////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 1996-2022 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/>.
//
////////////////////////////////////////////////////////////////////////

#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif

#include <cassert>
#include <cctype>
#include <cstring>

#include <algorithm>
#include <deque>
#include <fstream>
#include <limits>
#include <iomanip>
#include <iostream>
#include <sstream>
#include <string>

#include "Array.h"
#include "Cell.h"
#include "byte-swap.h"
#include "lo-ieee.h"
#include "lo-mappers.h"
#include "lo-utils.h"
#include "oct-locbuf.h"
#include "octave-preserve-stream-state.h"
#include "quit.h"
#include "str-vec.h"
#include "strcase-wrappers.h"

#include "error.h"
#include "errwarn.h"
#include "input.h"
#include "interpreter-private.h"
#include "interpreter.h"
#include "octave.h"
#include "oct-iostrm.h"
#include "oct-stdstrm.h"
#include "oct-string.h"
#include "oct-stream.h"
#include "ov.h"
#include "ovl.h"
#include "pager.h"
#include "utils.h"

namespace octave
{
  // Programming Note: There are two very different error functions used
  // in the stream code.  When invoked with "error (...)" the member
  // function from stream or base_stream is called.  This
  // function sets the error state on the stream AND returns control to
  // the caller.  The caller must then return a value at the end of the
  // function.  When invoked with "::error (...)" the exception-based
  // error function from error.h is used.  This function will throw an
  // exception and not return control to the caller.  BE CAREFUL and
  // invoke the correct error function!

  // Possible values for conv_err:
  //
  //   1 : not a real scalar
  //   2 : value is NaN
  //   3 : value is not an integer

  static int
  convert_to_valid_int (const octave_value& tc, int& conv_err)
  {
    conv_err = 0;

    int retval = 0;

    double dval = 0.0;

    try
      {
        dval = tc.double_value ();
      }
    catch (const execution_exception&)
      {
        interpreter& interp = __get_interpreter__ ();

        interp.recover_from_exception ();

        conv_err = 1;
      }

    if (! conv_err)
      {
        if (! lo_ieee_isnan (dval))
          {
            int ival = math::nint (dval);

            if (ival == dval)
              retval = ival;
            else
              conv_err = 3;
          }
        else
          conv_err = 2;
      }

    return retval;
  }

  static octave_idx_type
  get_size (double d, const std::string& who)
  {
    octave_idx_type retval = -1;

    if (lo_ieee_isnan (d))
      ::error ("%s: NaN invalid as size specification", who.c_str ());

    if (math::isinf (d))
      retval = -1;
    else
      {
        if (d < 0.0)
          ::error ("%s: negative value invalid as size specification",
                   who.c_str ());

        static const double out_of_range_top
          = static_cast<double> (std::numeric_limits<octave_idx_type>::max ())
            + 1.;
        if (d >= out_of_range_top)
          ::error ("%s: dimension too large for Octave's index type",
                   who.c_str ());

        retval = math::nint_big (d);
      }

    return retval;
  }

  static void
  get_size (const Array<double>& size,
            octave_idx_type& nr, octave_idx_type& nc,
            bool& one_elt_size_spec, const std::string& who)
  {
    nr = -1;
    nc = -1;

    one_elt_size_spec = false;

    double dnr = -1.0;
    double dnc = -1.0;

    octave_idx_type sz_len = size.numel ();

    if (sz_len == 1)
      {
        one_elt_size_spec = true;

        dnr = size(0);

        dnc = (dnr == 0.0) ? 0.0 : 1.0;
      }
    else if (sz_len == 2)
      {
        dnr = size(0);

        if (math::isinf (dnr))
          ::error ("%s: infinite value invalid as size specification",
                   who.c_str ());

        dnc = size(1);
      }
    else
      ::error ("%s: invalid size specification (must be 2-D)", who.c_str ());

    nr = get_size (dnr, who);

    if (dnc >= 0.0)
      {
        nc = get_size (dnc, who);

        // Check for overflow.
        if (nr > 0 && nc > 0
            && nc > std::numeric_limits<octave_idx_type>::max () / nr)
          ::error ("%s: size too large for Octave's index type", who.c_str ());
      }
  }

  static std::string
  expand_char_class (const std::string& s)
  {
    std::string retval;

    std::size_t len = s.length ();

    std::size_t i = 0;

    while (i < len)
      {
        unsigned char c = s[i++];

        if (c == '-' && i > 1 && i < len
            && (   static_cast<unsigned char> (s[i-2])
                   <= static_cast<unsigned char> (s[i])))
          {
            // Add all characters from the range except the first (we
            // already added it below).

            for (c = s[i-2]+1; c < s[i]; c++)
              retval += c;
          }
        else
          {
            // Add the character to the class.  Only add '-' if it is
            // the last character in the class.

            if (c != '-' || i == len)
              retval += c;
          }
      }

    return retval;
  }

  class
  scanf_format_elt
  {
  public:

    enum special_conversion
    {
      whitespace_conversion = 1,
      literal_conversion = 2,
      null = 3
    };

    scanf_format_elt (const std::string& txt = "", int w = 0, bool d = false,
                      char typ = '\0', char mod = '\0',
                      const std::string& ch_class = "")
      : text (txt), width (w), discard (d), type (typ),
        modifier (mod), char_class (ch_class)
    { }

    scanf_format_elt (const scanf_format_elt&) = default;

    scanf_format_elt& operator = (const scanf_format_elt&) = default;

    ~scanf_format_elt (void) = default;

    // The C-style format string.
    std::string text;

    // The maximum field width.
    int width;

    // TRUE if we are not storing the result of this conversion.
    bool discard;

    // Type of conversion -- 'd', 'i', 'o', 'u', 'x', 'e', 'f', 'g',
    // 'c', 's', 'p', '%', or '['.
    char type;

    // A length modifier -- 'h', 'l', or 'L'.
    char modifier;

    // The class of characters in a '[' format.
    std::string char_class;
  };

  class
  scanf_format_list
  {
  public:

    scanf_format_list (const std::string& fmt = "");

    // No copying!

    scanf_format_list (const scanf_format_list&) = delete;

    scanf_format_list& operator = (const scanf_format_list&) = delete;

    ~scanf_format_list (void);

    octave_idx_type num_conversions (void) { return m_nconv; }

    // The length can be different than the number of conversions.
    // For example, "x %d y %d z" has 2 conversions but the length of
    // the list is 3 because of the characters that appear after the
    // last conversion.

    std::size_t length (void) const { return m_fmt_elts.size (); }

    const scanf_format_elt * first (void)
    {
      m_curr_idx = 0;
      return current ();
    }

    const scanf_format_elt * current (void) const
    {
      return length () > 0 ? m_fmt_elts[m_curr_idx] : nullptr;
    }

    const scanf_format_elt * next (bool cycle = true)
    {
      static scanf_format_elt dummy
        ("", 0, false, scanf_format_elt::null, '\0', "");

      m_curr_idx++;

      if (m_curr_idx >= length ())
        {
          if (cycle)
            m_curr_idx = 0;
          else
            return &dummy;
        }

      return current ();
    }

    void printme (void) const;

    bool ok (void) const { return (m_nconv >= 0); }

    operator bool () const { return ok (); }

    bool all_character_conversions (void);

    bool all_numeric_conversions (void);

  private:

    void add_elt_to_list (int width, bool discard, char type, char modifier,
                          const std::string& char_class = "");

    void process_conversion (const std::string& s, std::size_t& i,
                             std::size_t n, int& width, bool& discard,
                             char& type, char& modifier);

    int finish_conversion (const std::string& s, std::size_t& i, std::size_t n,
                           int width, bool discard, char& type,
                           char modifier);

    //--------

    // Number of conversions specified by this format string, or -1 if
    // invalid conversions have been found.
    octave_idx_type m_nconv;

    // Index to current element;
    std::size_t m_curr_idx;

    // List of format elements.
    std::deque<scanf_format_elt *> m_fmt_elts;

    // Temporary buffer.
    std::ostringstream m_buf;

  };

  scanf_format_list::scanf_format_list (const std::string& s)
    : m_nconv (0), m_curr_idx (0), m_fmt_elts (), m_buf ()
  {
    std::size_t n = s.length ();

    std::size_t i = 0;

    int width = 0;
    bool discard = false;
    char modifier = '\0';
    char type = '\0';

    bool have_more = true;

    while (i < n)
      {
        have_more = true;

        if (s[i] == '%')
          {
            // Process percent-escape conversion type.

            process_conversion (s, i, n, width, discard, type, modifier);

            have_more = (m_buf.tellp () != 0);
          }
        else if (isspace (s[i]))
          {
            type = scanf_format_elt::whitespace_conversion;

            width = 0;
            discard = false;
            modifier = '\0';
            m_buf << ' ';

            while (++i < n && isspace (s[i]))
              ; // skip whitespace

            add_elt_to_list (width, discard, type, modifier);

            have_more = false;
          }
        else
          {
            type = scanf_format_elt::literal_conversion;

            width = 0;
            discard = false;
            modifier = '\0';

            while (i < n && ! isspace (s[i]) && s[i] != '%')
              m_buf << s[i++];

            add_elt_to_list (width, discard, type, modifier);

            have_more = false;
          }

        if (m_nconv < 0)
          {
            have_more = false;
            break;
          }
      }

    if (have_more)
      add_elt_to_list (width, discard, type, modifier);

    m_buf.clear ();
    m_buf.str ("");
  }

  scanf_format_list::~scanf_format_list (void)
  {
    std::size_t n = m_fmt_elts.size ();

    for (std::size_t i = 0; i < n; i++)
      {
        scanf_format_elt *elt = m_fmt_elts[i];
        delete elt;
      }
  }

  void
  scanf_format_list::add_elt_to_list (int width, bool discard, char type,
                                      char modifier,
                                      const std::string& char_class)
  {
    std::string text = m_buf.str ();

    if (! text.empty ())
      {
        scanf_format_elt *elt
          = new scanf_format_elt (text, width, discard, type,
                                  modifier, char_class);

        m_fmt_elts.push_back (elt);
      }

    m_buf.clear ();
    m_buf.str ("");
  }

  void
  scanf_format_list::process_conversion (const std::string& s, std::size_t& i,
                                         std::size_t n, int& width,
                                         bool& discard, char& type,
                                         char& modifier)
  {
    width = 0;
    discard = false;
    modifier = '\0';
    type = '\0';

    m_buf << s[i++];

    bool have_width = false;

    while (i < n)
      {
        switch (s[i])
          {
          case '*':
            if (discard)
              m_nconv = -1;
            else
              {
                discard = true;
                m_buf << s[i++];
              }
            break;

          case '0': case '1': case '2': case '3': case '4':
          case '5': case '6': case '7': case '8': case '9':
            if (have_width)
              m_nconv = -1;
            else
              {
                char c = s[i++];
                width = 10 * width + c - '0';
                have_width = true;
                m_buf << c;
                while (i < n && isdigit (s[i]))
                  {
                    c = s[i++];
                    width = 10 * width + c - '0';
                    m_buf << c;
                  }
              }
            break;

          case 'h': case 'l': case 'L':
            if (modifier != '\0')
              m_nconv = -1;
            else
              modifier = s[i++];
            break;

          // We accept X for compatibility with undocumented Matlab behavior.
          case 'd': case 'i': case 'o': case 'u': case 'x':
          case 'X':
            if (modifier == 'L')
              {
                m_nconv = -1;
                break;
              }
            goto fini;

          // We accept E and G for compatibility with undocumented
          // Matlab behavior.
          case 'e': case 'f': case 'g':
          case 'E': case 'G':
            if (modifier == 'h')
              {
                m_nconv = -1;
                break;
              }

            // No float or long double conversions, thanks.
            m_buf << 'l';

            goto fini;

          case 'c': case 's': case 'p': case '%': case '[':
            if (modifier != '\0')
              {
                m_nconv = -1;
                break;
              }
            goto fini;

          fini:
            {
              if (finish_conversion (s, i, n, width, discard,
                                     type, modifier) == 0)
                return;
            }
            break;

          default:
            m_nconv = -1;
            break;
          }

        if (m_nconv < 0)
          break;
      }

    m_nconv = -1;
  }

  int
  scanf_format_list::finish_conversion (const std::string& s, std::size_t& i,
                                        std::size_t n, int width, bool discard,
                                        char& type, char modifier)
  {
    int retval = 0;

    std::string char_class;

    std::size_t beg_idx = std::string::npos;
    std::size_t end_idx = std::string::npos;

    if (s[i] == '%')
      {
        type = '%';
        m_buf << s[i++];
      }
    else
      {
        type = s[i];

        if (s[i] == '[')
          {
            m_buf << s[i++];

            if (i < n)
              {
                beg_idx = i;

                if (s[i] == '^')
                  {
                    type = '^';
                    m_buf << s[i++];

                    if (i < n)
                      {
                        beg_idx = i;

                        if (s[i] == ']')
                          m_buf << s[i++];
                      }
                  }
                else if (s[i] == ']')
                  m_buf << s[i++];
              }

            while (i < n && s[i] != ']')
              m_buf << s[i++];

            if (i < n && s[i] == ']')
              {
                end_idx = i-1;
                m_buf << s[i++];
              }

            if (s[i-1] != ']')
              retval = m_nconv = -1;
          }
        else
          m_buf << s[i++];

        m_nconv++;
      }

    if (m_nconv >= 0)
      {
        if (beg_idx != std::string::npos && end_idx != std::string::npos)
          char_class = expand_char_class (s.substr (beg_idx,
                                                    end_idx - beg_idx + 1));

        add_elt_to_list (width, discard, type, modifier, char_class);
      }

    return retval;
  }

  void
  scanf_format_list::printme (void) const
  {
    std::size_t n = m_fmt_elts.size ();

    for (std::size_t i = 0; i < n; i++)
      {
        scanf_format_elt *elt = m_fmt_elts[i];

        std::cerr
          << "width:      " << elt->width << "\n"
          << "discard:    " << elt->discard << "\n"
          << "type:       ";

        if (elt->type == scanf_format_elt::literal_conversion)
          std::cerr << "literal text\n";
        else if (elt->type == scanf_format_elt::whitespace_conversion)
          std::cerr << "whitespace\n";
        else
          std::cerr << elt->type << "\n";

        std::cerr
          << "modifier:   " << elt->modifier << "\n"
          << "char_class: '" << undo_string_escapes (elt->char_class) << "'\n"
          << "text:       '" << undo_string_escapes (elt->text) << "'\n\n";
      }
  }

  bool
  scanf_format_list::all_character_conversions (void)
  {
    std::size_t n = m_fmt_elts.size ();

    if (n > 0)
      {
        for (std::size_t i = 0; i < n; i++)
          {
            scanf_format_elt *elt = m_fmt_elts[i];

            switch (elt->type)
              {
              case 'c': case 's': case '%': case '[': case '^':
              case scanf_format_elt::literal_conversion:
              case scanf_format_elt::whitespace_conversion:
                break;

              default:
                return false;
                break;
              }
          }

        return true;
      }
    else
      return false;
  }

  bool
  scanf_format_list::all_numeric_conversions (void)
  {
    std::size_t n = m_fmt_elts.size ();

    if (n > 0)
      {
        for (std::size_t i = 0; i < n; i++)
          {
            scanf_format_elt *elt = m_fmt_elts[i];

            switch (elt->type)
              {
              case 'd': case 'i': case 'o': case 'u': case 'x': case 'X':
              case 'e': case 'f': case 'g': case 'E': case 'G':
                break;

              default:
                return false;
                break;
              }
          }

        return true;
      }
    else
      return false;
  }

  class
  printf_format_elt
  {
  public:

    printf_format_elt (const std::string& txt = "", int n = 0, int w = -1,
                       int p = -1, const std::string& f = "",
                       char typ = '\0', char mod = '\0')
      : text (txt), args (n), fw (w), prec (p), flags (f),
        type (typ), modifier (mod)
    { }

    printf_format_elt (const printf_format_elt&) = default;

    printf_format_elt& operator = (const printf_format_elt&) = default;

    ~printf_format_elt (void) = default;

    // The C-style format string.
    std::string text;

    // How many args do we expect to consume?
    int args;

    // Field width.
    int fw;

    // Precision.
    int prec;

    // Flags -- '-', '+', ' ', '0', or '#'.
    std::string flags;

    // Type of conversion -- 'd', 'i', 'o', 'x', 'X', 'u', 'c', 's',
    // 'f', 'e', 'E', 'g', 'G', 'p', or '%'
    char type;

    // A length modifier -- 'h', 'l', or 'L'.
    char modifier;
  };

  class
  printf_format_list
  {
  public:

    printf_format_list (const std::string& fmt = "");

    // No copying!

    printf_format_list (const printf_format_list&) = delete;

    printf_format_list& operator = (const printf_format_list&) = delete;

    ~printf_format_list (void);

    octave_idx_type num_conversions (void) { return m_nconv; }

    const printf_format_elt * first (void)
    {
      m_curr_idx = 0;
      return current ();
    }

    const printf_format_elt * current (void) const
    {
      return length () > 0 ? m_fmt_elts[m_curr_idx] : nullptr;
    }

    std::size_t length (void) const { return m_fmt_elts.size (); }

    const printf_format_elt * next (bool cycle = true)
    {
      m_curr_idx++;

      if (m_curr_idx >= length ())
        {
          if (cycle)
            m_curr_idx = 0;
          else
            return nullptr;
        }

      return current ();
    }

    bool last_elt_p (void) { return (m_curr_idx + 1 == length ()); }

    void printme (void) const;

    bool ok (void) const { return (m_nconv >= 0); }

    operator bool () const { return ok (); }

  private:

    void add_elt_to_list (int args, const std::string& flags, int fw,
                          int prec, char type, char modifier);

    void process_conversion (const std::string& s, std::size_t& i,
                             std::size_t n,
                             int& args, std::string& flags, int& fw,
                             int& prec, char& modifier, char& type);

    void finish_conversion (const std::string& s, std::size_t& i, int args,
                            const std::string& flags, int fw, int prec,
                            char modifier, char& type);

    //--------

    // Number of conversions specified by this format string, or -1 if
    // invalid conversions have been found.
    octave_idx_type m_nconv;

    // Index to current element;
    std::size_t m_curr_idx;

    // List of format elements.
    std::deque<printf_format_elt *> m_fmt_elts;

    // Temporary buffer.
    std::ostringstream m_buf;

  };

  printf_format_list::printf_format_list (const std::string& s)
    : m_nconv (0), m_curr_idx (0), m_fmt_elts (), m_buf ()
  {
    std::size_t n = s.length ();

    std::size_t i = 0;

    int args = 0;
    std::string flags;
    int fw = -1;
    int prec = -1;
    char modifier = '\0';
    char type = '\0';

    bool have_more = true;
    bool empty_buf = true;

    if (n == 0)
      {
        printf_format_elt *elt
          = new printf_format_elt ("", args, fw, prec, flags, type, modifier);

        m_fmt_elts.push_back (elt);
      }
    else
      {
        while (i < n)
          {
            have_more = true;

            empty_buf = (m_buf.tellp () == 0);

            switch (s[i])
              {
              case '%':
                {
                  if (empty_buf)
                    {
                      process_conversion (s, i, n, args, flags, fw, prec,
                                          modifier, type);

                      // If there is nothing in the buffer, then
                      // add_elt_to_list must have just been called, so we
                      // are already done with the current element and we
                      // don't need to call add_elt_to_list if this is our
                      // last trip through the loop.

                      have_more = (m_buf.tellp () != 0);
                    }
                  else
                    add_elt_to_list (args, flags, fw, prec, type, modifier);
                }
                break;

              default:
                {
                  args = 0;
                  flags = "";
                  fw = -1;
                  prec = -1;
                  modifier = '\0';
                  type = '\0';
                  m_buf << s[i++];
                }
                break;
              }

            if (m_nconv < 0)
              {
                have_more = false;
                break;
              }
          }

        if (have_more)
          add_elt_to_list (args, flags, fw, prec, type, modifier);

        m_buf.clear ();
        m_buf.str ("");
      }
  }

  printf_format_list::~printf_format_list (void)
  {
    std::size_t n = m_fmt_elts.size ();

    for (std::size_t i = 0; i < n; i++)
      {
        printf_format_elt *elt = m_fmt_elts[i];
        delete elt;
      }
  }

  void
  printf_format_list::add_elt_to_list (int args, const std::string& flags,
                                       int fw, int prec, char type,
                                       char modifier)
  {
    std::string text = m_buf.str ();

    if (! text.empty ())
      {
        printf_format_elt *elt
          = new printf_format_elt (text, args, fw, prec, flags,
                                   type, modifier);

        m_fmt_elts.push_back (elt);
      }

    m_buf.clear ();
    m_buf.str ("");
  }

  void
  printf_format_list::process_conversion (const std::string& s, std::size_t& i,
                                          std::size_t n, int& args,
                                          std::string& flags, int& fw,
                                          int& prec, char& modifier,
                                          char& type)
  {
    args = 0;
    flags = "";
    fw = -1;
    prec = -1;
    modifier = '\0';
    type = '\0';

    m_buf << s[i++];

    bool nxt = false;

    while (i < n)
      {
        switch (s[i])
          {
          case '-': case '+': case ' ': case '0': case '#':
            flags += s[i];
            m_buf << s[i++];
            break;

          default:
            nxt = true;
            break;
          }

        if (nxt)
          break;
      }

    if (i < n)
      {
        if (s[i] == '*')
          {
            fw = -2;
            args++;
            m_buf << s[i++];
          }
        else
          {
            if (isdigit (s[i]))
              {
                int nn = 0;
                std::string tmp = s.substr (i);
                sscanf (tmp.c_str (), "%d%n", &fw, &nn);
              }

            while (i < n && isdigit (s[i]))
              m_buf << s[i++];
          }
      }

    if (i < n && s[i] == '.')
      {
        // nothing before the . means 0.
        if (fw == -1)
          fw = 0;

