stat = false;
                }
            }
        }
 
      if (stat && is && ! is.eof ())
        stat = read_cell_spec (is, rup, cup);
 
      if (! is || ! is.eof ())
        stat = false;
    }
  else if (range_spec.is_real_matrix () && range_spec.numel () == 4)
    {
      NDArray range (range_spec.array_value ());
      if (range.any_element_is_nan ())
        error ("dlmread: NaN is not a valid row or column specifier");
 
      // double --> unsigned int avoiding any overflow
      rlo = static_cast<octave_idx_type> (std::min (range(0), idx_max_dbl));
      clo = static_cast<octave_idx_type> (std::min (range(1), idx_max_dbl));
      rup = static_cast<octave_idx_type> (std::min (range(2), idx_max_dbl));
      cup = static_cast<octave_idx_type> (std::min (range(3), idx_max_dbl));
    }
  else
    stat = false;
 
  return stat;
}
 
OCTAVE_BEGIN_NAMESPACE(octave)
 
DEFMETHOD (dlmread, interp, args, ,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{data} =} dlmread (@var{file})
@deftypefnx {} {@var{data} =} dlmread (@var{file}, @var{sep})
@deftypefnx {} {@var{data} =} dlmread (@var{file}, @var{sep}, @var{r0}, @var{c0})
@deftypefnx {} {@var{data} =} dlmread (@var{file}, @var{sep}, @var{range})
@deftypefnx {} {@var{data} =} dlmread (@dots{}, "emptyvalue", @var{EMPTYVAL})
Read numeric data from the text file @var{file} which uses the delimiter
@var{sep} between data values.
 
If @var{sep} is not defined the separator between fields is determined from
the file itself.
 
The optional scalar arguments @var{r0} and @var{c0} define the starting row
and column of the data to be read.  These values are indexed from zero,
i.e., the first data row corresponds to an index of zero.
 
The @var{range} parameter specifies exactly which data elements are read.
The first form of the parameter is a 4-element vector containing the upper
left and lower right corners @code{[@var{R0},@var{C0},@var{R1},@var{C1}]}
where the indices are zero-based.  To specify the last column---the equivalent
of @code{end} when indexing---use the specifier @code{Inf}.  Alternatively, a
spreadsheet style form such as @qcode{"A2..Q15"} or @qcode{"T1:AA5"} can be
used.  The lowest alphabetical index @qcode{'A'} refers to the first column.
The lowest row index is 1.
 
@var{file} should be a filename or a file id given by @code{fopen}.  In the
latter case, the file is read until end of file is reached.
 
The @qcode{"emptyvalue"} option may be used to specify the value used to
fill empty fields.  The default is zero.  Note that any non-numeric values,
such as text, are also replaced by the @qcode{"emptyvalue"}.
@seealso{csvread, textscan, dlmwrite}
@end deftypefn */)
{
  int nargin = args.length ();
 
  double empty_value = 0.0;
 
  if (nargin > 2 && args(nargin-2).is_string ()
      && args(nargin-2).string_value () == "emptyvalue")
    {
      empty_value = args(nargin-1).double_value ();
 
      nargin -= 2;
    }
 
  if (nargin < 1 || nargin > 4)
    print_usage ();
 
  std::istream *input = nullptr;
  std::ifstream input_file;
 
  if (args(0).is_string ())
    {
      // Filename.
      std::string fname (args(0).string_value ());
 
      std::string tname = sys::file_ops::tilde_expand (fname);
 
      tname = find_data_file_in_load_path ("dlmread", tname);
 
#if defined (OCTAVE_USE_WINDOWS_API)
      std::wstring wname = sys::u8_to_wstring (tname);
      input_file.open (wname.c_str (), std::ios::in);
#else
      input_file.open (tname.c_str (), std::ios::in);
#endif
 
      if (! input_file)
        error ("dlmread: unable to open file '%s'", fname.c_str ());
 
      input = &input_file;
    }
  else if (args(0).is_scalar_type ())
    {
      stream_list& streams = interp.get_stream_list ();
 
      stream is = streams.lookup (args(0), "dlmread");
 
      input = is.input_stream ();
 
      if (! input)
        error ("dlmread: stream FILE not open for input");
    }
  else
    error ("dlmread: FILE argument must be a string or file id");
 
  // Set default separator.
  std::string sep;
  if (nargin > 1)
    {
      if (args(1).is_sq_string ())
        sep = do_string_escapes (args(1).string_value ());
      else
        sep = args(1).string_value ();
    }
 
  // Take a subset if a range was given.
  octave_idx_type r0 = 0;
  octave_idx_type c0 = 0;
  octave_idx_type r1 = idx_max;
  octave_idx_type c1 = idx_max;
  if (nargin > 2)
    {
      if (nargin == 3)
        {
          if (! parse_range_spec (args(2), r0, c0, r1, c1))
            error ("dlmread: error parsing RANGE");
        }
      else if (nargin == 4)
        {
          r0 = args(2).idx_type_value ();
          c0 = args(3).idx_type_value ();
        }
 
      if (r0 < 0 || c0 < 0)
        error ("dlmread: left (R0) and top (C0) must be positive");
 
      // Short-circuit and return if range is empty
      if (r1 < r0 || c1 < c0)
        return ovl (Matrix (0, 0));
    }
 
  octave_idx_type i = 0;
  octave_idx_type j = 0;
  octave_idx_type r = 1;
  octave_idx_type c = 1;
  // Start with a reasonable size to avoid constant resizing of matrix.
  octave_idx_type rmax = 32;
  octave_idx_type cmax = 0;
 
  Matrix rdata (rmax, cmax, empty_value);
  ComplexMatrix cdata;
 
  bool iscmplx = false;
  bool sep_is_wspace = (sep.find_first_of (" \t") != std::string::npos);
  bool auto_sep_is_wspace = false;
 
  if (r0 == 0)
    {
      // Peek into stream and potentially strip Byte Order Mark (BOM)
      const char BOM[3] = {'\xEF', '\xBB', '\xBF'};
      char buf[3];
      int i_bom;
      bool found_bom = true;
      for (i_bom = 0; i_bom < 3; i_bom++)
        {
          char ch_p = input->peek ();
          if (ch_p == BOM[i_bom])
            buf[i_bom] = input->get ();
          else
            {
              found_bom = false;
              break;
            }
        }
      // Put back read characters if it wasn't a BOM
      if (! found_bom)
        {
          for (int i_ret = i_bom-1; i_ret >= 0; i_ret--)
            input->putback (buf[i_ret]);
        }
    }
 
  // Set "C" locale for the remainder of this function to avoid the performance
  // panelty of frequently switching the locale when reading floating point
  // values from the stream.
  char *prev_locale = std::setlocale (LC_ALL, nullptr);
  std::string old_locale (prev_locale ? prev_locale : "");
  std::setlocale (LC_ALL, "C");
  unwind_action act
  ([old_locale] () { std::setlocale (LC_ALL, old_locale.c_str ()); });
 
  std::string line;
 
  // Skip the r0 leading lines
  octave_idx_type rcnt = r0;
  while (rcnt > 0 && getline (*input, line))
    rcnt--;
 
  if (rcnt > 0)
    return ovl (Matrix (0, 0)); // Not enough lines in file to satisfy RANGE
  else
    r1 -= r0;
 
  std::istringstream tmp_stream;
 
  // Read the data one field at a time, growing the data matrix as needed.
  while (getline (*input, line))
    {
      // Skip blank lines for compatibility.
      if ((! sep_is_wspace || auto_sep_is_wspace)
          && line.find_first_not_of (" \t") == std::string::npos)
        continue;
 
      // Infer separator from file if delimiter is blank.
      if (sep.empty ())
        {
          // Skip leading whitespace.
          std::size_t pos1 = line.find_first_not_of (" \t");
 
          // For Matlab compatibility, blank delimiter should
          // correspond to whitespace (space and tab).
          std::size_t n = line.find_first_of (",:; \t", pos1);
          if (n == std::string::npos)
            {
              sep = " \t";
              auto_sep_is_wspace = true;
            }
          else
            {
              char ch = line.at (n);
 
              switch (line.at (n))
                {
                case ' ':
                case '\t':
                  sep = " \t";
                  auto_sep_is_wspace = true;
                  break;
 
                default:
                  sep = ch;
                  break;
                }
            }
        }
 
      // Estimate the number of columns from first line of data.
      if (cmax == 0)
        {
          std::size_t pos1, pos2;
          if (auto_sep_is_wspace)
            pos1 = line.find_first_not_of (" \t");
          else
            pos1 = 0;
 
          do
            {
              pos2 = line.find_first_of (sep, pos1);
 
              if (auto_sep_is_wspace && pos2 != std::string::npos)
                {
                  // Treat consecutive separators as one.
                  pos2 = line.find_first_not_of (sep, pos2);
                  if (pos2 != std::string::npos)
                    pos2 -= 1;
                }
 
              // Separator followed by EOL doesn't generate extra column
              if (pos2 != std::string::npos)
                cmax++;
 
              pos1 = pos2 + 1;
            }
          while (pos2 != std::string::npos);
 