        // . followed by nothing is 0.
        prec = 0;

        m_buf << s[i++];

        if (i < n)
          {
            if (s[i] == '*')
              {
                prec = -2;
                args++;
                m_buf << s[i++];
              }
            else
              {
                if (isdigit (s[i]))
                  {
                    int nn = 0;
                    std::string tmp = s.substr (i);
                    sscanf (tmp.c_str (), "%d%n", &prec, &nn);
                  }

                while (i < n && isdigit (s[i]))
                  m_buf << s[i++];
              }
          }
      }

    if (i < n)
      {
        // Accept and record modifier, but don't place it in the format
        // item text.  All integer conversions are handled as 64-bit
        // integers.

        switch (s[i])
          {
          case 'h': case 'l': case 'L':
            modifier = s[i++];
            break;

          default:
            break;
          }
      }

    if (i < n)
      finish_conversion (s, i, args, flags, fw, prec, modifier, type);
    else
      m_nconv = -1;
  }

  void
  printf_format_list::finish_conversion (const std::string& s, std::size_t& i,
                                         int args, const std::string& flags,
                                         int fw, int prec, char modifier,
                                         char& type)
  {
    switch (s[i])
      {
      case 'd': case 'i': case 'o': case 'x': case 'X':
      case 'u': case 'c':
        if (modifier == 'L')
          {
            m_nconv = -1;
            break;
          }
        goto fini;

      case 'f': case 'e': case 'E': case 'g': case 'G':
        if (modifier == 'h' || modifier == 'l')
          {
            m_nconv = -1;
            break;
          }
        goto fini;

      case 's': case 'p': case '%':
        if (modifier != '\0')
          {
            m_nconv = -1;
            break;
          }
        goto fini;

      fini:

        type = s[i];

        m_buf << s[i++];

        if (type != '%' || args != 0)
          m_nconv++;

        if (type != '%')
          args++;

        add_elt_to_list (args, flags, fw, prec, type, modifier);

        break;

      default:
        m_nconv = -1;
        break;
      }
  }

  void
  printf_format_list::printme (void) const
  {
    std::size_t n = m_fmt_elts.size ();

    for (std::size_t i = 0; i < n; i++)
      {
        printf_format_elt *elt = m_fmt_elts[i];

        std::cerr
          << "args:     " << elt->args << "\n"
          << "flags:    '" << elt->flags << "'\n"
          << "width:    " << elt->fw << "\n"
          << "prec:     " << elt->prec << "\n"
          << "type:     '" << elt->type << "'\n"
          << "modifier: '" << elt->modifier << "'\n"
          << "text:     '" << undo_string_escapes (elt->text) << "'\n\n";
      }
  }

  // Calculate x^n.  Used for ...e+nn so that, for example, 1e2 is
  // exactly 100 and 5e-1 is 1/2

  static double
  pown (double x, unsigned int n)
  {
    double retval = 1;

    for (unsigned int d = n; d; d >>= 1)
      {
        if (d & 1)
          retval *= x;
        x *= x;
      }

    return retval;
  }

  static Cell
  init_inf_nan (void)
  {
    Cell retval (dim_vector (1, 2));

    retval(0) = Cell (octave_value ("inf"));
    retval(1) = Cell (octave_value ("nan"));

    return retval;
  }

  // Delimited stream, optimized to read strings of characters separated
  // by single-character delimiters.
  //
  // The reason behind this class is that octstream doesn't provide
  // seek/tell, but the opportunity has been taken to optimise for the
  // textscan workload.
  //
  // The function reads chunks into a 4kiB buffer, and marks where the
  // last delimiter occurs.  Reads up to this delimiter can be fast.
  // After that last delimiter, the remaining text is moved to the front
  // of the buffer and the buffer is refilled.  This also allows cheap
  // seek and tell operations within a "fast read" block.

  class
  delimited_stream
  {
  public:

    delimited_stream (std::istream& is, const std::string& delimiters,
                      int longest_lookahead, octave_idx_type bsize = 4096);

    delimited_stream (std::istream& is, const delimited_stream& ds);

    // No copying!

    delimited_stream (const delimited_stream&) = delete;

    delimited_stream& operator = (const delimited_stream&) = delete;

    ~delimited_stream (void);

    // Called when optimized sequence of get is finished.  Ensures that
    // there is a remaining delimiter in buf, or loads more data in.
    void field_done (void)
    {
      if (m_idx >= m_last)
        refresh_buf ();
    }

    // Load new data into buffer, and set eob, last, idx.
    // Return EOF at end of file, 0 otherwise.
    int refresh_buf (bool initialize = false);

    // Get a character, relying on caller to call field_done if
    // a delimiter has been reached.
    int get (void)
    {
      if (m_delimited)
        return eof () ? std::istream::traits_type::eof () : *m_idx++;
      else
        return get_undelim ();
    }

    // Get a character, checking for underrun of the buffer.
    int get_undelim (void);

    // Read character that will be got by the next get.
    // FIXME: This will not set EOF if delimited stream is at EOF and a peek
    // is attempted.  This does *NOT* behave like C++ input stream.
    // For a compatible peek function, use peek_undelim.  See bug #56917.
    int peek (void)
    { return eof () ? std::istream::traits_type::eof () : *m_idx; }

    // Read character that will be got by the next get.
    int peek_undelim (void);

    // Undo a 'get' or 'get_undelim'.  It is the caller's responsibility
    // to avoid overflow by calling putbacks only for a character got by
    // get() or get_undelim(), with no intervening
    // get, get_delim, field_done, refresh_buf, getline, read or seekg.
    void putback (char /*ch*/ = 0) { if (! eof ()) --m_idx; }

    int getline  (std::string& dest, char delim);

    // int skipline (char delim);

    char * read (char *buffer, int size, char* &new_start);

    // Return a position suitable to "seekg", valid only within this
    // block between calls to field_done.
    char * tellg (void) { return m_idx; }

    void seekg (char *old_idx) { m_idx = old_idx; }

    bool eof (void)
    {
      return (m_eob == m_buf + m_overlap && m_i_stream.eof ())
              || (m_flags & std::ios_base::eofbit);
    }

    operator const void* (void)
    { return (! eof () && ! m_flags) ? this : nullptr; }

    bool fail (void) { return m_flags & std::ios_base::failbit; }

    std::ios_base::iostate rdstate (void) { return m_flags; }

    void setstate (std::ios_base::iostate m) { m_flags = m_flags | m; }

    void clear (std::ios_base::iostate m
                = (std::ios_base::eofbit & ~std::ios_base::eofbit))
    {
      m_flags = m_flags & m;
    }

    // Report if any characters have been consumed.
    // (get, read, etc. not cancelled by putback or seekg)

    void progress_benchmark (void) { m_progress_marker = m_idx; }

    bool no_progress (void) { return m_progress_marker == m_idx; }

    // Number of characters remaining until end of stream if it is already
    // buffered. int_max otherwise.

    std::ptrdiff_t remaining (void)
    {
      if (m_eob < m_buf + m_bufsize)
        return m_eob - m_idx;
      else
        return std::numeric_limits<std::ptrdiff_t>::max ();
    }

  private:

    // Number of characters to read from the file at once.
    int m_bufsize;

    // Stream to read from.
    std::istream& m_i_stream;

    // Temporary storage for a "chunk" of data.
    char *m_buf;

    // Current read pointer.
    char *m_idx;

    // Location of last delimiter in the buffer at buf (undefined if
    // delimited is false).
    char *m_last;

    // Position after last character in buffer.
    char *m_eob;

    // Overlap with old content when refreshing buffer.
    std::ptrdiff_t m_overlap;

    // True if there is delimiter in the buffer after idx.
    bool m_delimited;

    // Longest lookahead required.
    int m_longest;

    // Sequence of single-character delimiters.
    const std::string m_delims;

    // Position of start of buf in original stream.
    std::streampos m_buf_in_file;

    // Marker to see if a read consumes any characters.
    char *m_progress_marker;

    std::ios_base::iostate m_flags;
  };

  // Create a delimited stream, reading from is, with delimiters delims,
  // and allowing reading of up to tellg + longest_lookeahead.  When is
  // is at EOF, lookahead may be padded by ASCII nuls.

  delimited_stream::delimited_stream (std::istream& is,
                                      const std::string& delimiters,
                                      int longest_lookahead,
                                      octave_idx_type bsize)
    : m_bufsize (bsize), m_i_stream (is), m_longest (longest_lookahead),
      m_delims (delimiters),
      m_flags (std::ios::failbit & ~std::ios::failbit) // can't cast 0
  {
    m_buf = new char[m_bufsize];
    m_eob = m_buf + m_bufsize;
    m_idx = m_eob;                // refresh_buf shouldn't try to copy old data
    m_progress_marker = m_idx;
    refresh_buf (true);           // load the first batch of data
  }

  // Used to create a stream from a strstream from data read from a dstr.
  delimited_stream::delimited_stream (std::istream& is,
                                      const delimited_stream& ds)
    : delimited_stream (is, ds.m_delims, ds.m_longest, ds.m_bufsize)
  { }

  delimited_stream::~delimited_stream (void)
  {
    // Seek to the correct position in i_stream.
    if (! eof ())
      {
        m_i_stream.clear ();
        m_i_stream.seekg (m_buf_in_file);
        m_i_stream.read (m_buf, m_idx - m_buf - m_overlap);
      }

    delete [] m_buf;
  }

  // Read a character from the buffer, refilling the buffer from the file
  // if necessary.

  int
  delimited_stream::get_undelim (void)
  {
    int retval;
    if (eof ())
      {
        setstate (std::ios_base::failbit);
        return std::istream::traits_type::eof ();
      }

    if (m_idx < m_eob)
      retval = *m_idx++;
    else
      {
        refresh_buf ();

        if (eof ())
          {
            setstate (std::ios_base::eofbit);
            retval = std::istream::traits_type::eof ();
          }
        else
          retval = *m_idx++;
      }

    if (m_idx >= m_last)
      m_delimited = false;

    return retval;
  }

  // Return the next character to be read without incrementing the
  // pointer, refilling the buffer from the file if necessary.

  int
  delimited_stream::peek_undelim (void)
  {
    int retval = get_undelim ();
    putback ();

    return retval;
  }

  // Copy remaining unprocessed data to the start of the buffer and load
  // new data to fill it.  Return EOF if the file is at EOF before
  // reading any data and all of the data that has been read has been
  // processed.

  int
  delimited_stream::refresh_buf (bool initialize)
  {
    if (eof ())
      return std::istream::traits_type::eof ();

    int retval;

    if (m_eob < m_idx)
      m_idx = m_eob;

    std::size_t old_remaining = m_eob - m_idx;
    std::size_t old_overlap = 0;

    if (initialize || (m_idx - m_buf <= 0))
      m_overlap = 0;
    else
      {
        old_overlap = m_overlap;
        // Retain the last 25 bytes in the buffer.  That should be more than enough
        // to putback an entire double precision floating point number in decimal
        // including 3 digit exponent and signs.  Do we ever need to putback more
        // than that?
        m_overlap = 25;
        // Assure we don't "underflow" with the overlap
        m_overlap = std::min (m_overlap, m_idx - m_buf - 1);
      }

    octave_quit ();                       // allow ctrl-C

    if (old_remaining + m_overlap > 0)
      {
        m_buf_in_file += (m_idx - old_overlap - m_buf);
        std::memmove (m_buf, m_idx - m_overlap, m_overlap + old_remaining);
      }
    else
      m_buf_in_file = m_i_stream.tellg ();  // record for destructor

    // where original idx would have been
    m_progress_marker -= m_idx - m_overlap - m_buf;
    m_idx = m_buf + m_overlap;

    int gcount;   // chars read
    if (! m_i_stream.eof ())
      {
        m_i_stream.read (m_buf + m_overlap + old_remaining,
                         m_bufsize - m_overlap - old_remaining);
        gcount = m_i_stream.gcount ();
      }
    else
      gcount = 0;

    m_eob = m_buf + m_overlap + old_remaining + gcount;
    m_last = m_eob;
    if (gcount == 0)
      {
        m_delimited = false;

        if (m_eob != m_buf + m_overlap)
          // no more data in file, but still some to go
          retval = 0;
        else
          // file and buffer are both done.
          retval = std::istream::traits_type::eof ();
      }
    else
      {
        m_delimited = true;

        for (m_last = m_eob - m_longest; m_last - m_buf - m_overlap >= 0;
             m_last--)
          {
            if (m_delims.find (*m_last) != std::string::npos)
              break;
          }

        if (m_last < m_buf + m_overlap)
          m_delimited = false;

        retval = 0;
      }

    // Ensure fast peek doesn't give valid char
    if (retval == std::istream::traits_type::eof ())
      *m_idx = '\0';    // FIXME: check that no TreatAsEmpty etc starts w. \0?

    return retval;
  }

  // Return a pointer to a block of data of size size, assuming that a
  // sufficiently large buffer is available in buffer, if required.
  // If called when delimited == true, and size is no greater than
  // longest_lookahead then this will not call refresh_buf, so seekg
  // still works.  Otherwise, seekg may be invalidated.

  char *
  delimited_stream::read (char *buffer, int size, char* &prior_tell)
  {
    char *retval;

    if (m_eob - m_idx >= size)
      {
        retval = m_idx;
        m_idx += size;
        if (m_idx > m_last)
          m_delimited = false;
      }
    else
      {
        // If there was a tellg pointing to an earlier point than the current
        // read position, try to keep it in the active buffer.
        // In the current code, prior_tell==idx for each call,
        // so this is not necessary, just a precaution.

        if (m_eob - prior_tell + size < m_bufsize)
          {
            octave_idx_type gap = m_idx - prior_tell;
            m_idx = prior_tell;
            refresh_buf ();
            m_idx += gap;
          }
        else      // can't keep the tellg in range.  May skip some data.
          {
            refresh_buf ();
          }

        prior_tell = m_buf;

        if (m_eob - m_idx > size)
          {
            retval = m_idx;
            m_idx += size;
            if (m_idx > m_last)
              m_delimited = false;
          }
        else
          {
            if (size <= m_bufsize)          // small read, but reached EOF
              {
                retval = m_idx;
                memset (m_eob, 0, size + (m_idx - m_buf));
                m_idx += size;
              }
            else  // Reading more than the whole buf; return it in buffer
              {
                retval = buffer;
                // FIXME: read bufsize at a time
                int i;
                for (i = 0; i < size && ! eof (); i++)
                  *buffer++ = get_undelim ();
                if (eof ())
                  memset (buffer, 0, size - i);
              }
          }
      }

    return retval;
  }

  // Return in OUT an entire line, terminated by delim.  On input, OUT
  // must have length at least 1.

  int
  delimited_stream::getline (std::string& out, char delim)
  {
    int len = out.length ();
    int used = 0;
    int ch;
    while ((ch = get_undelim ()) != delim
           && ch != std::istream::traits_type::eof ())
      {
        out[used++] = ch;
        if (used == len)
          {
            len <<= 1;
            out.resize (len);
          }
      }
    out.resize (used);
    field_done ();

    return ch;
  }

  // A single conversion specifier, such as %f or %c.

  class
  textscan_format_elt
  {
  public:

    enum special_conversion
    {
      whitespace_conversion = 1,
      literal_conversion = 2
    };

    textscan_format_elt (const std::string& txt, int w = 0, int p = -1,
                         int bw = 0, bool dis = false, char typ = '\0',
                         const std::string& ch_class = std::string ())
      : text (txt), width (w), prec (p), bitwidth (bw),
        char_class (ch_class), type (typ), discard (dis),
        numeric (typ == 'd' || typ == 'u' || type == 'f' || type == 'n')
    { }

    textscan_format_elt (const textscan_format_elt& e)
      : text (e.text), width (e.width), prec (e.prec),
        bitwidth (e.bitwidth), char_class (e.char_class), type (e.type),
        discard (e.discard), numeric (e.numeric)
    { }

    textscan_format_elt& operator = (const textscan_format_elt& e)
    {
      if (this != &e)
        {
          text = e.text;
          width = e.width;
          prec = e.prec;
          bitwidth = e.bitwidth;
          discard = e.discard;
          type = e.type;
          numeric = e.numeric;
          char_class = e.char_class;
        }

      return *this;
    }

    // The C-style format string.
    std::string text;

    // The maximum field width.
    unsigned int width;

    // The maximum number of digits to read after the decimal in a
    // floating point conversion.
    int prec;

    // The size of the result.  For integers, bitwidth may be 8, 16, 34,
    // or 64.  For floating point values, bitwidth may be 32 or 64.
    int bitwidth;

    // The class of characters in a '[' or '^' format.
    std::string char_class;

    // Type of conversion
    //  -- 'd', 'u', 'f', 'n', 's', 'q', 'c', '%', 'C', 'D', '[' or '^'.
    char type;

    // TRUE if we are not storing the result of this conversion.
    bool discard;

    // TRUE if the type is 'd', 'u', 'f', 'n'
    bool numeric;
  };

  // The (parsed) sequence of format specifiers.

  class textscan;

  class
  textscan_format_list
  {
  public:

    textscan_format_list (const std::string& fmt = std::string (),
                          const std::string& who = "textscan");
    // No copying!

    textscan_format_list (const textscan_format_list&) = delete;

    textscan_format_list& operator = (const textscan_format_list&) = delete;

    ~textscan_format_list (void);

    octave_idx_type num_conversions (void) const { return m_nconv; }

    // The length can be different than the number of conversions.
    // For example, "x %d y %d z" has 2 conversions but the length of
    // the list is 3 because of the characters that appear after the
    // last conversion.

    std::size_t numel (void) const { return m_fmt_elts.size (); }

    const textscan_format_elt * first (void)
    {
      m_curr_idx = 0;
      return current ();
    }

    const textscan_format_elt * current (void) const
    {
      return numel () > 0 ? m_fmt_elts[m_curr_idx] : nullptr;
    }

    const textscan_format_elt * next (bool cycle = true)
    {
      m_curr_idx++;

      if (m_curr_idx >= numel ())
        {
          if (cycle)
            m_curr_idx = 0;
          else
            return nullptr;
        }

      return current ();
    }

    void printme (void) const;

    bool ok (void) const { return (m_nconv >= 0); }

    operator const void* (void) const { return ok () ? this : nullptr; }

    // What function name should be shown when reporting errors.
    std::string who;

    // True if number of %f to be set from data file.
    bool set_from_first;

    // At least one conversion specifier is s,q,c, or [...].
    bool has_string;

    int read_first_row (delimited_stream& is, textscan& ts);

    std::list<octave_value> out_buf (void) const
    { return (m_output_container); }

  private:

    void add_elt_to_list (unsigned int width, int prec, int bitwidth,
                          octave_value val_type, bool discard,
                          char type,
                          const std::string& char_class = std::string ());

    void process_conversion (const std::string& s, std::size_t& i,
                             std::size_t n);

    std::string parse_char_class (const std::string& pattern) const;

    int finish_conversion (const std::string& s, std::size_t& i, std::size_t n,
                           unsigned int width, int prec, int bitwidth,
                           octave_value& val_type,
                           bool discard, char& type);

    //--------

    // Number of conversions specified by this format string, or -1 if
    // invalid conversions have been found.
    octave_idx_type m_nconv;

    // Index to current element;
    std::size_t m_curr_idx;

    // List of format elements.
    std::deque<textscan_format_elt *> m_fmt_elts;

    // list holding column arrays of types specified by conversions
    std::list<octave_value> m_output_container;

    // Temporary buffer.
    std::ostringstream m_buf;

  };

  // Main class to implement textscan.  Read data and parse it
  // according to a format.
  //
  // The calling sequence is
  //
  //   textscan scanner ();
  //   scanner.scan (...);

  class
  OCTINTERP_API
  textscan
  {
  public:

    textscan (const std::string& who_arg = "textscan",
              const std::string& encoding = "utf-8");

    // No copying!

    textscan (const textscan&) = delete;

    textscan& operator = (const textscan&) = delete;

    ~textscan (void) = default;

    octave_value scan (std::istream& isp, const std::string& fmt,
                       octave_idx_type ntimes,
                       const octave_value_list& options,
                       octave_idx_type& read_count);

  private:

    friend class textscan_format_list;

    octave_value do_scan (std::istream& isp, textscan_format_list& fmt_list,
                          octave_idx_type ntimes);

    void parse_options (const octave_value_list& args,
                        textscan_format_list& fmt_list);

    int read_format_once (delimited_stream& isp, textscan_format_list& fmt_list,
                          std::list<octave_value>& retval,
                          Array<octave_idx_type> row, int& done_after);

    void scan_one (delimited_stream& is, const textscan_format_elt& fmt,
                   octave_value& ov, Array<octave_idx_type> row);