          // FIXME: Should always be the case that iscmplx == false.
          //        Flag is initialized that way and no data has been read.
          if (iscmplx)
            cdata.resize (rmax, cmax, empty_value);
          else
            rdata.resize (rmax, cmax, empty_value);
        }
 
      r = (r > i + 1 ? r : i + 1);
      j = 0;
 
      std::size_t pos1, pos2;
      if (auto_sep_is_wspace)
        pos1 = line.find_first_not_of (" \t");  // Skip leading whitespace.
      else
        pos1 = 0;
 
      do
        {
          octave_quit ();
 
          pos2 = line.find_first_of (sep, pos1);
          std::string str = line.substr (pos1, pos2 - pos1);
 
          if (auto_sep_is_wspace && pos2 != std::string::npos)
            {
              // Treat consecutive separators as one.
              pos2 = line.find_first_not_of (sep, pos2);
              if (pos2 != std::string::npos)
                pos2 -= 1;
              else
                pos2 = line.length () - 1;
            }
 
          // Separator followed by EOL doesn't generate extra column
          if (pos2 == std::string::npos && str.empty ())
            break;
 
          c = (c > j + 1 ? c : j + 1);
          if (r > rmax || c > cmax)
            {
              // Use resize_and_fill for the case of unequal length rows.
              // Keep rmax a power of 2.
              rmax = std::max (2*(r-1), rmax);
              cmax = std::max (c, cmax);
              if (iscmplx)
                cdata.resize (rmax, cmax, empty_value);
              else
                rdata.resize (rmax, cmax, empty_value);
            }
 
          tmp_stream.str (str);
          tmp_stream.clear ();
 
          double x = read_value<double> (tmp_stream);
          if (tmp_stream)
            {
              if (tmp_stream.eof ())
                {
                  if (iscmplx)
                    cdata(i, j++) = x;
                  else
                    rdata(i, j++) = x;
                }
              else
                {
                  int next_char = tmp_stream.peek ();
                  if (next_char == 'i' || next_char == 'j'
                      || next_char == 'I' || next_char == 'J')
                    {
                      // Process pure imaginary numbers.
                      tmp_stream.get ();
                      next_char = tmp_stream.peek ();
                      if (next_char == std::istringstream::traits_type::eof ())
                        {
                          if (! iscmplx)
                            {
                              iscmplx = true;
                              cdata = ComplexMatrix (rdata);
                            }
 
                          cdata(i, j++) = Complex (0, x);
                        }
                      else
                        {
                          // Parsing failed, <number>i|j<extra text>
                          j++;  // Leave data initialized to empty_value
                        }
                    }
                  else if (std::isalpha (next_char) && ! std::isfinite (x))
                    {
                      // Parsing failed, <Inf|NA|NaN><extra text>
                      j++;  // Leave data initialized to empty_value
                    }
                  else
                    {
                      double y = read_value<double> (tmp_stream);
 
                      if (! iscmplx && y != 0.0)
                        {
                          iscmplx = true;
                          cdata = ComplexMatrix (rdata);
                        }
 
                      if (iscmplx)
                        cdata(i, j++) = Complex (x, y);
                      else
                        rdata(i, j++) = x;
                    }
                }
            }
          else
            {
              // read_value<double>() parsing failed
              j++;  // Leave data initialized to empty_value
            }
 
          pos1 = pos2 + 1;
        }
      while (pos2 != std::string::npos);
 
      if (i == r1)
        break;  // Stop early if the desired range has been read.
 
      i++;
    }
 
  // Clip selection indices to actual size of data
  if (r1 >= r)
    r1 = r - 1;
  if (c1 >= c)
    c1 = c - 1;
 
  if (iscmplx)
    {
      if ((i == 0 && j == 0) || (c0 > c1))
        return ovl (ComplexMatrix (0, 0));
 
      cdata = cdata.extract (0, c0, r1, c1);
      return ovl (cdata);
    }
  else
    {
      if ((i == 0 && j == 0) || (c0 > c1))
        return ovl (Matrix (0, 0));
 
      rdata = rdata.extract (0, c0, r1, c1);
      return ovl (rdata);
    }
}
 
/*
%!test
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1, 2, 3\n4, 5, 6\n7, 8, 9\n10, 11, 12");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2, 3; 4, 5, 6; 7, 8, 9;10, 11, 12]);
%!   assert (dlmread (file, ","), [1, 2, 3; 4, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", [1, 0, 2, 1]), [4, 5; 7, 8]);
%!   assert (dlmread (file, ",", "B1..C2"), [2, 3; 5, 6]);
%!   assert (dlmread (file, ",", "B1:C2"), [2, 3; 5, 6]);
%!   assert (dlmread (file, ",", "..C2"), [1, 2, 3; 4, 5, 6]);
%!   assert (dlmread (file, ",", 0, 1), [2, 3; 5, 6; 8, 9; 11, 12]);
%!   assert (dlmread (file, ",", "B1.."), [2, 3; 5, 6; 8, 9; 11, 12]);
%!   assert (dlmread (file, ",", 10, 0), []);
%!   assert (dlmread (file, ",", 0, 10), []);
%!   fail ('dlmread (file, ",", [0 1])', "error parsing RANGE");
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
%!testif ; ! ismac ()
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1, 2, 3\n4+4i, 5, 6\n7, 8, 9\n10, 11, 12");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2, 3; 4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ","), [1,2,3; 4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", [1, 0, 2, 1]), [4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", "A2..B3"), [4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", "A2:B3"), [4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", "..B3"), [1, 2; 4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", 1, 0), [4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", "A2.."), [4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", 10, 0), []);
%!   assert (dlmread (file, ",", 0, 10), []);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
%!test <47413>
%! ## Same test code as above, but intended only for test statistics on Mac.
%! if (! ismac ()), return; endif
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1, 2, 3\n4+4i, 5, 6\n7, 8, 9\n10, 11, 12");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2, 3; 4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ","), [1,2,3; 4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", [1, 0, 2, 1]), [4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", "A2..B3"), [4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", "A2:B3"), [4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", "..B3"), [1, 2; 4 + 4i, 5; 7, 8]);
%!   assert (dlmread (file, ",", 1, 0), [4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", "A2.."), [4 + 4i, 5, 6; 7, 8, 9; 10, 11, 12]);
%!   assert (dlmread (file, ",", 10, 0), []);
%!   assert (dlmread (file, ",", 0, 10), []);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
%!test <*42025>
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "    \n 1 2\n11 22\n ");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2; 11, 22]);
%!   assert (dlmread (file, " "), [ 0,  0, 0, 0
%!                                  0,  1, 2, 0
%!                                 11, 22, 0, 0
%!                                  0,  0, 0, 0]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
%!testif ; ! ismac ()   <*50589>
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1;2;3\n");
%!   fwrite (fid, "1i;2I;3j;4J\n");
%!   fwrite (fid, "4;5;6\n");
%!   fwrite (fid, "-4i;+5I;-6j;+7J\n");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2, 3, 0; 1i, 2i, 3i, 4i;
%!                            4, 5, 6, 0; -4i, 5i, -6i, 7i]);
%!   assert (dlmread (file, "", [0 0 0 3]), [1, 2, 3]);
%!   assert (dlmread (file, "", [1 0 1 3]), [1i, 2i, 3i, 4i]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
%!test <47413>
%! ## Same test code as above, but intended only for test statistics on Mac.
%! if (! ismac ()), return; endif
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1;2;3\n");
%!   fwrite (fid, "1i;2I;3j;4J\n");
%!   fwrite (fid, "4;5;6\n");
%!   fwrite (fid, "-4i;+5I;-6j;+7J\n");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2, 3, 0; 1i, 2i, 3i, 4i;
%!                            4, 5, 6, 0; -4i, 5i, -6i, 7i]);
%!   assert (dlmread (file, "", [0 0 0 3]), [1, 2, 3]);
%!   assert (dlmread (file, "", [1 0 1 3]), [1i, 2i, 3i, 4i]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
## NA was not properly read from a file
%!test
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1,NA,3");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, NA, 3]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
## "Name" was read as NA rather than parse error
%!test <*54029>
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "NaNe,bNa,Name,c\n1,NaN,3,Inftest\n-Inf,6,NA,8");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [0, 0, 0, 0; 1, NaN, 3, 0; -Inf, 6, NA, 8]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
## Infinity incorrectly changed matrix to complex, rather than parse error
%!test
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1,Infinity,3");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 0, 3]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
## Purely complex numbers with trailing garbage produced complex matrix
%!test
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, "1,2jack,3");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 0, 3]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
## Verify UTF-8 Byte Order Mark does not cause problems with reading
%!test <*58813>
%! file = tempname ();
%! unwind_protect
%!   fid = fopen (file, "wt");
%!   fwrite (fid, char ([0xEF, 0xBB, 0xBF]));  # UTF-8 BOM
%!   fwrite (fid, "1,2\n3,4");
%!   fclose (fid);
%!
%!   assert (dlmread (file), [1, 2; 3, 4]);
%! unwind_protect_cleanup
%!   unlink (file);
%! end_unwind_protect
 
*/
 
OCTAVE_END_NAMESPACE(octave)