    // Methods to process a particular conversion specifier.
    double read_double (delimited_stream& is,
                        const textscan_format_elt& fmt) const;

    void scan_complex (delimited_stream& is, const textscan_format_elt& fmt,
                       Complex& val) const;

    int scan_bracket (delimited_stream& is, const std::string& pattern,
                      std::string& val) const;

    int scan_caret (delimited_stream& is, const std::string& pattern,
                    std::string& val) const;

    void scan_string (delimited_stream& is, const textscan_format_elt& fmt,
                      std::string& val) const;

    void scan_cstring (delimited_stream& is, const textscan_format_elt& fmt,
                       std::string& val) const;

    void scan_qstring (delimited_stream& is, const textscan_format_elt& fmt,
                       std::string& val);

    // Helper methods.
    std::string read_until (delimited_stream& is, const Cell& delimiters,
                            const std::string& ends) const;

    int lookahead (delimited_stream& is, const Cell& targets, int max_len,
                   bool case_sensitive = true) const;

    bool match_literal (delimited_stream& isp, const textscan_format_elt& elem);

    int skip_whitespace (delimited_stream& is, bool EOLstop = true);

    int skip_delim (delimited_stream& is);

    bool is_delim (unsigned char ch) const
    {
      return ((m_delim_table.empty ()
               && (isspace (ch) || ch == m_eol1 || ch == m_eol2))
              || m_delim_table[ch] != '\0');
    }

    bool isspace (unsigned int ch) const
    { return m_whitespace_table[ch & 0xff]; }

    // True if the only delimiter is whitespace.
    bool whitespace_delim (void) const { return m_delim_table.empty (); }

    //--------

    // What function name should be shown when reporting errors.
    std::string m_who;

    std::string m_encoding;

    std::string m_buf;

    // Three cases for delim_table and delim_list
    // 1. delim_table empty, delim_list empty:  whitespace delimiters
    // 2. delim_table = look-up table of delim chars, delim_list empty.
    // 3. delim_table non-empty, delim_list = Cell array of delim strings

    std::string m_whitespace_table;

    // delim_table[i] == '\0' if i is not a delimiter.
    std::string m_delim_table;

    // String of delimiter characters.
    std::string m_delims;

    Cell m_comment_style;

    // How far ahead to look to detect an open comment.
    int m_comment_len;

    // First character of open comment.
    int m_comment_char;

    octave_idx_type m_buffer_size;

    std::string m_date_locale;

    // 'inf' and 'nan' for formatted_double.
    Cell m_inf_nan;

    // Array of strings of delimiters.
    Cell m_delim_list;

    // Longest delimiter.
    int m_delim_len;

    octave_value m_empty_value;
    std::string m_exp_chars;
    int m_header_lines;
    Cell m_treat_as_empty;

    // Longest string to treat as "N/A".
    int m_treat_as_empty_len;

    std::string m_whitespace;

    short m_eol1;
    short m_eol2;
    short m_return_on_error;

    bool m_collect_output;
    bool multiple_delims_as_one;
    bool m_default_exp;

    octave_idx_type m_lines;
  };

  textscan_format_list::textscan_format_list (const std::string& s,
                                              const std::string& who_arg)
    : who (who_arg), set_from_first (false), has_string (false),
      m_nconv (0), m_curr_idx (0), m_fmt_elts (), m_buf ()
  {
    std::size_t n = s.length ();

    std::size_t i = 0;

    unsigned int width = -1;    // Unspecified width = max (except %c)
    int prec = -1;
    int bitwidth = 0;
    bool discard = false;
    char type = '\0';

    bool have_more = true;

    if (s.empty ())
      {
        m_buf.clear ();
        m_buf.str ("");

        m_buf << "%f";

        bitwidth = 64;
        type = 'f';
        add_elt_to_list (width, prec, bitwidth, octave_value (NDArray ()),
                         discard, type);
        have_more = false;
        set_from_first = true;
        m_nconv = 1;
      }
    else
      {
        set_from_first = false;

        while (i < n)
          {
            have_more = true;

            if (s[i] == '%' && (i+1 == n || s[i+1] != '%'))
              {
                // Process percent-escape conversion type.

                process_conversion (s, i, n);

                // If there is nothing in the buffer, then add_elt_to_list
                // must have just been called, so we are already done with
                // the current element and we don't need to call
                // add_elt_to_list if this is our last trip through the
                // loop.

                have_more = (m_buf.tellp () != 0);
              }
            else if (isspace (s[i]))
              {
                while (++i < n && isspace (s[i]))
                  /* skip whitespace */;

                have_more = false;
              }
            else
              {
                type = textscan_format_elt::literal_conversion;

                width = 0;
                prec = -1;
                bitwidth = 0;
                discard = true;

                while (i < n && ! isspace (s[i])
                       && (s[i] != '%' || (i+1 < n && s[i+1] == '%')))
                  {
                    if (s[i] == '%')      // if double %, skip one
                      i++;
                    m_buf << s[i++];
                    width++;
                  }

                add_elt_to_list (width, prec, bitwidth, octave_value (),
                                 discard, type);

                have_more = false;
              }

            if (m_nconv < 0)
              {
                have_more = false;
                break;
              }
          }
      }

    if (have_more)
      add_elt_to_list (width, prec, bitwidth, octave_value (), discard, type);

    m_buf.clear ();
    m_buf.str ("");
  }

  textscan_format_list::~textscan_format_list (void)
  {
    std::size_t n = numel ();

    for (std::size_t i = 0; i < n; i++)
      {
        textscan_format_elt *elt = m_fmt_elts[i];
        delete elt;
      }
  }

  void
  textscan_format_list::add_elt_to_list (unsigned int width, int prec,
                                         int bitwidth, octave_value val_type,
                                         bool discard, char type,
                                         const std::string& char_class)
  {
    std::string text = m_buf.str ();

    if (! text.empty ())
      {
        textscan_format_elt *elt
          = new textscan_format_elt (text, width, prec, bitwidth, discard,
                                     type, char_class);

        if (! discard)
          m_output_container.push_back (val_type);

        m_fmt_elts.push_back (elt);
      }

    m_buf.clear ();
    m_buf.str ("");
  }

  void
  textscan_format_list::process_conversion (const std::string& s,
                                            std::size_t& i, std::size_t n)
  {
    unsigned width = 0;
    int prec = -1;
    int bitwidth = 0;
    bool discard = false;
    octave_value val_type;
    char type = '\0';

    m_buf << s[i++];

    bool have_width = false;

    while (i < n)
      {
        switch (s[i])
          {
          case '*':
            if (discard)
              m_nconv = -1;
            else
              {
                discard = true;
                m_buf << s[i++];
              }
            break;

          case '0': case '1': case '2': case '3': case '4':
          case '5': case '6': case '7': case '8': case '9':
            if (have_width)
              m_nconv = -1;
            else
              {
                char c = s[i++];
                width = width * 10 + c - '0';
                have_width = true;
                m_buf << c;
                while (i < n && isdigit (s[i]))
                  {
                    c = s[i++];
                    width = width * 10 + c - '0';
                    m_buf << c;
                  }

                if (i < n && s[i] == '.')
                  {
                    m_buf << s[i++];
                    prec = 0;
                    while (i < n && isdigit (s[i]))
                      {
                        c = s[i++];
                        prec = prec * 10 + c - '0';
                        m_buf << c;
                      }
                  }
              }
            break;

          case 'd': case 'u':
            {
              bool done = true;
              m_buf << (type = s[i++]);
              if (i < n)
                {
                  if (s[i] == '8')
                    {
                      bitwidth = 8;
                      if (type == 'd')
                        val_type = octave_value (int8NDArray ());
                      else
                        val_type = octave_value (uint8NDArray ());
                      m_buf << s[i++];
                    }
                  else if (s[i] == '1' && i+1 < n && s[i+1] == '6')
                    {
                      bitwidth = 16;
                      if (type == 'd')
                        val_type = octave_value (int16NDArray ());
                      else
                        val_type = octave_value (uint16NDArray ());
                      m_buf << s[i++];
                      m_buf << s[i++];
                    }
                  else if (s[i] == '3' && i+1 < n && s[i+1] == '2')
                    {
                      done = false;       // use default size below
                      m_buf << s[i++];
                      m_buf << s[i++];
                    }
                  else if (s[i] == '6' && i+1 < n && s[i+1] == '4')
                    {
                      bitwidth = 64;
                      if (type == 'd')
                        val_type = octave_value (int64NDArray ());
                      else
                        val_type = octave_value (uint64NDArray ());
                      m_buf << s[i++];
                      m_buf << s[i++];
                    }
                  else
                    done = false;
                }
              else
                done = false;

              if (! done)
                {
                  bitwidth = 32;
                  if (type == 'd')
                    val_type = octave_value (int32NDArray ());
                  else
                    val_type = octave_value (uint32NDArray ());
                }
              goto fini;
            }

          case 'f':
            m_buf << (type = s[i++]);
            bitwidth = 64;
            if (i < n)
              {
                if (s[i] == '3' && i+1 < n && s[i+1] == '2')
                  {
                    bitwidth = 32;
                    val_type = octave_value (FloatNDArray ());
                    m_buf << s[i++];
                    m_buf << s[i++];
                  }
                else if (s[i] == '6' && i+1 < n && s[i+1] == '4')
                  {
                    val_type = octave_value (NDArray ());
                    m_buf << s[i++];
                    m_buf << s[i++];
                  }
                else
                  val_type = octave_value (NDArray ());
              }
            else
              val_type = octave_value (NDArray ());
            goto fini;

          case 'n':
            m_buf << (type = s[i++]);
            bitwidth = 64;
            val_type = octave_value (NDArray ());
            goto fini;

          case 's': case 'q': case '[': case 'c':
            if (! discard)
              val_type = octave_value (Cell ());
            m_buf << (type = s[i++]);
            has_string = true;
            goto fini;

          fini:
            {
              if (! have_width)
                {
                  if (type == 'c')        // %c defaults to one character
                    width = 1;
                  else
                    width = static_cast<unsigned int> (-1); // others: unlimited
                }

              if (finish_conversion (s, i, n, width, prec, bitwidth, val_type,
                                     discard, type) == 0)
                return;
            }
            break;

          default:
            error ("%s: '%%%c' is not a valid format specifier",
                   who.c_str (), s[i]);
          }

        if (m_nconv < 0)
          break;
      }

    m_nconv = -1;
  }

  // Parse [...] and [^...]
  //
  // Matlab does not expand expressions like A-Z, but they are useful, and
  // so we parse them "carefully".  We treat '-' as a usual character
  // unless both start and end characters are from the same class (upper
  // case, lower case, numeric), or this is not the first '-' in the
  // pattern.
  //
  // Keep both a running list of characters and a mask of which chars have
  // occurred.  The first is efficient for patterns with few characters.
  // The latter is efficient for [^...] patterns.

  std::string
  textscan_format_list::parse_char_class (const std::string& pattern) const
  {
    int len = pattern.length ();
    if (len == 0)
      return "";

    std::string retval (256, '\0');
    std::string mask   (256, '\0');       // number of times chr has been seen

    int in = 0, out = 0;
    unsigned char ch, prev = 0;
    bool flip = false;

    ch = pattern[in];
    if (ch == '^')
      {
        in++;
        flip = true;
      }
    mask[pattern[in]] = '\1';
    retval[out++] = pattern[in++];        // even copy ']' if it is first

    bool prev_was_range = false;          // disallow "a-m-z" as a pattern
    bool prev_prev_was_range = false;
    for (; in < len; in++)
      {
        bool was_range = false;
        ch = pattern[in];
        if (ch == ']')
          break;

        if (prev == '-' && in > 1 && isalnum (ch) && ! prev_prev_was_range)
          {
            unsigned char start_of_range = pattern[in-2];
            if (start_of_range < ch
                && ((isupper (ch) && isupper (start_of_range))
                    || (islower (ch) && islower (start_of_range))
                    || (isdigit (ch) && isdigit (start_of_range))
                    || mask['-'] > 1))    // not the first '-'
              {
                was_range = true;
                out--;
                mask['-']--;
                for (int i = start_of_range; i <= ch; i++)
                  {
                    if (mask[i] == '\0')
                      {
                        mask[i] = '\1';
                        retval[out++] = i;
                      }
                  }
              }
          }
        if (! was_range)
          {
            if (mask[ch]++ == 0)
              retval[out++] = ch;
            else if (ch != '-')
              warning_with_id ("Octave:textscan-pattern",
                               "%s: [...] contains two '%c's",
                               who.c_str (), ch);

            if (prev == '-' && mask['-'] >= 2)
              warning_with_id
                ("Octave:textscan-pattern",
                 "%s: [...] contains two '-'s outside range expressions",
                 who.c_str ());
          }
        prev = ch;
        prev_prev_was_range = prev_was_range;
        prev_was_range = was_range;
      }

    if (flip)                             // [^...]
      {
        out = 0;
        for (int i = 0; i < 256; i++)
          if (! mask[i])
            retval[out++] = i;
      }

    retval.resize (out);

    return retval;
  }

  int
  textscan_format_list::finish_conversion (const std::string& s, std::size_t& i,
                                           std::size_t n, unsigned int width,
                                           int prec, int bitwidth,
                                           octave_value& val_type, bool discard,
                                           char& type)
  {
    int retval = 0;

    std::string char_class;

    std::size_t beg_idx = std::string::npos;
    std::size_t end_idx = std::string::npos;

    if (type != '%')
      {
        m_nconv++;
        if (type == '[')
          {
            if (i < n)
              {
                beg_idx = i;

                if (s[i] == '^')
                  {
                    type = '^';
                    m_buf << s[i++];

                    if (i < n)
                      {
                        beg_idx = i;

                        if (s[i] == ']')
                          m_buf << s[i++];
                      }
                  }
                else if (s[i] == ']')
                  m_buf << s[i++];
              }

            while (i < n && s[i] != ']')
              m_buf << s[i++];

            if (i < n && s[i] == ']')
              {
                end_idx = i-1;
                m_buf << s[i++];
              }

            if (s[i-1] != ']')
              retval = m_nconv = -1;
          }
      }

    if (m_nconv >= 0)
      {
        if (beg_idx != std::string::npos && end_idx != std::string::npos)
          char_class = parse_char_class (s.substr (beg_idx,
                                                   end_idx - beg_idx + 1));

        add_elt_to_list (width, prec, bitwidth, val_type, discard, type,
                         char_class);
      }

    return retval;
  }

  void
  textscan_format_list::printme (void) const
  {
    std::size_t n = numel ();

    for (std::size_t i = 0; i < n; i++)
      {
        textscan_format_elt *elt = m_fmt_elts[i];

        std::cerr
          << "width:      " << elt->width << "\n"
          << "digits      " << elt->prec << "\n"
          << "bitwidth:   " << elt->bitwidth << "\n"
          << "discard:    " << elt->discard << "\n"
          << "type:       ";

        if (elt->type == textscan_format_elt::literal_conversion)
          std::cerr << "literal text\n";
        else if (elt->type == textscan_format_elt::whitespace_conversion)
          std::cerr << "whitespace\n";
        else
          std::cerr << elt->type << "\n";

        std::cerr
          << "char_class: '" << undo_string_escapes (elt->char_class) << "'\n"
          << "text:       '" << undo_string_escapes (elt->text) << "'\n\n";
      }
  }

  // If FORMAT is explicitly "", it is assumed to be "%f" repeated enough
  // times to read the first row of the file.  Set it now.

  int
  textscan_format_list::read_first_row (delimited_stream& is, textscan& ts)
  {
    // Read first line and strip end-of-line, which may be two characters
    std::string first_line (20, ' ');

    is.getline (first_line, static_cast<char> (ts.m_eol2));

    if (! first_line.empty () && first_line.back () == ts.m_eol1)
      first_line.pop_back ();

    std::istringstream strstr (first_line);
    delimited_stream ds (strstr, is);

    dim_vector dv (1, 1);     // initial size of each output_container
    Complex val;
    octave_value val_type;
    m_nconv = 0;
    int max_empty = 1000;     // failsafe, if ds fails but not with eof
    int retval = 0;

    // read line, creating output_container as we go
    while (! ds.eof ())
      {
        bool already_skipped_delim = false;
        ts.skip_whitespace (ds, false);
        ds.progress_benchmark ();
        ts.scan_complex (ds, *m_fmt_elts[0], val);
        if (ds.fail ())
          {
            ds.clear (ds.rdstate () & ~std::ios::failbit);

            if (ds.eof ())
              break;

            // Unless this was a missing value (i.e., followed by a delimiter),
            // return with an error status.
            ts.skip_delim (ds);
            if (ds.no_progress ())
              {
                retval = 4;
                break;
              }
            already_skipped_delim = true;

            val = ts.m_empty_value.scalar_value ();

            if (! --max_empty)
              break;
          }

        if (val.imag () == 0)
          val_type = octave_value (NDArray (dv, val.real ()));
        else
          val_type = octave_value (ComplexNDArray (dv, val));

        m_output_container.push_back (val_type);

        if (! already_skipped_delim)
          ts.skip_delim (ds);

        if (ds.no_progress ())
          break;

        m_nconv++;
      }

    m_output_container.pop_front (); // discard empty element from constructor

    // Create fmt_list now that the size is known
    for (octave_idx_type i = 1; i < m_nconv; i++)
      m_fmt_elts.push_back (new textscan_format_elt (*m_fmt_elts[0]));

    return retval;             // May have returned 4 above.
  }

  textscan::textscan (const std::string& who_arg, const std::string& encoding)
    : m_who (who_arg), m_encoding (encoding), m_buf (), m_whitespace_table (),
      m_delim_table (), m_delims (), m_comment_style (), m_comment_len (0),
      m_comment_char (-2), m_buffer_size (0), m_date_locale (),
      m_inf_nan (init_inf_nan ()),
      m_empty_value (numeric_limits<double>::NaN ()),
      m_exp_chars ("edED"), m_header_lines (0), m_treat_as_empty (),
      m_treat_as_empty_len (0), m_whitespace (" \b\t"), m_eol1 ('\r'),
      m_eol2 ('\n'), m_return_on_error (1), m_collect_output (false),
      multiple_delims_as_one (false), m_default_exp (true), m_lines (0)
  { }

  octave_value
  textscan::scan (std::istream& isp, const std::string& fmt,
                  octave_idx_type ntimes, const octave_value_list& options,
                  octave_idx_type& count)
  {
    textscan_format_list fmt_list (fmt);

    parse_options (options, fmt_list);

    octave_value result = do_scan (isp, fmt_list, ntimes);

    // FIXME: this is probably not the best way to get count.  The
    // position could easily be larger than octave_idx_type when using
    // 32-bit indexing.

    std::ios::iostate state = isp.rdstate ();
    isp.clear ();
    count = static_cast<octave_idx_type> (isp.tellg ());
    isp.setstate (state);

    return result;
  }

  octave_value
  textscan::do_scan (std::istream& isp, textscan_format_list& fmt_list,
                     octave_idx_type ntimes)
  {
    octave_value retval;

    if (fmt_list.num_conversions () == -1)
      error ("%s: invalid format specified", m_who.c_str ());

    if (fmt_list.num_conversions () == 0)
      error ("%s: no valid format conversion specifiers", m_who.c_str ());

    // skip the first header_lines
    std::string dummy;
    for (int i = 0; i < m_header_lines && isp; i++)
      getline (isp, dummy, static_cast<char> (m_eol2));

    // Create our own buffered stream, for fast get/putback/tell/seek.

    // First, see how far ahead it should let us look.
    int max_lookahead = std::max ({m_comment_len, m_treat_as_empty_len,
                                   m_delim_len, 3});  // 3 for NaN and Inf

    // Next, choose a buffer size to avoid reading too much, or too often.
    octave_idx_type buf_size = 4096;
    if (m_buffer_size)
      buf_size = m_buffer_size;
    else if (ntimes > 0)
      {
        // Avoid overflow of 80*ntimes...
        buf_size = std::min (buf_size, std::max (ntimes, 80 * ntimes));
        buf_size = std::max (buf_size, ntimes);
      }
    // Finally, create the stream.
    delimited_stream is (isp,
                         (m_delims.empty () ? m_whitespace + "\r\n"
                                            : m_delims),
                         max_lookahead, buf_size);

    // Grow retval dynamically.  "size" is half the initial size
    // (FIXME: Should we start smaller if ntimes is large?)
    octave_idx_type size = ((ntimes < 8 && ntimes >= 0) ? ntimes : 1);
    Array<octave_idx_type> row_idx (dim_vector (1, 2));
    row_idx(1) = 0;

    int err = 0;
    octave_idx_type row = 0;

    if (multiple_delims_as_one)           // bug #44750?
      skip_delim (is);

    int done_after;  // Number of columns read when EOF seen.

    // If FORMAT explicitly "", read first line and see how many "%f" match
    if (fmt_list.set_from_first)
      {
        err = fmt_list.read_first_row (is, *this);
        m_lines = 1;

        done_after = fmt_list.numel () + 1;
        if (! err)
          row = 1;  // the above puts the first line into fmt_list.out_buf ()
      }
    else
      done_after = fmt_list.out_buf ().size () + 1;

    std::list<octave_value> out = fmt_list.out_buf ();

    // We will later merge adjacent columns of the same type.
    // Check now which columns to merge.
    // Reals may become complex, and so we can't trust types
    // after reading in data.
    // If the format was "", that conversion may already have happened,
    // so force all to be merged (as all are %f).
    bool merge_with_prev[fmt_list.numel ()];
    int conv = 0;
    if (m_collect_output)
      {
        int prev_type = -1;
        for (const auto& col : out)
          {
            if (col.type_id () == prev_type
                || (fmt_list.set_from_first && prev_type != -1))
              merge_with_prev[conv++] = true;
            else
              merge_with_prev[conv++] = false;

            prev_type = col.type_id ();
          }
      }

    // This should be caught by earlier code, but this avoids a possible
    // infinite loop below.
    if (fmt_list.num_conversions () == 0)
      error ("%s: No conversions specified", m_who.c_str ());

    // Read the data.  This is the main loop.
    if (! err)
      {
        for (/* row set ~30 m_lines above */;
             row < ntimes || ntimes == -1;
             row++)
          {
            if (row == 0 || row >= size)
              {
                size += (size+1);
                for (auto& col : out)
                  col = col.resize (dim_vector (size, 1), 0);
              }

            row_idx(0) = row;
            err = read_format_once (is, fmt_list, out, row_idx, done_after);

            if ((err & ~1) > 0 || ! is || (m_lines >= ntimes && ntimes > -1))
              break;
          }
      }

    if ((err & 4) && ! m_return_on_error)
      error ("%s: Read error in field %d of row %" OCTAVE_IDX_TYPE_FORMAT,
             m_who.c_str (), done_after + 1, row + 1);

    // If file does not end in EOL, do not pad columns with NaN.
    bool uneven_columns = false;
    if (err & 4)
      uneven_columns = true;
    else if (isp.eof ())
      {
        isp.clear ();
        isp.seekg (-1, std::ios_base::end);
        int last_char = isp.get ();
        isp.setstate (isp.eofbit);
        uneven_columns = (last_char != m_eol1 && last_char != m_eol2);
      }

    // convert return value to Cell array
    Array<octave_idx_type> ra_idx (dim_vector (1, 2));

    // (err & 1) means "error, and no columns read this row
    // FIXME: This may redundant now that done_after=0 says the same
    if (err & 1)
      done_after = out.size () + 1;

    int valid_rows = (row == ntimes
                      ? ntimes
                      : ((err & 1) && (err & 8)) ? row : row+1);
    dim_vector dv (valid_rows, 1);

    ra_idx(0) = 0;
    int i = 0;
    if (! m_collect_output)
      {
        retval = Cell (dim_vector (1, out.size ()));
        for (auto& col : out)
          {
            // trim last columns if that was requested
            if (i == done_after && uneven_columns)
              dv = dim_vector (std::max (valid_rows - 1, 0), 1);

            ra_idx(1) = i;
            retval = cat_op (retval, octave_value (Cell (col.resize (dv, 0))),
                             ra_idx);
            i++;
          }
      }
    else  // group adjacent cells of the same type into a single cell
      {
        octave_value cur;                // current cell, accumulating columns
        octave_idx_type group_size = 0;  // columns in this cell
        int prev_type = -1;

        conv = 0;
        retval = Cell ();
        for (auto& col : out)
          {
            if (! merge_with_prev[conv++])  // including first time
              {
                if (prev_type != -1)
                  {
                    ra_idx(1) = i++;
                    retval = cat_op (retval, octave_value (Cell (cur)), ra_idx);
                  }
                cur = octave_value (col.resize (dv, 0));
                group_size = 1;
                prev_type = col.type_id ();
              }
            else
              {
                ra_idx(1) = group_size++;
                cur = cat_op (cur, octave_value (col.resize (dv, 0)), ra_idx);
              }
          }
        ra_idx(1) = i;
        retval = cat_op (retval, octave_value (Cell (cur)), ra_idx);
      }

    return retval;
  }

  // Read a double considering the "precision" field of FMT and the
  // EXP_CHARS option of OPTIONS.

  double
  textscan::read_double (delimited_stream& is,
                         const textscan_format_elt& fmt) const
  {
    int sign = 1;
    unsigned int width_left = fmt.width;
    double retval = 0;
    bool valid = false;         // syntactically correct double?

    int ch = is.peek_undelim ();

    if (ch == '+')
      {
        is.get ();
        ch = is.peek_undelim ();
        if (width_left)
          width_left--;
      }
    else if (ch == '-')
      {
        sign = -1;
        is.get ();
        ch = is.peek_undelim ();
        if (width_left)
          width_left--;
      }

    // Read integer part
    if (ch != '.')
      {
        if (ch >= '0' && ch <= '9')       // valid if at least one digit
          valid = true;
        while (width_left-- && is && (ch = is.get ()) >= '0' && ch <= '9')
          retval = retval * 10 + (ch - '0');
        width_left++;
      }

    // Read fractional part, up to specified precision
    if (ch == '.' && width_left)
      {
        double multiplier = 1;
        int precision = fmt.prec;
        int i;

        width_left--;                  // Consider width of '.'

        if (precision == -1)
          precision = 1<<30;           // FIXME: Should be MAXINT

        if (! valid)                   // if there was nothing before '.'...
          is.get ();                   // ...ch was a "peek", not "get".

        for (i = 0; i < precision; i++)
          {
            if (width_left-- && is && (ch = is.get ()) >= '0' && ch <= '9')
              retval += (ch - '0') * (multiplier *= 0.1);
            else
              {
                width_left++;
                break;
              }
          }

        // round up if we truncated and the next digit is >= 5
        if ((i == precision || ! width_left) && (ch = is.get ()) >= '5'
            && ch <= '9')
          retval += multiplier;

        if (i > 0)
          valid = true;           // valid if at least one digit after '.'
        else if (! valid)         // if there was nothing before and after '.'
          {
            is.putback (ch);
            ch = '.';
          }

        // skip remainder after '.', to field width, to look for exponent
        if (i == precision)
          while (width_left-- && is && (ch = is.get ()) >= '0' && ch <= '9')
            ;  // discard

        width_left++;
      }

    // look for exponent part in, e.g.,  6.023E+23
    bool used_exp = false;
    if (valid && width_left > 1 && m_exp_chars.find (ch) != std::string::npos)
      {
        int ch1 = is.peek_undelim ();
        if (ch1 == '-' || ch1 == '+' || (ch1 >= '0' && ch1 <= '9'))
          {
            // if 1.0e+$ or some such, this will set failbit, as we want
            width_left--;                         // count "E"
            int exp = 0;
            int exp_sign = 1;
            if (ch1 == '+')
              {
                width_left--;
                is.get ();
              }
            else if (ch1 == '-')
              {
                width_left--;
                exp_sign = -1;
                is.get ();
              }
            valid = false;
            while (width_left-- && is && (ch = is.get_undelim ()) >= '0' && ch <= '9')
              {
                exp = exp*10 + ch - '0';
                valid = true;
              }
            width_left++;
            if (ch != std::istream::traits_type::eof () && width_left)
              is.putback (ch);

            double multiplier = pown (10, exp);
            if (exp_sign > 0)
              retval *= multiplier;
            else
              retval /= multiplier;

            used_exp = true;
          }
      }
    is.clear ();
    if (! used_exp && ch != std::istream::traits_type::eof () && width_left)
      is.putback (ch);

    // Check for +/- inf and NaN
    if (! valid && width_left >= 3 && is.remaining () >= 3)
      {
        int i = lookahead (is, m_inf_nan, 3, false);  // false->case insensitive
        if (i == 0)
          {
            retval = numeric_limits<double>::Inf ();
            valid = true;
          }
        else if (i == 1)
          {
            retval = numeric_limits<double>::NaN ();
            valid = true;
          }
      }

    if (! valid)
      is.setstate (std::ios::failbit);
    else
      is.setstate (is.rdstate () & ~std::ios::failbit);

    return retval * sign;
  }

  // Read a single number: real, complex, inf, NaN, possibly with limited
  // precision.  Calls to this should be preceded by skip_whitespace.
  // Calling that inside scan_complex would violate its const declaration.

  void
  textscan::scan_complex (delimited_stream& is, const textscan_format_elt& fmt,
                          Complex& val) const
  {
    double im = 0;
    double re = 0;
    bool as_empty = false;  // did we fail but match a "treat_as_empty" string?
    bool inf = false;

    int ch = is.peek_undelim ();
    if (ch == '+' || ch == '-')   // check for [+-][ij] with no coefficients
      {
        ch = is.get ();
        int ch2 = is.peek_undelim ();
        if (ch2 == 'i' || ch2 == 'j')
          {
            double value = 1;
            is.get ();
            // Check not -inf
            if (is.peek_undelim () == 'n')
              {
                char *pos = is.tellg ();
                std::ios::iostate state = is.rdstate ();

                is.get ();
                ch2 = is.get_undelim ();
                if (ch2 == 'f')
                  {
                    inf = true;
                    re = (ch == '+' ? numeric_limits<double>::Inf ()
                                    : -numeric_limits<double>::Inf ());
                    value = 0;
                  }
                else
                  {
                    is.clear (state);
                    // FIXME: Buffer might have refreshed.
                    //        pos might no longer be valid.
                    is.seekg (pos);   // reset to position before look-ahead
                  }
              }

            im = (ch == '+') ? value : -value;
          }
        else
          is.putback (ch);
      }

    if (! im && ! inf)        // if not [+-][ij] or [+-]inf, read real normally
      {
        char *pos = is.tellg ();
        std::ios::iostate state = is.rdstate ();
        //re = read_value<double> (is);
        // FIXME: read_double might refresh the buffer.  So seekg might be off.
        re = read_double (is, fmt);

        // check for "treat as empty" string
        if (m_treat_as_empty.numel ()
            && (is.fail () || math::is_NaN_or_NA (Complex (re))
                || re == numeric_limits<double>::Inf ()))
          {

            for (int i = 0; i < m_treat_as_empty.numel (); i++)
              {
                if (ch == m_treat_as_empty (i).string_value ()[0])
                  {
                    as_empty = true;  // first char matches, so read the lot
                    break;
                  }
              }
            if (as_empty)             // if first char matched...
              {
                as_empty = false;     // ...look for the whole string

                is.clear (state);     // treat_as_empty "-" causes partial read
                is.seekg (pos);       // reset to position before failed read

                // treat_as_empty strings may be different sizes.
                // Read ahead longest, put it all back, then re-read the string
                // that matches.
                std::string look_buf (m_treat_as_empty_len, '\0');
                char *look = is.read (&look_buf[0], look_buf.size (), pos);

                is.clear (state);
                is.seekg (pos);        // reset to position before look-ahead
                                       // FIXME: is.read could invalidate pos

                for (int i = 0; i < m_treat_as_empty.numel (); i++)
                  {
                    std::string s = m_treat_as_empty (i).string_value ();
                    if (! strncmp (s.c_str (), look, s.size ()))
                      {
                        as_empty = true;
                        // read just the right amount
                        is.read (&look_buf[0], s.size (), pos);
                        break;
                      }
                  }
              }
          }

        if (! is.eof () && ! as_empty)
          {
            state = is.rdstate ();   // before tellg, since that fails at EOF

            ch = is.peek_undelim ();
            // ch == EOF if read failed; no need to chk fail
            if (ch == 'i' || ch == 'j')           // pure imaginary
              {
                is.get ();
                im = re;
                re = 0;
              }
            else if (ch == '+' || ch == '-')      // see if it is real+imag[ij]
              {
                // save stream state in case we have to restore it
                pos   = is.tellg ();
                state = is.rdstate ();

                //im = read_value<double> (is);
                // FIXME: read_double might refresh the buffer.
                //        So seekg might be off after this.
                im = read_double (is, fmt);
                if (is.fail ())
                  im = 1;

                if (is.peek_undelim () == 'i' || is.peek_undelim () == 'j')
                  is.get ();
                else
                  {
                    im = 0;           // no valid imaginary part.  Restore state
                    is.clear (state); // eof shouldn't cause fail.
                    is.seekg (pos);
                  }
              }
            else if (is.eof ())       // we've read enough to be a "valid" read
              is.clear (state);       // failed peek shouldn't cause fail
          }
      }
    if (as_empty)
      val = m_empty_value.scalar_value ();
    else
      val = Complex (re, im);
  }

  // Return in VAL the run of characters from IS NOT contained in PATTERN.

  int
  textscan::scan_caret (delimited_stream& is, const std::string& pattern,
                        std::string& val) const
  {
    int c1 = std::istream::traits_type::eof ();
    std::ostringstream obuf;   // FIXME: is this optimized for growing?

    while (is && ((c1 = (is && ! is.eof ())
                   ? is.get_undelim ()
                   : std::istream::traits_type::eof ())
                  != std::istream::traits_type::eof ())
           && pattern.find (c1) == std::string::npos)
      obuf << static_cast<char> (c1);

    val = obuf.str ();

    if (c1 != std::istream::traits_type::eof ())
      is.putback (c1);

    return c1;
  }

  // Read until one of the strings in DELIMITERS is found.  For
  // efficiency, ENDS is a list of the last character of each delimiter.

  std::string
  textscan::read_until (delimited_stream& is, const Cell& delimiters,
                        const std::string& ends) const
  {
    std::string retval ("");
    bool done = false;
    do
      {
        // find sequence ending with an ending char
        std::string next;
        scan_caret (is, ends.c_str (), next);
        retval = retval + next;   // FIXME: could use repeated doubling of size

        int last = (! is.eof ()
                    ? is.get_undelim () : std::istream::traits_type::eof ());

        if (last != std::istream::traits_type::eof ())
          {
            if (last == m_eol1 || last == m_eol2)
              break;

            retval = retval + static_cast<char> (last);
            for (int i = 0; i < delimiters.numel (); i++)
              {
                std::string delim = delimiters(i).string_value ();
                std::size_t start = (retval.length () > delim.length ()
                                     ? retval.length () - delim.length ()
                                     : 0);
                std::string may_match = retval.substr (start);
                if (may_match == delim)
                  {
                    done = true;
                    retval = retval.substr (0, start);
                    if (start == 0)
                      is.putback (last);
                    break;
                  }
              }
          }
      }
    while (! done && is && ! is.eof ());

    return retval;
  }

  // Read stream until either fmt.width chars have been read, or
  // options.delimiter has been found.  Does *not* rely on fmt being 's'.
  // Used by formats like %6f to limit to 6.

  void
  textscan::scan_string (delimited_stream& is, const textscan_format_elt& fmt,
                         std::string& val) const
  {
    if (m_delim_list.isempty ())
      {
        unsigned int i = 0;
        unsigned int width = fmt.width;

        for (i = 0; i < width; i++)
          {
            // Grow string in an exponential fashion if necessary.
            if (i >= val.length ())
              val.append (std::max (val.length (),
                                    static_cast<std::size_t> (16)), '\0');

            int ch = is.get_undelim ();
            if (is_delim (ch) || ch == std::istream::traits_type::eof ())
              {
                is.putback (ch);
                break;
              }
            else
              val[i] = ch;
          }
        val = val.substr (0, i);          // trim pre-allocation
      }
    else  // Cell array of multi-character delimiters
      {
        std::string ends (m_delim_list.numel () + 2, '\0');
        int i;
        for (i = 0; i < m_delim_list.numel (); i++)
          {
            std::string tmp = m_delim_list(i).string_value ();
            ends[i] = tmp.back ();
          }
        ends[i++] = m_eol1;
        ends[i++] = m_eol2;
        val = textscan::read_until (is, m_delim_list, ends);
      }

    // convert from codepage
    if (m_encoding.compare ("utf-8"))
      val = string::u8_from_encoding ("textscan", val, m_encoding);
  }

  // Return in VAL the run of characters from IS contained in PATTERN.

  int
  textscan::scan_bracket (delimited_stream& is, const std::string& pattern,
                          std::string& val) const
  {
    int c1 = std::istream::traits_type::eof ();
    std::ostringstream obuf;              // Is this optimized for growing?

    while (is && pattern.find (c1 = is.get_undelim ()) != std::string::npos)
      obuf << static_cast<char> (c1);

    val = obuf.str ();
    if (c1 != std::istream::traits_type::eof ())
      is.putback (c1);
    return c1;
  }

  // Return in VAL a string, either delimited by whitespace/delimiters, or
  // enclosed in a pair of double quotes ("...").  Enclosing quotes are
  // removed.  A consecutive pair "" is inserted into VAL as a single ".

  void
  textscan::scan_qstring (delimited_stream& is, const textscan_format_elt& fmt,
                          std::string& val)
  {
    skip_whitespace (is);

    if (is.peek_undelim () != '"')
      scan_string (is, fmt, val);
    else
      {
        is.get ();
        scan_caret (is, R"(")", val);     // read everything until "
        is.get ();                        // swallow "

        while (is && is.peek_undelim () == '"')  // if double ",
          {                                      // insert one in stream,
            is.get ();                           // keep looking for single "
            std::string val1;
            scan_caret (is, R"(")", val1);
            val = val + '"' + val1;
            is.get_undelim ();
          }
      }

    // convert from codepage
    if (m_encoding.compare ("utf-8"))
      val = string::u8_from_encoding ("textscan", val, m_encoding);
  }

  // Read from IS into VAL a string of the next fmt.width characters,
  // including any whitespace or delimiters.

  void
  textscan::scan_cstring (delimited_stream& is, const textscan_format_elt& fmt,
                          std::string& val) const
  {
    val.resize (fmt.width);

    for (unsigned int i = 0; is && i < fmt.width; i++)
      {
        int ch = is.get_undelim ();
        if (ch != std::istream::traits_type::eof ())
          val[i] = ch;
        else
          {
            val.resize (i);
            break;
          }
      }

    // convert from codepage
    if (m_encoding.compare ("utf-8"))
      val = string::u8_from_encoding ("textscan", val, m_encoding);
  }

  //  Read a single '%...' conversion and place it in position ROW of OV.

  void
  textscan::scan_one (delimited_stream& is, const textscan_format_elt& fmt,
                      octave_value& ov, Array<octave_idx_type> row)
  {
    skip_whitespace (is);

    is.clear ();

    octave_value val;
    if (fmt.numeric)
      {
        if (fmt.type == 'f' || fmt.type == 'n')
          {
            Complex v;
            skip_whitespace (is);
            scan_complex (is, fmt, v);

            if (! fmt.discard && ! is.fail ())
              {
                if (fmt.bitwidth == 64)
                  {
                    if (ov.isreal () && v.imag () == 0)
                      ov.internal_rep ()->fast_elem_insert (row(0), v.real ());
                    else
                      {
                        if (ov.isreal ())  // cat does type conversion
                          ov = cat_op (ov, octave_value (v), row);
                        else
                          ov.internal_rep ()->fast_elem_insert (row(0), v);
                      }
                  }
                else
                  {
                    if (ov.isreal () && v.imag () == 0)
                      ov.internal_rep ()->fast_elem_insert (row(0),
                                                            float (v.real ()));
                    else
                      {
                        if (ov.isreal ())  // cat does type conversion
                          ov = cat_op (ov, octave_value (v), row);
                        else
                          ov.internal_rep ()->fast_elem_insert (row(0),
                                                                FloatComplex (v));
                      }
                  }
              }
          }
        else
          {
            double v;    // Matlab docs say 1e30 etc should be valid for %d and
                         // 1000 as a %d8 should be 127, so read as double.
                         // Some loss of precision for d64 and u64.
            skip_whitespace (is);
            v = read_double (is, fmt);
            if (! fmt.discard && ! is.fail ())
              switch (fmt.bitwidth)
                {
                case 64:
                  switch (fmt.type)
                    {
                    case 'd':
                      {
                        octave_int64 vv = v;
                        ov.internal_rep ()->fast_elem_insert (row(0), vv);
                      }
                      break;

                    case 'u':
                      {
                        octave_uint64 vv = v;
                        ov.internal_rep ()->fast_elem_insert (row(0), vv);
                      }
                      break;
                    }
                  break;

                case 32:
                  switch (fmt.type)
                    {
                    case 'd':
                      {
                        octave_int32 vv = v;
                        ov.internal_rep ()->fast_elem_insert (row(0), vv);
                      }
                      break;

                    case 'u':
                      {
                        octave_uint32 vv = v;
                        ov.internal_rep ()->fast_elem_insert (row(0), vv);
                      }
                      break;
                    }
                  break;

                case 16:
                  if (fmt.type == 'd')
                    {
                      octave_int16 vv = v;
                      ov.internal_rep ()->fast_elem_insert (row(0), vv);
                    }
                  else
                    {
                      octave_uint16 vv = v;
                      ov.internal_rep ()->fast_elem_insert (row(0), vv);
                    }
                  break;

                case 8:
                  if (fmt.type == 'd')
                    {
                      octave_int8 vv = v;
                      ov.internal_rep ()->fast_elem_insert (row(0), vv);
                    }
                  else
                    {
                      octave_uint8 vv = v;
                      ov.internal_rep ()->fast_elem_insert (row(0), vv);
                    }
                  break;
                }
          }

        if (is.fail () & ! fmt.discard)
          ov = cat_op (ov, m_empty_value, row);
      }
    else
      {
        std::string vv ("        ");      // initial buffer.  Grows as needed
        switch (fmt.type)
          {
          case 's':
            scan_string (is, fmt, vv);
            break;

          case 'q':
            scan_qstring (is, fmt, vv);
            break;

          case 'c':
            scan_cstring (is, fmt, vv);
            break;

          case '[':
            scan_bracket (is, fmt.char_class.c_str (), vv);
            break;

          case '^':
            scan_caret   (is, fmt.char_class.c_str (), vv);
            break;
          }

        if (! fmt.discard)
          ov.internal_rep ()->fast_elem_insert (row (0),
                                                Cell (octave_value (vv)));

        // FIXME: why does failbit get set at EOF, instead of eofbit?
        if (! vv.empty ())
          is.clear (is.rdstate () & ~std::ios_base::failbit);
      }

    is.field_done ();
  }

  // Read data corresponding to the entire format string once, placing the
  // values in row ROW of retval.

  int
  textscan::read_format_once (delimited_stream& is,
                              textscan_format_list& fmt_list,
                              std::list<octave_value>& retval,
                              Array<octave_idx_type> row, int& done_after)
  {
    const textscan_format_elt *elem = fmt_list.first ();
    auto out = retval.begin ();
    bool no_conversions = true;
    bool done = false;
    bool conversion_failed = false;       // Record for ReturnOnError
    bool nothing_worked = true;

    octave_quit ();

    for (std::size_t i = 0; i < fmt_list.numel (); i++)
      {
        bool this_conversion_failed = false;

        // Clear fail of previous numeric conversions.
        is.clear ();

        switch (elem->type)
          {
          case 'C':
          case 'D':
            warning ("%s: conversion %c not yet implemented",
                     m_who.c_str (), elem->type);
            break;

          case 'u':
          case 'd':
          case 'f':
          case 'n':
          case 's':
          case '[':
          case '^':
          case 'q':
          case 'c':
            scan_one (is, *elem, *out, row);
            break;

          case textscan_format_elt::literal_conversion :
            match_literal (is, *elem);
            break;

          default:
            error ("Unknown format element '%c'", elem->type);
          }

        if (! is.fail ())
          {
            if (! elem->discard)
              no_conversions = false;
          }
        else
          {
            is.clear (is.rdstate () & ~std::ios::failbit);

            if (! is.eof ())
              {
                if (m_delim_list.isempty ())
                  {
                    if (! is_delim (is.peek_undelim ()))
                      this_conversion_failed = true;
                  }
                else  // Cell array of multi-character delimiters
                  {
                    char *pos = is.tellg ();
                    if (-1 == lookahead (is, m_delim_list, m_delim_len))
                      this_conversion_failed = true;
                    is.clear ();
                    is.seekg (pos);     // reset to position before look-ahead
                  }
              }
          }

        if (! elem->discard)
          out++;

        elem = fmt_list.next ();
        char *pos = is.tellg ();

        // Skip delimiter before reading the next fmt conversion,
        // unless the fmt is a string literal which begins with a delimiter,
        // in which case the literal must match everything.  Bug #58008
        if (elem->type != textscan_format_elt::literal_conversion)
          skip_delim (is);
        else if (! is_delim (elem->text[0]))
          skip_delim (is);

        if (is.eof ())
          {
            if (! done)
              done_after = i+1;

            // note EOF, but process others to get empty_val.
            done = true;
          }

        if (this_conversion_failed)
          {
            if (is.tellg () == pos && ! conversion_failed)
              {
                // done_after = first failure
                done_after = i; // note fail, but parse others to get empty_val
                conversion_failed = true;
              }
            else
              this_conversion_failed = false;
          }
        else if (! done && ! conversion_failed)
          nothing_worked = false;
      }

    if (done)
      is.setstate (std::ios::eofbit);

    return no_conversions
           + (is.eof () ? 2 : 0)
           + (conversion_failed ? 4 : 0)
           + (nothing_worked ? 8 : 0);

  }

  void
  textscan::parse_options (const octave_value_list& args,
                           textscan_format_list& fmt_list)
  {
    int last = args.length ();
    int n = last;

    if (n & 1)
      error ("%s: %d parameters given, but only %d values",
             m_who.c_str (), n-n/2, n/2);

    m_delim_len = 1;
    bool have_delims = false;
    for (int i = 0; i < last; i += 2)
      {
        std::string param = args(i).xstring_value ("%s: Invalid parameter type <%s> for parameter %d",
                                                   m_who.c_str (),
                                                   args(i).type_name ().c_str (),
                                                   i/2 + 1);
        std::transform (param.begin (), param.end (), param.begin (), ::tolower);

        if (param == "delimiter")
          {
            bool invalid = true;
            if (args(i+1).is_string ())
              {
                invalid = false;
                have_delims = true;
                m_delims = args(i+1).string_value ();
                if (args(i+1).is_sq_string ())
                  m_delims = do_string_escapes (m_delims);
              }
            else if (args(i+1).iscell ())
              {
                invalid = false;
                m_delim_list = args(i+1).cell_value ();
                m_delim_table = " ";  // non-empty, to flag non-default delim

                // Check that all elements are strings, and find max length
                for (int j = 0; j < m_delim_list.numel (); j++)
                  {
                    if (! m_delim_list(j).is_string ())
                      invalid = true;
                    else
                      {
                        if (m_delim_list(j).is_sq_string ())
                          m_delim_list(j) = do_string_escapes (m_delim_list(j)
                                                               .string_value ());
                        octave_idx_type len = m_delim_list(j).string_value ()
                                              .length ();
                        m_delim_len = std::max (static_cast<int> (len),
                                                m_delim_len);
                      }
                  }
              }
            if (invalid)
              error ("%s: Delimiters must be either a string or cell array of strings",
                     m_who.c_str ());
          }
        else if (param == "commentstyle")
          {
            if (args(i+1).is_string ())
              {
                // check here for names like "C++", "C", "shell", ...?
                m_comment_style = Cell (args(i+1));
              }
            else if (args(i+1).iscell ())
              {
                m_comment_style = args(i+1).cell_value ();
                int len = m_comment_style.numel ();
                if ((len >= 1 && ! m_comment_style (0).is_string ())
                    || (len >= 2 && ! m_comment_style (1).is_string ())
                    || (len >= 3))
                  error ("%s: CommentStyle must be either a string or cell array of one or two strings",
                         m_who.c_str ());
              }
            else
              error ("%s: CommentStyle must be either a string or cell array of one or two strings",
                     m_who.c_str ());

            // How far ahead do we need to look to detect an open comment
            // and which character do we look for?
            if (m_comment_style.numel () >= 1)
              {
                m_comment_len  = m_comment_style (0).string_value ().size ();
                m_comment_char = m_comment_style (0).string_value ()[0];
              }
          }
        else if (param == "treatasempty")
          {
            bool invalid = false;
            if (args(i+1).is_string ())
              {
                m_treat_as_empty = Cell (args(i+1));
                m_treat_as_empty_len = args(i+1).string_value ().size ();
              }
            else if (args(i+1).iscell ())
              {
                m_treat_as_empty = args(i+1).cell_value ();
                for (int j = 0; j < m_treat_as_empty.numel (); j++)
                  if (! m_treat_as_empty (j).is_string ())
                    invalid = true;
                  else
                    {
                      int k = m_treat_as_empty (j).string_value ().size ();
                      if (k > m_treat_as_empty_len)
                        m_treat_as_empty_len = k;
                    }
              }
            if (invalid)
              error ("%s: TreatAsEmpty must be either a string or cell array of one or two strings",
                     m_who.c_str ());

            // FIXME: Ensure none is a prefix of a later one.  Sort by length?
          }
        else if (param == "collectoutput")
          {
            m_collect_output = args(i+1).xbool_value ("%s: CollectOutput must be logical or numeric", m_who.c_str ());
          }
        else if (param == "emptyvalue")
          {
            m_empty_value = args(i+1).xscalar_value ("%s: EmptyValue must be numeric", m_who.c_str ());
          }
        else if (param == "headerlines")
          {
            m_header_lines = args(i+1).xscalar_value ("%s: HeaderLines must be numeric", m_who.c_str ());
          }
        else if (param == "bufsize")
          {
            m_buffer_size = args(i+1).xscalar_value ("%s: BufSize must be numeric", m_who.c_str ());
          }
        else if (param == "multipledelimsasone")
          {
            multiple_delims_as_one = args(i+1).xbool_value ("%s: MultipleDelimsAsOne must be logical or numeric", m_who.c_str ());
          }
        else if (param == "returnonerror")
          {
            m_return_on_error = args(i+1).xbool_value ("%s: ReturnOnError must be logical or numeric", m_who.c_str ());
          }
        else if (param == "whitespace")
          {
            m_whitespace = args(i+1).xstring_value ("%s: Whitespace must be a character string", m_who.c_str ());
          }
        else if (param == "expchars")
          {
            m_exp_chars = args(i+1).xstring_value ("%s: ExpChars must be a character string", m_who.c_str ());
            m_default_exp = false;
          }
        else if (param == "endofline")
          {
            bool valid = true;
            std::string s = args(i+1).xstring_value (R"(%s: EndOfLine must be at most one character or '\r\n')", m_who.c_str ());
            if (args(i+1).is_sq_string ())
              s = do_string_escapes (s);
            int l = s.length ();
            if (l == 0)
              m_eol1 = m_eol2 = -2;
            else if (l == 1)
              m_eol1 = m_eol2 = s.c_str ()[0];
            else if (l == 2)
              {
                m_eol1 = s.c_str ()[0];
                m_eol2 = s.c_str ()[1];
                if (m_eol1 != '\r' || m_eol2 != '\n')    // Why limit it?
                  valid = false;
              }
            else
              valid = false;

            if (! valid)
              error (R"(%s: EndOfLine must be at most one character or '\r\n')",
                     m_who.c_str ());
          }
        else
          error ("%s: unrecognized option '%s'", m_who.c_str (), param.c_str ());
      }

    // Remove any user-supplied delimiter from whitespace list
    for (unsigned int j = 0; j < m_delims.length (); j++)
      {
        m_whitespace.erase (std::remove (m_whitespace.begin (),
                                         m_whitespace.end (),
                                         m_delims[j]),
                            m_whitespace.end ());
      }
    for (int j = 0; j < m_delim_list.numel (); j++)
      {
        std::string delim = m_delim_list(j).string_value ();
        if (delim.length () == 1)
          m_whitespace.erase (std::remove (m_whitespace.begin (),
                                           m_whitespace.end (),
                                           delim[0]),
                              m_whitespace.end ());
      }

    m_whitespace_table = std::string (256, '\0');
    for (unsigned int i = 0; i < m_whitespace.length (); i++)
      m_whitespace_table[m_whitespace[i]] = '1';

    // For Matlab compatibility, add 0x20 to whitespace, unless
    // whitespace is explicitly ignored.
    if (! (m_whitespace.empty () && fmt_list.has_string))
      m_whitespace_table[' '] = '1';

    // Create look-up table of delimiters, based on 'delimiter'
    m_delim_table = std::string (256, '\0');
    if (m_eol1 >= 0 && m_eol1 < 256)
      m_delim_table[m_eol1] = '1';        // EOL is always a delimiter
    if (m_eol2 >= 0 && m_eol2 < 256)
      m_delim_table[m_eol2] = '1';        // EOL is always a delimiter
    if (! have_delims)
      for (unsigned int i = 0; i < 256; i++)
        {
          if (isspace (i))
            m_delim_table[i] = '1';
        }
    else
      for (unsigned int i = 0; i < m_delims.length (); i++)
        m_delim_table[m_delims[i]] = '1';
  }

  // Skip comments, and characters specified by the "Whitespace" option.
  // If EOLstop == true, don't skip end of line.

  int
  textscan::skip_whitespace (delimited_stream& is, bool EOLstop)
  {
    int c1 = std::istream::traits_type::eof ();
    bool found_comment = false;

    do
      {
        found_comment = false;
        int prev = -1;
        while (is
               && (c1 = is.get_undelim ()) != std::istream::traits_type::eof ()
               && ( ( (c1 == m_eol1 || c1 == m_eol2) && ++m_lines && ! EOLstop)
                    || isspace (c1)))
          {
            if (prev == m_eol1 && m_eol1 != m_eol2 && c1 == m_eol2)
              m_lines--;
            prev = c1;
          }

        if (c1 == m_comment_char)           // see if we match an open comment
          {
            // save stream state in case we have to restore it
            char *pos = is.tellg ();
            std::ios::iostate state = is.rdstate ();

            std::string tmp (m_comment_len, '\0');
            char *look = is.read (&tmp[0], m_comment_len-1, pos); // already read first char
            if (is && m_comment_style.numel () > 0
                && ! strncmp (m_comment_style(0).string_value ().substr (1).c_str (),
                              look, m_comment_len-1))
              {
                found_comment = true;

                std::string dummy;
                if (m_comment_style.numel () == 1)  // skip to end of line
                  {
                    std::string eol (3, '\0');
                    eol[0] = m_eol1;
                    eol[1] = m_eol2;

                    scan_caret (is, eol, dummy);
                    c1 = is.get_undelim ();
                    if (c1 == m_eol1 && m_eol1 != m_eol2
                        && is.peek_undelim () == m_eol2)
                      is.get_undelim ();
                    m_lines++;
                  }
                else      // matching pair
                  {
                    std::string end_c = m_comment_style(1).string_value ();
                    // last char of end-comment sequence
                    std::string last = end_c.substr (end_c.size () - 1);
                    std::string may_match ("");
                    do
                      {
                        // find sequence ending with last char
                        scan_caret (is, last, dummy);
                        is.get_undelim ();        // (read LAST itself)

                        may_match = may_match + dummy + last;
                        if (may_match.length () > end_c.length ())
                          {
                            std::size_t start = may_match.length ()
                                                - end_c.length ();
                            may_match = may_match.substr (start);
                          }
                      }
                    while (may_match != end_c && is && ! is.eof ());
                  }
              }
            else  // wasn't really a comment; restore state
              {
                is.clear (state);
                is.seekg (pos);
              }
          }
      }
    while (found_comment);

    if (c1 != std::istream::traits_type::eof ())
      is.putback (c1);

    return c1;
  }

  // See if the next few characters match one of the strings in target.
  // For efficiency, MAX_LEN is the cached longest length of any target.
  // Return -1 if none is found, or the index of the match.

  int
  textscan::lookahead (delimited_stream& is, const Cell& targets, int max_len,
                       bool case_sensitive) const
  {
    // target strings may be different sizes.
    // Read ahead longest, put it all back, then re-read the string
    // that matches.

    char *pos = is.tellg ();

    std::string tmp (max_len, '\0');
    char *look = is.read (&tmp[0], tmp.size (), pos);

    is.clear ();
    is.seekg (pos);              // reset to position before read
                                 // FIXME: pos may be corrupted by is.read

    int i;
    int (*compare)(const char *, const char *, std::size_t);
    compare = (case_sensitive ? strncmp : octave_strncasecmp);

    for (i = 0; i < targets.numel (); i++)
      {
        std::string s = targets (i).string_value ();
        if (! (*compare) (s.c_str (), look, s.size ()))
          {
            is.read (&tmp[0], s.size (), pos); // read just the right amount
            break;
          }
      }

    if (i == targets.numel ())
      i = -1;

    return i;
  }

  // Skip delimiters -- multiple if MultipleDelimsAsOne specified.
  int
  textscan::skip_delim (delimited_stream& is)
  {
    int c1 = skip_whitespace (is);  // Stop once EOL is read
    if (m_delim_list.numel () == 0)   // single character delimiter
      {
        if (is_delim (c1) || c1 == m_eol1 || c1 == m_eol2)
          {
            is.get ();
            if (c1 == m_eol1 && is.peek_undelim () == m_eol2)
              is.get ();          // if \r\n, skip the \n too.

            if (multiple_delims_as_one)
              {
                int prev = -1;
                // skip multiple delims.
                // Increment lines for each end-of-line seen;
                // Decrement for \r\n
                while (is && ((c1 = is.get_undelim ())
                              != std::istream::traits_type::eof ())
                       && (((c1 == m_eol1 || c1 == m_eol2) && ++m_lines)
                           || isspace (c1) || is_delim (c1)))
                  {
                    if (prev == m_eol1 && m_eol1 != m_eol2 && c1 == m_eol2)
                      m_lines--;
                    prev = c1;
                  }
                if (c1 != std::istream::traits_type::eof ())
                  is.putback (c1);
              }
          }
      }
    else                                  // multi-character delimiter
      {
        int first_match;

        if (c1 == m_eol1 || c1 == m_eol2
            || (-1 != (first_match = lookahead (is, m_delim_list, m_delim_len))))
          {
            if (c1 == m_eol1)
              {
                is.get_undelim ();
                if (is.peek_undelim () == m_eol2)
                  is.get_undelim ();
              }
            else if (c1 == m_eol2)
              {
                is.get_undelim ();
              }

            if (multiple_delims_as_one)
              {
                int prev = -1;
                // skip multiple delims.
                // Increment lines for each end-of-line seen;
                // decrement for \r\n.
                while (is && ((c1 = skip_whitespace (is))
                              != std::istream::traits_type::eof ())
                       && (((c1 == m_eol1 || c1 == m_eol2) && ++m_lines)
                           || -1 != lookahead (is, m_delim_list, m_delim_len)))
                  {
                    if (prev == m_eol1 && m_eol1 != m_eol2 && c1 == m_eol2)
                      m_lines--;
                    prev = c1;
                  }
              }
          }
      }

    return c1;
  }

  // Read in as much of the input as coincides with the literal in the
  // format string.  Return "true" if the entire literal is matched, else
  // false (and set failbit).

  bool
  textscan::match_literal (delimited_stream& is,
                           const textscan_format_elt& fmt)
  {
    // "false" -> treat EOL as normal space
    // since a delimiter at the start of a line is a mismatch, not empty field
    skip_whitespace (is, false);

    for (unsigned int i = 0; i < fmt.width; i++)
      {
        int ch = is.get_undelim ();
        if (ch != fmt.text[i])
          {
            if (ch != std::istream::traits_type::eof ())
              is.putback (ch);
            is.setstate (std::ios::failbit);
            return false;
          }
      }
    return true;
  }

  void
  base_stream::error (const std::string& msg)
  {
    m_fail = true;
    m_errmsg = msg;
  }

  void
  base_stream::error (const std::string& who, const std::string& msg)
  {
    m_fail = true;
    m_errmsg = who + ": " + msg;
  }

  void
  base_stream::clear (void)
  {
    m_fail = false;
    m_errmsg = "";
  }

  void
  base_stream::clearerr (void)
  {
    std::istream *is = input_stream ();
    std::ostream *os = preferred_output_stream ();

    if (is)
      is->clear ();

    if (os)
      os->clear ();
  }

  // Functions that are defined for all input streams (input streams
  // are those that define is).

  std::string
  base_stream::do_gets (octave_idx_type max_len, bool& err,
                        bool strip_newline, const std::string& who)
  {
    interpreter& interp = __get_interpreter__ ();

    if (interp.interactive () && file_number () == 0)
      ::error ("%s: unable to read from stdin while running interactively",
               who.c_str ());

    std::string retval;

    err = false;

    std::istream *isp = input_stream ();

    if (! isp)
      {
        err = true;
        invalid_operation (who, "reading");
      }
    else
      {
        std::istream& is = *isp;

        std::ostringstream buf;

        int c = 0;
        int char_count = 0;

        if (max_len != 0)
          {
            while (is && (c = is.get ()) != std::istream::traits_type::eof ())
              {
                char_count++;

                // Handle CRLF, CR, or LF as line ending.
                if (c == '\r')
                  {
                    if (! strip_newline)
                      buf << static_cast<char> (c);

                    c = is.get ();

                    if (c != std::istream::traits_type::eof ())
                      {
                        if (c == '\n')
                          {
                            char_count++;

                            if (! strip_newline)
                              buf << static_cast<char> (c);
                          }
                        else
                          is.putback (c);
                      }

                    break;
                  }
                else if (c == '\n')
                  {
                    if (! strip_newline)
                      buf << static_cast<char> (c);

                    break;
                  }
                else
                  buf << static_cast<char> (c);

                if (max_len > 0 && char_count == max_len)
                  break;
              }
          }

        if (! is.eof () && char_count > 0)
          {
            // GAGME.  Matlab seems to check for EOF even if the last character
            // in a file is a newline character.  This is NOT what the
            // corresponding C-library functions do.
            int disgusting_compatibility_hack = is.get ();
            if (! is.eof ())
              is.putback (disgusting_compatibility_hack);
          }

        if (is.good () || (is.eof () && char_count > 0))
          {
            retval = buf.str ();
            if (encoding ().compare ("utf-8"))
              retval = string::u8_from_encoding (who, retval, encoding ());
          }
        else
          {
            err = true;

            if (is.eof () && char_count == 0)
              error (who, "at end of file");
            else
              error (who, "read error");
          }
      }

    return retval;
  }

  std::string
  base_stream::getl (octave_idx_type max_len, bool& err,
                     const std::string& who)
  {
    return do_gets (max_len, err, true, who);
  }

  std::string
  base_stream::gets (octave_idx_type max_len, bool& err,
                     const std::string& who)
  {
    return do_gets (max_len, err, false, who);
  }

  off_t
  base_stream::skipl (off_t num, bool& err, const std::string& who)
  {
    interpreter& interp = __get_interpreter__ ();

    if (interp.interactive () && file_number () == 0)
      ::error ("%s: unable to read from stdin while running interactively",
               who.c_str ());

    off_t cnt = -1;

    err = false;

    std::istream *isp = input_stream ();

    if (! isp)
      {
        err = true;
        invalid_operation (who, "reading");
      }
    else
      {
        std::istream& is = *isp;

        int c = 0;
        int lastc = -1;
        cnt = 0;

        while (is && (c = is.get ()) != std::istream::traits_type::eof ())
          {
            // Handle CRLF, CR, or LF as line ending.
            if (c == '\r' || (c == '\n' && lastc != '\r'))
              {
                if (++cnt == num)
                  break;
              }

            lastc = c;
          }

        // Maybe eat the following \n if \r was just met.
        if (c == '\r' && is.peek () == '\n')
          is.get ();

        if (is.bad ())
          {
            err = true;
            error (who, "read error");
          }

        if (err)
          cnt = -1;
      }

    return cnt;
  }

  template <typename T>
  static std::istream&
  octave_scan_1 (std::istream& is, const scanf_format_elt& fmt,
                 T *valptr)
  {
    T value = T ();

    switch (fmt.type)
      {
      case 'o':
        is >> std::oct >> value >> std::dec;
        break;

      case 'x':
      case 'X':
        is >> std::hex >> value >> std::dec;
        break;

      case 'i':
        {
          int c1 = std::istream::traits_type::eof ();

          while (is && (c1 = is.get ()) != std::istream::traits_type::eof ()
                 && isspace (c1))
            ; // skip whitespace

          if (c1 != std::istream::traits_type::eof ())
            {
              if (c1 == '0')
                {
                  int c2 = is.peek ();

                  if (c2 == 'x' || c2 == 'X')
                    {
                      is.ignore ();
                      if (std::isxdigit (is.peek ()))
                        is >> std::hex >> value >> std::dec;
                      else
                        value = 0;
                    }
                  else
                    {
                      if (c2 == '0' || c2 == '1' || c2 == '2'
                          || c2 == '3' || c2 == '4' || c2 == '5'
                          || c2 == '6' || c2 == '7')
                        is >> std::oct >> value >> std::dec;
                      else if (c2 == '8' || c2 == '9')
                        {
                          // FIXME: Would like to set error state on octave
                          // stream.  See bug #46493.  But only std::istream is
                          // input to fcn.
                          // error ("internal failure to match octal format");
                          value = 0;
                        }
                      else
                        value = 0;
                    }
                }
              else
                {
                  is.putback (c1);

                  is >> value;
                }
            }
        }
        break;

      default:
        is >> value;
        break;
      }

    // If conversion produces an integer that overflows, failbit is set but
    // value is non-zero.  We want to treat this case as success, so clear
    // failbit from the stream state to keep going.
    // FIXME: Maybe set error state on octave stream as above? Matlab does
    // *not* indicate an error message on overflow.
    if ((is.rdstate () & std::ios::failbit) && value != T ())
      is.clear (is.rdstate () & ~std::ios::failbit);

    // Only copy the converted value if the stream is in a state where we
    // want to continue reading.
    if (! (is.rdstate () & std::ios::failbit))
      *valptr = value;

    return is;
  }

  template <typename T>
  static std::istream&
  octave_scan (std::istream& is, const scanf_format_elt& fmt, T *valptr)
  {
    if (fmt.width)
      {
        // Limit input to fmt.width characters by reading into a
        // temporary stringstream buffer.
        std::string strbuf;

        auto orig_pos = is.tellg ();

        is.width (fmt.width);
        is >> strbuf;

        std::istringstream ss (strbuf);

        octave_scan_1 (ss, fmt, valptr);

        if (! ss.eof ())
          {
            // If fewer characters than width were used to read a number then
            // the original istream object positioning is incorrect.
            // Rather than attempt to update istream state and positioning,
            // just redo the '>>' operation with the correct width so that
            // all flags get set correctly.

            is.clear ();  // Clear EOF, FAILBIT, BADBIT
            is.seekg (orig_pos, is.beg);

            int chars_read = ss.tellg ();
            if (chars_read > 0)
              {
                is.width (chars_read);
                is >> strbuf;
              }
          }

        // If pattern failed to match then propagate fail bit to 'is' stream.
        if (ss.fail ())
          is.setstate (std::ios::failbit);

      }
    else
      octave_scan_1 (is, fmt, valptr);

    return is;
  }

  template <>
  std::istream&
  octave_scan<> (std::istream& is, const scanf_format_elt& fmt, double *valptr)
  {
    double& ref = *valptr;

    switch (fmt.type)
      {
      case 'e':
      case 'f':
      case 'g':
      case 'E':
      case 'G':
        {
          int c1 = std::istream::traits_type::eof ();

          while (is && (c1 = is.get ()) != std::istream::traits_type::eof ()
                 && isspace (c1))
            ; // skip whitespace

          if (c1 != std::istream::traits_type::eof ())
            {
              is.putback (c1);

              ref = read_value<double> (is);
            }
        }
        break;

      default:
        panic_impossible ();
        break;
      }

    return is;
  }

  template <typename T>
  static void
  do_scanf_conv (std::istream& is, const scanf_format_elt& fmt,
                 T valptr, Matrix& mval, double *data, octave_idx_type& idx,
                 octave_idx_type& conversion_count, octave_idx_type nr,
                 octave_idx_type max_size, bool discard)
  {
    octave_scan (is, fmt, valptr);

    if (! is)
      return;

    if (idx == max_size && ! discard)
      {
        max_size *= 2;

        if (nr > 0)
          mval.resize (nr, max_size / nr, 0.0);
        else
          mval.resize (max_size, 1, 0.0);

        data = mval.fortran_vec ();
      }

    if (! discard)
      {
        conversion_count++;
        data[idx++] = *(valptr);
      }
  }

  template void
  do_scanf_conv (std::istream&, const scanf_format_elt&, double *,
                 Matrix&, double *, octave_idx_type&, octave_idx_type&,
                 octave_idx_type, octave_idx_type, bool);

#define DO_WHITESPACE_CONVERSION()                                      \
  do                                                                    \
    {                                                                   \
      int c = std::istream::traits_type::eof ();                        \
                                                                        \
      while (is && (c = is.get ()) != std::istream::traits_type::eof () \
             && isspace (c))                                            \
        { /* skip whitespace */ }                                       \
                                                                        \
      if (c != std::istream::traits_type::eof ())                       \
        is.putback (c);                                                 \
    }                                                                   \
  while (0)

#define DO_LITERAL_CONVERSION()                                         \
  do                                                                    \
    {                                                                   \
      int c = std::istream::traits_type::eof ();                        \
                                                                        \
      int n = fmt.length ();                                            \
      int i = 0;                                                        \
                                                                        \
      while (i < n && is                                                \
             && (c = is.get ()) != std::istream::traits_type::eof ())   \
        {                                                               \
          if (c == static_cast<unsigned char> (fmt[i]))                 \
            {                                                           \
              i++;                                                      \
              continue;                                                 \
            }                                                           \
          else                                                          \
            {                                                           \
              is.putback (c);                                           \
              break;                                                    \
            }                                                           \
        }                                                               \
                                                                        \
      if (i != n)                                                       \
        is.setstate (std::ios::failbit);                                \
    }                                                                   \
  while (0)

#define DO_PCT_CONVERSION()                             \
  do                                                    \
    {                                                   \
      int c = is.get ();                                \
                                                        \
      if (c != std::istream::traits_type::eof ())       \
        {                                               \
          if (c != '%')                                 \
            {                                           \
              is.putback (c);                           \
              is.setstate (std::ios::failbit);          \
            }                                           \
        }                                               \
      else                                              \
        is.setstate (std::ios::failbit);                \
    }                                                   \
  while (0)

#define BEGIN_C_CONVERSION()                                            \
  is.unsetf (std::ios::skipws);                                         \
                                                                        \
  int width = (elt->width ? elt->width : 1);                            \
                                                                        \
  std::string tmp (width, '\0');                                        \
                                                                        \
  int c = std::istream::traits_type::eof ();                            \
  int n = 0;                                                            \
                                                                        \
  while (is && n < width                                                \
         && (c = is.get ()) != std::istream::traits_type::eof ())       \
    tmp[n++] = static_cast<char> (c);                                   \
                                                                        \
  if (c == std::istream::traits_type::eof ())                           \
    is.clear (is.rdstate () & (~std::ios::failbit));                    \
                                                                        \
  tmp.resize (n)

  // For a '%s' format, skip initial whitespace and then read until the
  // next whitespace character or until WIDTH characters have been read.
#define BEGIN_S_CONVERSION()                                            \
  int width = elt->width;                                               \
                                                                        \
  std::string tmp;                                                      \
                                                                        \
  do                                                                    \
    {                                                                   \
      if (width)                                                        \
        {                                                               \
          tmp = std::string (width, '\0');                              \
                                                                        \
          int c = std::istream::traits_type::eof ();                    \
                                                                        \
          int n = 0;                                                    \
                                                                        \
          while (is && (c = is.get ()) != std::istream::traits_type::eof ()) \
            {                                                           \
              if (! isspace (c))                                        \
                {                                                       \
                  tmp[n++] = static_cast<char> (c);                     \
                  break;                                                \
                }                                                       \
            }                                                           \
                                                                        \
          while (is && n < width                                        \
                 && (c = is.get ()) != std::istream::traits_type::eof ()) \
            {                                                           \
              if (isspace (c))                                          \
                {                                                       \
                  is.putback (c);                                       \
                  break;                                                \
                }                                                       \
              else                                                      \
                tmp[n++] = static_cast<char> (c);                       \
            }                                                           \
                                                                        \
          if (c == std::istream::traits_type::eof ())                   \
            is.clear (is.rdstate () & (~std::ios::failbit));            \
                                                                        \
          tmp.resize (n);                                               \
        }                                                               \
      else                                                              \
        {                                                               \
          is >> std::ws >> tmp;                                         \
        }                                                               \
    }                                                                   \
  while (0)

  // This format must match a nonempty sequence of characters.
#define BEGIN_CHAR_CLASS_CONVERSION()                                   \
  int width = (elt->width ? elt->width                                  \
                          : std::numeric_limits<int>::max ());          \
                                                                        \
  std::string tmp;                                                      \
                                                                        \
  do                                                                    \
    {                                                                   \
      std::ostringstream buf;                                           \
                                                                        \
      std::string char_class = elt->char_class;                         \
                                                                        \
      int c = std::istream::traits_type::eof ();                        \
                                                                        \
      if (elt->type == '[')                                             \
        {                                                               \
          int chars_read = 0;                                           \
          while (is && chars_read++ < width                             \
                 && (c = is.get ()) != std::istream::traits_type::eof ()) \
            {                                                           \
              if (char_class.find (c) != std::string::npos)             \
                buf << static_cast<char> (c);                           \
              else                                                      \
                {                                                       \
                  is.putback (c);                                       \
                  break;                                                \
                }                                                       \
            }                                                           \
        }                                                               \
      else                                                              \
        {                                                               \
          int chars_read = 0;                                           \
          while (is && chars_read++ < width                             \
                 && (c = is.get ()) != std::istream::traits_type::eof ()) \
            {                                                           \
              if (char_class.find (c) == std::string::npos)             \
                buf << static_cast<char> (c);                           \
              else                                                      \
                {                                                       \
                  is.putback (c);                                       \
                  break;                                                \
                }                                                       \
            }                                                           \
        }                                                               \
                                                                        \
      tmp = buf.str ();                                                 \
                                                                        \
      if (tmp.empty ())                                                 \
        is.setstate (std::ios::failbit);                                \
      else if (c == std::istream::traits_type::eof ())                  \
        is.clear (is.rdstate () & (~std::ios::failbit));                \
                                                                        \
    }                                                                   \
  while (0)

#define FINISH_CHARACTER_CONVERSION()                                   \
  do                                                                    \
    {                                                                   \
      if (encoding ().compare ("utf-8"))                                \
        tmp = string::u8_from_encoding (who, tmp, encoding ());         \
      width = tmp.length ();                                            \
                                                                        \
      if (is && width > 0)                                              \
        {                                                               \
          int i = 0;                                                    \
                                                                        \
          if (! discard)                                                \
            {                                                           \
              conversion_count++;                                       \
                                                                        \
              while (i < width)                                         \
                {                                                       \
                  if (data_index == max_size)                           \
                    {                                                   \
                      max_size *= 2;                                    \
                                                                        \
                      if (all_char_conv)                                \
                        {                                               \
                          if (one_elt_size_spec)                        \
                            mval.resize (1, max_size, 0.0);             \
                          else if (nr > 0)                              \
                            mval.resize (nr, max_size / nr, 0.0);       \
                          else                                          \
                            panic_impossible ();                        \
                        }                                               \
                      else if (nr > 0)                                  \
                        mval.resize (nr, max_size / nr, 0.0);           \
                      else                                              \
                        mval.resize (max_size, 1, 0.0);                 \
                                                                        \
                      data = mval.fortran_vec ();                       \
                    }                                                   \
                                                                        \
                  data[data_index++] = static_cast<unsigned char>       \
                                                  (tmp[i++]);           \
                }                                                       \
            }                                                           \
        }                                                               \
    }                                                                   \
  while (0)

  octave_value
  base_stream::do_scanf (scanf_format_list& fmt_list,
                         octave_idx_type nr, octave_idx_type nc,
                         bool one_elt_size_spec,
                         octave_idx_type& conversion_count,
                         const std::string& who)
  {
    interpreter& interp = __get_interpreter__ ();

    if (interp.interactive () && file_number () == 0)
      ::error ("%s: unable to read from stdin while running interactively",
               who.c_str ());

    octave_value retval = Matrix ();

    conversion_count = 0;

    octave_idx_type m_nconv = fmt_list.num_conversions ();

    octave_idx_type data_index = 0;

    if (nr == 0 || nc == 0)
      {
        if (one_elt_size_spec)
          nc = 0;

        return Matrix (nr, nc, 0.0);
      }

    std::istream *isp = input_stream ();

    bool all_char_conv = fmt_list.all_character_conversions ();

    Matrix mval;
    octave_idx_type max_size = 0;
    octave_idx_type max_conv = 0;

    octave_idx_type final_nr = 0;
    octave_idx_type final_nc = 0;

    if (all_char_conv)
      {
        // Any of these could be resized later (if we have %s conversions,
        // we may read more than one element for each conversion).
        if (one_elt_size_spec)
          {
            max_size = 512;
            mval.resize (1, max_size, 0.0);

            if (nr > 0)
              max_conv = nr;
          }
        else if (nr > 0)
          {
            if (nc > 0)
              {
                mval.resize (nr, nc, 0.0);
                max_size = max_conv = nr * nc;
              }
            else
              {
                mval.resize (nr, 32, 0.0);
                max_size = nr * 32;
              }
          }
        else
          panic_impossible ();
      }
    else if (nr > 0)
      {
        if (nc > 0)
          {
            // Will not resize later.
            mval.resize (nr, nc, 0.0);
            max_size = nr * nc;
            max_conv = max_size;
          }
        else
          {
            // Maybe resize later.
            mval.resize (nr, 32, 0.0);
            max_size = nr * 32;
          }
      }
    else
      {
        // Maybe resize later.
        mval.resize (32, 1, 0.0);
        max_size = 32;
      }

    double *data = mval.fortran_vec ();

    if (isp)
      {
        std::istream& is = *isp;

        const scanf_format_elt *elt = fmt_list.first ();

        std::ios::fmtflags flags = is.flags ();

        octave_idx_type trips = 0;

        octave_idx_type num_fmt_elts = fmt_list.length ();

        for (;;)
          {
            octave_quit ();

            if (elt)
              {
                if (elt->type == scanf_format_elt::null
                    || (! (elt->type == scanf_format_elt::whitespace_conversion
                           || elt->type == scanf_format_elt::literal_conversion
                           || elt->type == '%')
                        && max_conv > 0 && conversion_count == max_conv))
                  {
                    // We are done, either because we have reached the end of
                    // the format string and are not cycling through the format
                    // again or because we've converted all the values that
                    // have been requested and the next format element is a
                    // conversion.  Determine final array size and exit.
                    if (all_char_conv && one_elt_size_spec)
                      {
                        final_nr = 1;
                        final_nc = data_index;
                      }
                    else
                      {
                        final_nr = nr;
                        final_nc = (data_index - 1) / nr + 1;
                      }

                    break;
                  }
                else if (data_index == max_size)
                  {
                    max_size *= 2;

                    if (all_char_conv)
                      {
                        if (one_elt_size_spec)
                          mval.resize (1, max_size, 0.0);
                        else if (nr > 0)
                          mval.resize (nr, max_size / nr, 0.0);
                        else
                          panic_impossible ();
                      }
                    else if (nr > 0)
                      mval.resize (nr, max_size / nr, 0.0);
                    else
                      mval.resize (max_size, 1, 0.0);

                    data = mval.fortran_vec ();
                  }

                std::string fmt = elt->text;

                bool discard = elt->discard;

                switch (elt->type)
                  {
                  case scanf_format_elt::whitespace_conversion:
                    DO_WHITESPACE_CONVERSION ();
                    break;

                  case scanf_format_elt::literal_conversion:
                    DO_LITERAL_CONVERSION ();
                    break;

                  case '%':
                    DO_PCT_CONVERSION ();
                    break;

                  case 'd': case 'i':
                    {
                      switch (elt->modifier)
                        {
                        case 'h':
                          {
                            int16_t tmp;
                            do_scanf_conv (is, *elt, &tmp, mval, data,
                                           data_index, conversion_count,
                                           nr, max_size, discard);
                          }
                          break;

                        case 'l':
                          {
                            int64_t tmp;
                            do_scanf_conv (is, *elt, &tmp, mval, data,
                                           data_index, conversion_count,
                                           nr, max_size, discard);
                          }
                          break;

                        default:
                          {
                            int32_t tmp;
                            do_scanf_conv (is, *elt, &tmp, mval, data,
                                           data_index, conversion_count,
                                           nr, max_size, discard);
                          }
                          break;
                        }
                    }
                    break;

                  case 'o': case 'u': case 'x': case 'X':
                    {
                      switch (elt->modifier)
                        {
                        case 'h':
                          {
                            uint16_t tmp;
                            do_scanf_conv (is, *elt, &tmp, mval, data,
                                           data_index, conversion_count,
                                           nr, max_size, discard);
                          }
                          break;

                        case 'l':
                          {
                            uint64_t tmp;
                            do_scanf_conv (is, *elt, &tmp, mval, data,
                                           data_index, conversion_count,
                                           nr, max_size, discard);
                          }
                          break;

                        default:
                          {
                            uint32_t tmp;
                            do_scanf_conv (is, *elt, &tmp, mval, data,
                                           data_index, conversion_count,
                                           nr, max_size, discard);
                          }
                          break;
                        }
                    }
                    break;

                  case 'e': case 'f': case 'g':
                  case 'E': case 'G':
                    {
                      double tmp;

                      do_scanf_conv (is, *elt, &tmp, mval, data,
                                     data_index, conversion_count,
                                     nr, max_size, discard);
                    }
                    break;

                  case 'c':
                    {
                      BEGIN_C_CONVERSION ();

                      FINISH_CHARACTER_CONVERSION ();

                      is.setf (flags);
                    }
                    break;

                  case 's':
                    {
                      BEGIN_S_CONVERSION ();

                      FINISH_CHARACTER_CONVERSION ();
                    }
                    break;

                  case '[': case '^':
                    {
                      BEGIN_CHAR_CLASS_CONVERSION ();

                      FINISH_CHARACTER_CONVERSION ();
                    }
                    break;

                  case 'p':
                    error (who, "unsupported format specifier");
                    break;

                  default:
                    error (who, "internal format error");
                    break;
                  }

                if (! ok ())
                  {
                    break;
                  }
                else if (is.eof () || ! is)
                  {
                    if (all_char_conv)
                      {
                        if (one_elt_size_spec)
                          {
                            final_nr = 1;
                            final_nc = data_index;
                          }
                        else if (data_index > nr)
                          {
                            final_nr = nr;
                            final_nc = (data_index - 1) / nr + 1;
                          }
                        else
                          {
                            final_nr = data_index;
                            final_nc = 1;
                          }
                      }
                    else if (nr > 0)
                      {
                        if (data_index > nr)
                          {
                            final_nr = nr;
                            final_nc = (data_index - 1) / nr + 1;
                          }
                        else
                          {
                            final_nr = data_index;
                            final_nc = 1;
                          }
                      }
                    else
                      {
                        final_nr = data_index;
                        final_nc = 1;
                      }

                    // If it looks like we have a matching failure, then
                    // reset the failbit in the stream state.
                    if (is.rdstate () & std::ios::failbit)
                      {
                        error (who, "format failed to match");
                        is.clear (is.rdstate () & (~std::ios::failbit));
                      }

                    // FIXME: is this the right thing to do?
                    if (interp.interactive ()
                        && ! application::forced_interactive ()
                        && name () == "stdin")
                      {
                        is.clear ();

                        // Skip to end of line.
                        bool err;
                        do_gets (-1, err, false, who);
                      }

                    break;
                  }
              }
            else
              {
                error (who, "internal format error");
                break;
              }

            if (m_nconv == 0 && ++trips == num_fmt_elts)
              {
                if (all_char_conv && one_elt_size_spec)
                  {
                    final_nr = 1;
                    final_nc = data_index;
                  }
                else
                  {
                    final_nr = nr;
                    final_nc = (data_index - 1) / nr + 1;
                  }

                break;
              }
            else
              {
                // Cycle through the format list more than once if we have some
                // conversions to make and we haven't reached the limit on the
                // number of values to convert (possibly because there is no
                // specified limit).
                elt = fmt_list.next (m_nconv > 0
                                     && (max_conv == 0
                                         || conversion_count < max_conv));
              }
          }
      }

    mval.resize (final_nr, final_nc, 0.0);

    retval = mval;

    if (all_char_conv)
      retval = retval.convert_to_str (false, true);

    return retval;
  }

  octave_value
  base_stream::scanf (const std::string& fmt, const Array<double>& size,
                      octave_idx_type& conversion_count,
                      const std::string& who)
  {
    octave_value retval = Matrix ();

    conversion_count = 0;

    std::istream *isp = input_stream ();

    if (! isp)
      invalid_operation (who, "reading");
    else
      {
        scanf_format_list fmt_list (fmt);

        if (fmt_list.num_conversions () == -1)
          ::error ("%s: invalid format specified", who.c_str ());

        octave_idx_type nr = -1;
        octave_idx_type nc = -1;

        bool one_elt_size_spec;

        get_size (size, nr, nc, one_elt_size_spec, who);

        retval = do_scanf (fmt_list, nr, nc, one_elt_size_spec,
                           conversion_count, who);
      }

    return retval;
  }

  bool
  base_stream::do_oscanf (const scanf_format_elt *elt,
                          octave_value& retval, const std::string& who)
  {
    std::istream *isp = input_stream ();

    if (! isp)
      return false;

    bool quit = false;

    std::istream& is = *isp;

    std::ios::fmtflags flags = is.flags ();

    if (elt)
      {
        std::string fmt = elt->text;

        bool discard = elt->discard;

        switch (elt->type)
          {
          case scanf_format_elt::whitespace_conversion:
            DO_WHITESPACE_CONVERSION ();
            break;

          case scanf_format_elt::literal_conversion:
            DO_LITERAL_CONVERSION ();
            break;

          case '%':
            {
              DO_PCT_CONVERSION ();

              if (! is)
                quit = true;
            }
            break;

          case 'd': case 'i':
            {
              switch (elt->modifier)
                {
                case 'h':
                  {
                    int16_t tmp;
                    if (octave_scan (is, *elt, &tmp))
                      {
                        if (! discard)
                          retval = tmp;
                      }
                    else
                      quit = true;
                  }
                  break;

                case 'l':
                  {
                    int64_t tmp;
                    if (octave_scan (is, *elt, &tmp))
                      {
                        if (! discard)
                          retval = tmp;
                      }
                    else
                      quit = true;
                  }
                  break;

                default:
                  {
                    int32_t tmp;
                    if (octave_scan (is, *elt, &tmp))
                      {
                        if (! discard)
                          retval = tmp;
                      }
                    else
                      quit = true;
                  }
                  break;
                }
            }
            break;

          case 'o': case 'u': case 'x': case 'X':
            {
              switch (elt->modifier)
                {
                case 'h':
                  {
                    uint16_t tmp;
                    if (octave_scan (is, *elt, &tmp))
                      {
                        if (! discard)
                          retval = tmp;
                      }
                    else
                      quit = true;
                  }
                  break;

                case 'l':
                  {
                    uint64_t tmp;
                    if (octave_scan (is, *elt, &tmp))
                      {
                        if (! discard)
                          retval = tmp;
                      }
                    else
                      quit = true;
                  }
                  break;

                default:
                  {
                    uint32_t tmp;
                    if (octave_scan (is, *elt, &tmp))
                      {
                        if (! discard)
                          retval = tmp;
                      }
                    else
                      quit = true;
                  }
                  break;
                }
            }
            break;

          case 'e': case 'f': case 'g':
          case 'E': case 'G':
            {
              double tmp;

              if (octave_scan (is, *elt, &tmp))
                {
                  if (! discard)
                    retval = tmp;
                }
              else
                quit = true;
            }
            break;

          case 'c':
            {
              BEGIN_C_CONVERSION ();

              if (! discard)
                retval = tmp;

              if (! is)
                quit = true;

              is.setf (flags);
            }
            break;

          case 's':
            {
              BEGIN_S_CONVERSION ();

              if (! discard)
                retval = tmp;

              if (! is)
                quit = true;
            }
            break;

          case '[':
          case '^':
            {
              BEGIN_CHAR_CLASS_CONVERSION ();

              if (! discard)
                retval = tmp;

              if (! is)
                quit = true;
            }
            break;

          case 'p':
            error (who, "unsupported format specifier");
            break;

          default:
            error (who, "internal format error");
            break;
          }
      }

    if (ok () && is.fail ())
      {
        error ("%s: read error", who.c_str ());

        // FIXME: is this the right thing to do?

        interpreter& interp = __get_interpreter__ ();

        if (interp.interactive () && ! application::forced_interactive ()
            && name () == "stdin")
          {
            // Skip to end of line.
            bool err;
            do_gets (-1, err, false, who);
          }
      }

    return quit;
  }

  octave_value_list
  base_stream::oscanf (const std::string& fmt, const std::string& who)
  {
    octave_value_list retval;

    std::istream *isp = input_stream ();

    if (! isp)
      invalid_operation (who, "reading");
    else
      {
        std::istream& is = *isp;

        scanf_format_list fmt_list (fmt);

        octave_idx_type m_nconv = fmt_list.num_conversions ();

        if (m_nconv == -1)
          ::error ("%s: invalid format specified", who.c_str ());

        is.clear ();

        octave_idx_type len = fmt_list.length ();

        retval.resize (m_nconv+2, Matrix ());

        const scanf_format_elt *elt = fmt_list.first ();

        int num_values = 0;

        bool quit = false;

        for (octave_idx_type i = 0; i < len; i++)
          {
            octave_value tmp;

            quit = do_oscanf (elt, tmp, who);

            if (quit)
              break;
            else
              {
                if (tmp.is_defined ())
                  retval(num_values++) = tmp;

                if (! ok ())
                  break;

                elt = fmt_list.next (m_nconv > 0);
              }
          }

        retval(m_nconv) = num_values;

        int err_num;
        retval(m_nconv+1) = error (false, err_num);

        if (! quit)
          {
            // Pick up any trailing stuff.
            if (ok () && len > m_nconv)
              {
                octave_value tmp;

                elt = fmt_list.next ();

                do_oscanf (elt, tmp, who);
              }
          }
      }

    return retval;
  }

  octave_value
  base_stream::do_textscan (const std::string& fmt,
                            octave_idx_type ntimes,
                            const octave_value_list& options,
                            const std::string& who,
                            octave_idx_type& read_count)
  {
    interpreter& interp = __get_interpreter__ ();

    if (interp.interactive () && file_number () == 0)
      ::error ("%s: unable to read from stdin while running interactively",
               who.c_str ());

    octave_value retval = Cell (dim_vector (1, 1), Matrix (0, 1));

    std::istream *isp = input_stream ();

    if (! isp)
      invalid_operation (who, "reading");
    else
      {
        textscan scanner (who, encoding ());

        retval = scanner.scan (*isp, fmt, ntimes, options, read_count);
      }

    return retval;
  }

  // Functions that are defined for all output streams
  // (output streams are those that define os).

  int
  base_stream::flush (void)
  {
    int retval = -1;

    std::ostream *os = preferred_output_stream ();

    if (! os)
      invalid_operation ("fflush", "writing");
    else
      {
        os->flush ();

        if (os->good ())
          retval = 0;
      }

    return retval;
  }

  class
  printf_value_cache
  {
  public:

    enum state { ok, conversion_error };

    printf_value_cache (const octave_value_list& args, const std::string& who)
      : m_values (args), m_val_idx (0), m_elt_idx (0),
        m_n_vals (m_values.length ()), m_n_elts (0), m_have_data (false),
        m_curr_state (ok)
    {
      for (octave_idx_type i = 0; i < m_values.length (); i++)
        {
          octave_value val = m_values(i);

          if (val.isstruct () || val.iscell () || val.isobject ())
            err_wrong_type_arg (who, val);
        }
    }

    // No copying!

    printf_value_cache (const printf_value_cache&) = delete;

    printf_value_cache& operator = (const printf_value_cache&) = delete;

    ~printf_value_cache (void) = default;

    // Get the current value as a double and advance the internal pointer.
    octave_value get_next_value (char type = 0);

    // Get the current value as an int and advance the internal
    // pointer.  Value before conversion to int must be >= 0 and less
    // than std::numeric_limits<int>::max ().

    int int_value (void);

    operator bool () const { return (m_curr_state == ok); }

    bool exhausted (void) { return (m_val_idx >= m_n_vals); }

  private:

    // Must create value cache with values!
    printf_value_cache (void);

    //--------

    const octave_value_list m_values;
    octave_idx_type m_val_idx;
    octave_idx_type m_elt_idx;
    octave_idx_type m_n_vals;
    octave_idx_type m_n_elts;
    bool m_have_data;
    octave_value m_curr_val;
    state m_curr_state;
  };

  octave_value
  printf_value_cache::get_next_value (char type)
  {
    octave_value retval;

    if (exhausted ())
      m_curr_state = conversion_error;

    while (! exhausted ())
      {
        if (! m_have_data)
          {
            m_curr_val = m_values (m_val_idx);

            m_elt_idx = 0;
            m_n_elts = m_curr_val.numel ();
            m_have_data = true;
          }

        if (m_elt_idx < m_n_elts)
          {
            if (type == 's')
              {
                if (m_curr_val.is_string ())
                  {
                    dim_vector dv (1, m_curr_val.numel ());
                    octave_value tmp = m_curr_val.reshape (dv);

                    std::string sval = tmp.string_value ();

                    retval = sval.substr (m_elt_idx);

                    // We've consumed the rest of the value.
                    m_elt_idx = m_n_elts;
                  }
                else
                  {
                    // Convert to character string while values are
                    // integers in the range [0 : char max]
                    const NDArray val = m_curr_val.array_value ();

                    octave_idx_type idx = m_elt_idx;

                    for (; idx < m_n_elts; idx++)
                      {
                        double dval = val(idx);

                        if (math::x_nint (dval) != dval
                            || dval < 0 || dval > 255)
                          break;
                      }

                    octave_idx_type n = idx - m_elt_idx;

                    if (n > 0)
                      {
                        std::string sval (n, '\0');

                        for (octave_idx_type i = 0; i < n; i++)
                          sval[i] = val(m_elt_idx++);

                        retval = sval;
                      }
                    else
                      retval = m_curr_val.fast_elem_extract (m_elt_idx++);
                  }
              }
            else
              {
                retval = m_curr_val.fast_elem_extract (m_elt_idx++);

                if (type == 'c' && ! retval.is_string ())
                  {
                    double dval = retval.double_value ();

                    if (math::x_nint (dval) == dval && dval >= 0 && dval < 256)
                      retval = static_cast<char> (dval);
                  }
              }

            if (m_elt_idx >= m_n_elts)
              {
                m_elt_idx = 0;
                m_val_idx++;
                m_have_data = false;
              }

            break;
          }
        else
          {
            m_val_idx++;
            m_have_data = false;

            if (m_n_elts == 0)
              {
                if (m_elt_idx == 0)
                  {
                    if (type == 's' || type == 'c')
                      retval = "";
                    else
                      retval = Matrix ();

                    break;
                  }

                if (exhausted ())
                  m_curr_state = conversion_error;
              }
          }
      }

    return retval;
  }

  int
  printf_value_cache::int_value (void)
  {
    octave_value val = get_next_value ();

    double dval = val.double_value (true);

    if (dval < 0 || dval > std::numeric_limits<int>::max ()
        || math::x_nint (dval) != dval)
      {
        m_curr_state = conversion_error;
        return -1;
      }

    return math::nint (dval);
  }

  // Ugh again and again.

  template <typename T>
  static int
  do_printf_conv (std::ostream& os, const char *fmt, int nsa, int sa_1,
                  int sa_2, T arg, const std::string& who)
  {
    int retval = 0;

    switch (nsa)
      {
      case 2:
        retval = format (os, fmt, sa_1, sa_2, arg);
        break;

      case 1:
        retval = format (os, fmt, sa_1, arg);
        break;

      case 0:
        retval = format (os, fmt, arg);
        break;

      default:
        ::error ("%s: internal error handling format", who.c_str ());
        break;
      }

    return retval;
  }

  static std::size_t
  do_printf_string (std::ostream& os, const printf_format_elt *elt,
                    int nsa, int sa_1, int sa_2, const std::string& arg,
                    const std::string& who)
  {
    if (nsa > 2)
      ::error ("%s: internal error handling format", who.c_str ());

    std::string flags = elt->flags;

    bool left = flags.find ('-') != std::string::npos;

    std::size_t len = arg.length ();

    std::size_t prec = (nsa > 1 ? sa_2 : (elt->prec == -1 ? len : elt->prec));

    std::string print_str = prec < arg.length () ? arg.substr (0, prec) : arg;

    std::size_t fw = (nsa > 0 ? sa_1 : (elt->fw == -1 ? len : elt->fw));

    os << std::setw (fw) << (left ? std::left : std::right) << print_str;

    return len > fw ? len : fw;
  }

  static bool
  is_nan_or_inf (const octave_value& val)
  {
    octave_value ov_isnan = val.isnan ();
    octave_value ov_isinf = val.isinf ();

    return (ov_isnan.is_true () || ov_isinf.is_true ());
  }

  static bool
  ok_for_signed_int_conv (const octave_value& val)
  {
    uint64_t limit = std::numeric_limits<int64_t>::max ();

    if (val.is_string ())
      return true;
    else if (val.isinteger ())
      {
        if (val.is_uint64_type ())
          {
            octave_uint64 ival = val.uint64_scalar_value ();

            if (ival.value () <= limit)
              return true;
          }
        else
          return true;
      }
    else
      {
        double dval = val.double_value (true);

        if (dval == math::fix (dval) && dval <= limit)
          return true;
      }

    return false;
  }

  static bool
  ok_for_unsigned_int_conv (const octave_value& val)
  {
    if (val.is_string ())
      return true;
    else if (val.isinteger ())
      {
        // Easier than dispatching here...

        octave_value ov_is_ge_zero
          = binary_op (octave_value::op_ge, val, octave_value (0.0));

        return ov_is_ge_zero.is_true ();
      }
    else
      {
        double dval = val.double_value (true);

        uint64_t limit = std::numeric_limits<uint64_t>::max ();

        if (dval == math::fix (dval) && dval >= 0 && dval <= limit)
          return true;
      }

    return false;
  }

  static std::string
  switch_to_g_format (const printf_format_elt *elt)
  {
    std::string tfmt = elt->text;

    tfmt.replace (tfmt.rfind (elt->type), 1, "g");

    return tfmt;
  }

  int
  base_stream::do_numeric_printf_conv (std::ostream& os,
                                       const printf_format_elt *elt,
                                       int nsa, int sa_1, int sa_2,
                                       const octave_value& val,
                                       const std::string& who)
  {
    int retval = 0;

    std::string tfmt = elt->text;

    if (is_nan_or_inf (val))
      {
        double dval = val.double_value ();

        std::string::size_type i1, i2;

        tfmt.replace ((i1 = tfmt.rfind (elt->type)), 1, 1, 's');

        if ((i2 = tfmt.rfind ('.')) != std::string::npos && i2 < i1)
          {
            tfmt.erase (i2, i1-i2);
            if (elt->prec == -2)
              nsa--;
          }

        const char *tval;
        if (lo_ieee_isinf (dval))
          {
            if (elt->flags.find ('+') != std::string::npos)
              tval = (dval < 0 ? "-Inf" : "+Inf");
            else
              tval = (dval < 0 ? "-Inf" : "Inf");
          }
        else
          {
            if (elt->flags.find ('+') != std::string::npos)
              tval = (lo_ieee_is_NA (dval) ? "+NA" : "+NaN");
            else
              tval = (lo_ieee_is_NA (dval) ? "NA" : "NaN");
          }

        retval += do_printf_conv (os, tfmt.c_str (), nsa, sa_1, sa_2, tval,
                                  who);
      }
    else
      {
        static std::string llmod
          = (sizeof (long) == sizeof (int64_t) ? "l" : "ll");

        char type = elt->type;

        switch (type)
          {
          case 'd': case 'i': case 'c':
            if (ok_for_signed_int_conv (val))
              {
                octave_int64 tval = val.int64_scalar_value ();

                // Insert "long" modifier.
                tfmt.replace (tfmt.rfind (type), 1, llmod + type);

                retval += do_printf_conv (os, tfmt.c_str (), nsa, sa_1, sa_2,
                                          tval.value (), who);
              }
            else
              {
                tfmt = switch_to_g_format (elt);

                double dval = val.double_value (true);

                retval += do_printf_conv (os, tfmt.c_str (), nsa, sa_1, sa_2,
                                          dval, who);
              }
            break;

          case 'o': case 'x': case 'X': case 'u':
            if (ok_for_unsigned_int_conv (val))
              {
                octave_uint64 tval = val.uint64_scalar_value ();

                // Insert "long" modifier.
                tfmt.replace (tfmt.rfind (type), 1, llmod + type);

                retval += do_printf_conv (os, tfmt.c_str (), nsa, sa_1, sa_2,
                                          tval.value (), who);
              }
            else
              {
                tfmt = switch_to_g_format (elt);

                double dval = val.double_value (true);

                retval += do_printf_conv (os, tfmt.c_str (), nsa, sa_1, sa_2,
                                          dval, who);
              }
            break;

          case 'f': case 'e': case 'E':
          case 'g': case 'G':
            {
              double dval = val.double_value (true);

              retval += do_printf_conv (os, tfmt.c_str (), nsa, sa_1, sa_2,
                                        dval, who);
            }
            break;

          default:
            // Note: error is member fcn from base_stream, not ::error.
            // This error does not halt execution so "return ..." must exist.
            error (who, "invalid format specifier");
            return -1;
            break;
          }
      }

    return retval;
  }

  void
  base_stream::field_width_error (const std::string& who) const
  {
    ::error ("%s: invalid field width, must be integer >= 0 and <= INT_MAX",
             who.c_str ());
  }

  int
  base_stream::do_printf (printf_format_list& fmt_list,
                          const octave_value_list& args,
                          const std::string& who)
  {
    int retval = 0;

    octave_idx_type m_nconv = fmt_list.num_conversions ();

    std::ostream *osp = preferred_output_stream ();

    if (! osp)
      invalid_operation (who, "writing");
    else
      {
        std::ostream& os = *osp;

        preserve_stream_state stream_state (os);

        const printf_format_elt *elt = fmt_list.first ();

        printf_value_cache val_cache (args, who);

        for (;;)
          {
            octave_quit ();

            if (! elt)
              ::error ("%s: internal error handling format", who.c_str ());

            // NSA is the number of 'star' args to convert.
            int nsa = (elt->fw == -2) + (elt->prec == -2);

            int sa_1 = 0;
            int sa_2 = 0;

            if (nsa > 0)
              {
                sa_1 = val_cache.int_value ();

                if (! val_cache)
                  {
                    field_width_error (who);
                    break;
                  }
                else
                  {
                    if (nsa > 1)
                      {
                        sa_2 = val_cache.int_value ();

                        if (! val_cache)
                          {
                            field_width_error (who);
                            break;
                          }
                      }
                  }
              }

            if (elt->type == '%')
              {
                os << '%';
                retval++;
              }
            else if (elt->args == 0 && ! elt->text.empty ())
              {
                os << elt->text;
                retval += (elt->text.length ());
              }
            else if (elt->type == 's' || elt->type == 'c')
              {
                octave_value val = val_cache.get_next_value (elt->type);

                if (val_cache)
                  {
                    if (val.is_string ())
                      {
                        std::string sval = val.string_value ();

                        retval += do_printf_string (os, elt, nsa, sa_1,
                                                    sa_2, sval, who);
                      }
                    else
                      retval += do_numeric_printf_conv (os, elt, nsa, sa_1,
                                                        sa_2, val, who);
                  }
                else
                  break;
              }
            else
              {
                octave_value val = val_cache.get_next_value ();

                if (val_cache)
                  {
                    if (! val.isempty ())
                      retval += do_numeric_printf_conv (os, elt, nsa, sa_1,
                                                        sa_2, val, who);
                  }
                else
                  break;
              }

            if (! os)
              {
                error (who, "write error");
                break;
              }

            elt = fmt_list.next (m_nconv > 0 && ! val_cache.exhausted ());

            if (! elt || (val_cache.exhausted () && elt->args > 0))
              break;
          }
      }

    return retval;
  }

  int
  base_stream::printf (const std::string& fmt,
                       const octave_value_list& args,
                       const std::string& who)
  {
    printf_format_list fmt_list (fmt);

    if (fmt_list.num_conversions () == -1)
      ::error ("%s: invalid format specified", who.c_str ());

    return do_printf (fmt_list, args, who);
  }

  int
  base_stream::puts (const std::string& s, const std::string& who)
  {
    int retval = -1;

    std::ostream *osp = preferred_output_stream ();

    if (! osp)
      invalid_operation (who, "writing");
    else
      {
        std::ostream& os = *osp;

        os << s;

        if (! os)
          error (who, "write error");
        else
          {
            // FIXME: why does this seem to be necessary?
            // Without it, output from a loop like
            //
            //   for i = 1:100, fputs (stdout, "foo\n"); endfor
            //
            // doesn't seem to go to the pager immediately.
            os.flush ();

            if (os)
              retval = 0;
            else
              error (who, "write error");
          }
      }

    return retval;
  }

  // Return current error message for this stream.

  std::string
  base_stream::error (bool clear_err, int& err_num)
  {
    err_num = (m_fail ? -1 : 0);

    std::string tmp = m_errmsg;

    if (clear_err)
      clear ();

    return tmp;
  }

  void
  base_stream::invalid_operation (const std::string& who, const char *rw)
  {
    // Note: This calls the member fcn error, not ::error from error.h.
    error (who, std::string ("stream not open for ") + rw);
  }

  int
  stream::flush (void)
  {
    int retval = -1;

    if (stream_ok ())
      retval = m_rep->flush ();

    return retval;
  }

  std::string
  stream::getl (octave_idx_type max_len, bool& err, const std::string& who)
  {
    std::string retval;

    if (stream_ok ())
      retval = m_rep->getl (max_len, err, who);

    return retval;
  }

  std::string
  stream::getl (const octave_value& tc_max_len, bool& err,
                const std::string& who)
  {
    err = false;

    int conv_err = 0;

    int max_len = -1;

    if (tc_max_len.is_defined ())
      {
        max_len = convert_to_valid_int (tc_max_len, conv_err);

        if (conv_err || max_len < 0)
          {
            err = true;
            ::error ("%s: invalid maximum length specified", who.c_str ());
          }
      }

    return getl (max_len, err, who);
  }

  std::string
  stream::gets (octave_idx_type max_len, bool& err, const std::string& who)
  {
    std::string retval;

    if (stream_ok ())
      retval = m_rep->gets (max_len, err, who);

    return retval;
  }

  std::string
  stream::gets (const octave_value& tc_max_len, bool& err,
                const std::string& who)
  {
    err = false;

    int conv_err = 0;

    int max_len = -1;

    if (tc_max_len.is_defined ())
      {
        max_len = convert_to_valid_int (tc_max_len, conv_err);

        if (conv_err || max_len < 0)
          {
            err = true;
            ::error ("%s: invalid maximum length specified", who.c_str ());
          }
      }

    return gets (max_len, err, who);
  }

  off_t
  stream::skipl (off_t count, bool& err, const std::string& who)
  {
    off_t retval = -1;

    if (stream_ok ())
      retval = m_rep->skipl (count, err, who);

    return retval;
  }

  off_t
  stream::skipl (const octave_value& tc_count, bool& err,
                 const std::string& who)
  {
    err = false;

    int conv_err = 0;

    int count = 1;

    if (tc_count.is_defined ())
      {
        if (tc_count.is_scalar_type ()
            && math::isinf (tc_count.scalar_value ()))
          count = -1;
        else
          {
            count = convert_to_valid_int (tc_count, conv_err);

            if (conv_err || count < 0)
              {
                err = true;
                ::error ("%s: invalid number of lines specified",
                         who.c_str ());
              }
          }
      }

    return skipl (count, err, who);
  }

  int
  stream::seek (off_t offset, int origin)
  {
    int status = -1;

    if (stream_ok ())
      {
        clearerr ();

        // Find current position so we can return to it if needed.
        off_t orig_pos = m_rep->tell ();

        // Move to end of file.  If successful, find the offset of the end.
        status = m_rep->seek (0, SEEK_END);

        if (status == 0)
          {
            off_t eof_pos = m_rep->tell ();

            if (origin == SEEK_CUR)
              {
                // Move back to original position, otherwise we will be seeking
                // from the end of file which is probably not the original
                // location.
                m_rep->seek (orig_pos, SEEK_SET);
              }

            // Attempt to move to desired position; may be outside bounds of
            // existing file.
            status = m_rep->seek (offset, origin);

            if (status == 0)
              {
                // Where are we after moving to desired position?
                off_t desired_pos = m_rep->tell ();

                // I don't think save_pos can be less than zero,
                // but we'll check anyway...
                if (desired_pos > eof_pos || desired_pos < 0)
                  {
                    // Seek outside bounds of file.
                    // Failure should leave position unchanged.
                    m_rep->seek (orig_pos, SEEK_SET);

                    status = -1;
                  }
              }
            else
              {
                // Seeking to the desired position failed.
                // Move back to original position and return failure status.
                m_rep->seek (orig_pos, SEEK_SET);

                status = -1;
              }
          }
      }

    return status;
  }

  int
  stream::seek (const octave_value& tc_offset,
                const octave_value& tc_origin)
  {
    int retval = -1;

    // FIXME: should we have octave_value methods that handle off_t explicitly?
    octave_int64 val = tc_offset.xint64_scalar_value ("fseek: invalid value for offset");
    off_t xoffset = val.value ();

    int conv_err = 0;

    int origin = SEEK_SET;

    if (tc_origin.is_string ())
      {
        std::string xorigin = tc_origin.xstring_value ("fseek: invalid value for origin");

        if (xorigin == "bof")
          origin = SEEK_SET;
        else if (xorigin == "cof")
          origin = SEEK_CUR;
        else if (xorigin == "eof")
          origin = SEEK_END;
        else
          conv_err = -1;
      }
    else
      {
        int xorigin = convert_to_valid_int (tc_origin, conv_err);

        if (! conv_err)
          {
            if (xorigin == -1)
              origin = SEEK_SET;
            else if (xorigin == 0)
              origin = SEEK_CUR;
            else if (xorigin == 1)
              origin = SEEK_END;
            else
              conv_err = -1;
          }
      }

    if (conv_err)
      ::error ("fseek: invalid value for origin");

    retval = seek (xoffset, origin);

    if (retval != 0)
      // Note: error is member fcn from stream, not ::error.
      error ("fseek: failed to seek to requested position");

    return retval;
  }

  off_t
  stream::tell (void)
  {
    off_t retval = -1;

    if (stream_ok ())
      retval = m_rep->tell ();

    return retval;
  }

  int
  stream::rewind (void)
  {
    return seek (0, SEEK_SET);
  }

  bool
  stream::is_open (void) const
  {
    bool retval = false;

    if (stream_ok ())
      retval = m_rep->is_open ();

    return retval;
  }

  void
  stream::close (void)
  {
    if (stream_ok ())
    {
      m_rep->flush ();
      m_rep->close ();
    }
  }

  template <typename SRC_T, typename DST_T>
  static octave_value
  convert_and_copy (std::list<void *>& input_buf_list,
                    octave_idx_type input_buf_elts,
                    octave_idx_type elts_read,
                    octave_idx_type nr, octave_idx_type nc, bool swap,
                    bool do_float_fmt_conv, bool do_NA_conv,
                    mach_info::float_format from_flt_fmt)
  {
    typedef typename DST_T::element_type dst_elt_type;

    DST_T conv (dim_vector (nr, nc));

    dst_elt_type *conv_data = conv.fortran_vec ();

    octave_idx_type j = 0;

    for (auto it = input_buf_list.cbegin (); it != input_buf_list.cend (); it++)
      {
        SRC_T *data = static_cast<SRC_T *> (*it);

        if (swap || do_float_fmt_conv)
          {
            if (do_NA_conv)
              {
                for (octave_idx_type i = 0; i < input_buf_elts && j < elts_read;
                     i++, j++)
                  {
                    if (swap)
                      swap_bytes<sizeof (SRC_T)> (&data[i]);
                    else if (do_float_fmt_conv)
                      do_float_format_conversion (&data[i], sizeof (SRC_T),
                                                  1, from_flt_fmt,
                                                  mach_info::native_float_format ());

                    // FIXME: Potentially add conversion code for MIPS NA here
                    //        Bug #59830.
                    // dst_elt_type tmp (data[i]);
                    // if (is_MIPS_NA (tmp))
                    //  tmp = replace_MIPS_NA (tmp);
                    // conv_data[j] = tmp;

                    conv_data[j] = data[i];
                  }
              }
            else
              {
                for (octave_idx_type i = 0; i < input_buf_elts && j < elts_read;
                     i++, j++)
                  {
                    if (swap)
                      swap_bytes<sizeof (SRC_T)> (&data[i]);
                    else if (do_float_fmt_conv)
                      do_float_format_conversion (&data[i], sizeof (SRC_T),
                                                  1, from_flt_fmt,
                                                  mach_info::native_float_format ());

                    conv_data[j] = data[i];
                  }
              }
          }
        else
          {
            if (do_NA_conv)
              {
                for (octave_idx_type i = 0; i < input_buf_elts && j < elts_read;
                     i++, j++)
                  {
                    // FIXME: Potentially add conversion code for MIPS NA here
                    conv_data[j] = data[i];
                  }
              }
            else
              {
                for (octave_idx_type i = 0; i < input_buf_elts && j < elts_read;
                     i++, j++)
                  conv_data[j] = data[i];
              }
          }

        delete [] data;
      }

    input_buf_list.clear ();

    for (octave_idx_type i = elts_read; i < nr * nc; i++)
      conv_data[i] = dst_elt_type (0);

    return conv;
  }

  typedef octave_value (*conv_fptr)
    (std::list<void *>& input_buf_list, octave_idx_type input_buf_elts,
     octave_idx_type elts_read, octave_idx_type nr, octave_idx_type nc,
     bool swap, bool do_float_fmt_conv, bool do_NA_conv,
     mach_info::float_format from_flt_fmt);

#define TABLE_ELT(T, U, V, W)                                           \
  conv_fptr_table[oct_data_conv::T][oct_data_conv::U] = convert_and_copy<V, W>

#define FILL_TABLE_ROW(T, V)                    \
  TABLE_ELT (T, dt_int8, V, int8NDArray);       \
  TABLE_ELT (T, dt_uint8, V, uint8NDArray);     \
  TABLE_ELT (T, dt_int16, V, int16NDArray);     \
  TABLE_ELT (T, dt_uint16, V, uint16NDArray);   \
  TABLE_ELT (T, dt_int32, V, int32NDArray);     \
  TABLE_ELT (T, dt_uint32, V, uint32NDArray);   \
  TABLE_ELT (T, dt_int64, V, int64NDArray);     \
  TABLE_ELT (T, dt_uint64, V, uint64NDArray);   \
  TABLE_ELT (T, dt_single, V, FloatNDArray);    \
  TABLE_ELT (T, dt_double, V, NDArray);         \
  TABLE_ELT (T, dt_char, V, charNDArray);       \
  TABLE_ELT (T, dt_schar, V, charNDArray);      \
  TABLE_ELT (T, dt_uchar, V, charNDArray);      \
  TABLE_ELT (T, dt_logical, V, boolNDArray);

  octave_value
  stream::finalize_read (std::list<void *>& input_buf_list,
                         octave_idx_type input_buf_elts,
                         octave_idx_type elts_read,
                         octave_idx_type nr, octave_idx_type nc,
                         oct_data_conv::data_type input_type,
                         oct_data_conv::data_type output_type,
                         mach_info::float_format ffmt)
  {
    octave_value retval;

    static bool initialized = false;

    // Table function pointers for return types x read types.

    static conv_fptr conv_fptr_table[oct_data_conv::dt_unknown][14];

    if (! initialized)
      {
        for (int i = 0; i < oct_data_conv::dt_unknown; i++)
          for (int j = 0; j < 14; j++)
            conv_fptr_table[i][j] = nullptr;

        FILL_TABLE_ROW (dt_int8, int8_t);
        FILL_TABLE_ROW (dt_uint8, uint8_t);
        FILL_TABLE_ROW (dt_int16, int16_t);
        FILL_TABLE_ROW (dt_uint16, uint16_t);
        FILL_TABLE_ROW (dt_int32, int32_t);
        FILL_TABLE_ROW (dt_uint32, uint32_t);
        FILL_TABLE_ROW (dt_int64, int64_t);
        FILL_TABLE_ROW (dt_uint64, uint64_t);
        FILL_TABLE_ROW (dt_single, float);
        FILL_TABLE_ROW (dt_double, double);
        FILL_TABLE_ROW (dt_char, char);
        FILL_TABLE_ROW (dt_schar, signed char);
        FILL_TABLE_ROW (dt_uchar, unsigned char);
        FILL_TABLE_ROW (dt_logical, bool);

        initialized = true;
      }

    bool swap = false;

    if (ffmt == mach_info::flt_fmt_unknown)
      ffmt = float_format ();

    if (mach_info::words_big_endian ())
      swap = (ffmt == mach_info::flt_fmt_ieee_little_endian);
    else
      swap = (ffmt == mach_info::flt_fmt_ieee_big_endian);

    bool do_float_fmt_conv = ((input_type == oct_data_conv::dt_double
                               || input_type == oct_data_conv::dt_single)
                              && ffmt != float_format ());

    bool do_NA_conv = (output_type == oct_data_conv::dt_double);

    switch (output_type)
      {
      case oct_data_conv::dt_int8:
      case oct_data_conv::dt_uint8:
      case oct_data_conv::dt_int16:
      case oct_data_conv::dt_uint16:
      case oct_data_conv::dt_int32:
      case oct_data_conv::dt_uint32:
      case oct_data_conv::dt_int64:
      case oct_data_conv::dt_uint64:
      case oct_data_conv::dt_single:
      case oct_data_conv::dt_double:
      case oct_data_conv::dt_char:
      case oct_data_conv::dt_schar:
      case oct_data_conv::dt_uchar:
      case oct_data_conv::dt_logical:
        {
          conv_fptr fptr = conv_fptr_table[input_type][output_type];

          retval = fptr (input_buf_list, input_buf_elts, elts_read,
                         nr, nc, swap, do_float_fmt_conv, do_NA_conv, ffmt);
        }
        break;

      default:
        ::error ("read: invalid type specification");
      }

    return retval;
  }

  octave_value
  stream::read (const Array<double>& size, octave_idx_type block_size,
                oct_data_conv::data_type input_type,
                oct_data_conv::data_type output_type,
                octave_idx_type skip, mach_info::float_format ffmt,
                octave_idx_type& count)
  {
    octave_value retval;

    if (! stream_ok ())
      return retval;

    octave_idx_type nr = -1;
    octave_idx_type nc = -1;

    bool one_elt_size_spec = false;

    // FIXME: We may eventually want to make this extensible.

    // FIXME: We need a better way to ensure that this numbering stays
    // consistent with the order of the elements in the data_type enum in the
    // oct_data_conv class.

    std::ptrdiff_t tmp_count = 0;

    try
      {
        get_size (size, nr, nc, one_elt_size_spec, "fread");
      }
    catch (const execution_exception&)
      {
        invalid_operation ("fread", "reading");

        return retval;
      }

    if (one_elt_size_spec)
      {
        // If NR == 0, Matlab returns [](0x0).

        // If NR > 0, the result will be a column vector with the given
        // number of rows.

        // If NR < 0, then we have Inf and the result will be a column
        // vector but we have to wait to see how big NR will be.

        if (nr == 0)
          nr = nc = 0;
        else
          nc = 1;
      }
    else
      {
        // Matlab returns [] even if there are two elements in the size
        // specification and one is nonzero.

        // If NC < 0 we have [NR, Inf] and we'll wait to decide how big NC
        // should be.

        if (nr == 0 || nc == 0)
          nr = nc = 0;
      }

    octave_idx_type elts_to_read = nr * nc;

    bool read_to_eof = elts_to_read < 0;

    octave_idx_type input_buf_elts = -1;

    if (skip == 0)
      {
        if (read_to_eof)
          input_buf_elts = 1024 * 1024;
        else
          input_buf_elts = elts_to_read;
      }
    else
      input_buf_elts = block_size;

    octave_idx_type input_elt_size
      = oct_data_conv::data_type_size (input_type);

    std::ptrdiff_t input_buf_size
      = static_cast<std::ptrdiff_t> (input_buf_elts) * input_elt_size;

    error_if (input_buf_size < 0);

    // Must also work and return correct type object for 0 elements to read.
    std::istream *isp = input_stream ();

    if (! isp)
      error ("fread: invalid input stream");
    else
      {
        std::istream& is = *isp;

        // Initialize eof_pos variable just once per function call
        off_t eof_pos = 0;
        off_t cur_pos = 0;
        if (skip != 0 && is && ! is.eof ())
          {
            cur_pos = is.tellg ();
            is.seekg (0, is.end);
            eof_pos = is.tellg ();
            is.seekg (cur_pos, is.beg);
          }

        std::list<void *> input_buf_list;

        while (is && ! is.eof ()
               && (read_to_eof || tmp_count < elts_to_read))
          {
            if (! read_to_eof)
              {
                octave_idx_type remaining_elts = elts_to_read - tmp_count;

                if (remaining_elts < input_buf_elts)
                  input_buf_size = remaining_elts * input_elt_size;
              }

            char *input_buf = new char [input_buf_size];

            is.read (input_buf, input_buf_size);

            std::size_t gcount = is.gcount ();

            cur_pos += gcount;

            octave_idx_type nel = gcount / input_elt_size;

            tmp_count += nel;

            input_buf_list.push_back (input_buf);

            if (skip != 0 && nel == block_size && is)
              {
                // Attempt to skip.
                // If skip would move past EOF, position at EOF.
                off_t remaining = eof_pos - cur_pos;

                if (remaining < skip)
                  {
                    is.seekg (0, is.end);
                    cur_pos = eof_pos;
                  }
                else
                  {
                    is.seekg (skip, is.cur);
                    cur_pos += skip;
                  }
              }
          }

        if (read_to_eof)
          {
            if (nc < 0)
              {
                nc = tmp_count / nr;

                if (tmp_count % nr != 0)
                  nc++;
              }
            else
              nr = tmp_count;
          }
        else if (tmp_count == 0)
          {
            nr = 0;
            nc = 0;
          }
        else if (tmp_count != nr * nc)
          {
            if (tmp_count % nr != 0)
              nc = tmp_count / nr + 1;
            else
              nc = tmp_count / nr;

            if (tmp_count < nr)
              nr = tmp_count;
          }

        if (tmp_count > std::numeric_limits<octave_idx_type>::max ())
          error ("fread: number of elements read exceeds max index size");
        else
          count = static_cast<octave_idx_type> (tmp_count);

        retval = finalize_read (input_buf_list, input_buf_elts, count,
                                nr, nc, input_type, output_type, ffmt);
      }

    return retval;
  }

  octave_idx_type
  stream::write (const octave_value& data, octave_idx_type block_size,
                 oct_data_conv::data_type output_type,
                 octave_idx_type skip, mach_info::float_format flt_fmt)
  {
    octave_idx_type retval = -1;

    if (! stream_ok ())
      invalid_operation ("fwrite", "writing");
    else
      {
        if (flt_fmt == mach_info::flt_fmt_unknown)
          flt_fmt = float_format ();

        octave_idx_type status = data.write (*this, block_size, output_type,
                                             skip, flt_fmt);

        if (status < 0)
          error ("fwrite: write error");
        else
          retval = status;
      }

    return retval;
  }

  template <typename T, typename V>
  static void
  convert_chars (const void *data, void *conv_data, octave_idx_type n_elts)
  {
    const T *tt_data = static_cast<const T *> (data);

    V *vt_data = static_cast<V *> (conv_data);

    for (octave_idx_type i = 0; i < n_elts; i++)
      vt_data[i] = tt_data[i];
  }

  template <typename T, typename V>
  static void
  convert_ints (const T *data, void *conv_data, octave_idx_type n_elts,
                bool swap)
  {
    typedef typename V::val_type val_type;

    val_type *vt_data = static_cast<val_type *> (conv_data);

    for (octave_idx_type i = 0; i < n_elts; i++)
      {
        // Yes, we want saturation semantics when converting to an integer type.
        V val (data[i]);

        vt_data[i] = val.value ();

        if (swap)
          swap_bytes<sizeof (val_type)> (&vt_data[i]);
      }
  }

  template <typename T>
  class ultimate_element_type
  {
  public:
    typedef T type;
  };

  template <typename T>
  class ultimate_element_type<octave_int<T>>
  {
  public:
    typedef T type;
  };

  template <typename T>
  static bool
  convert_data (const T *data, void *conv_data, octave_idx_type n_elts,
                oct_data_conv::data_type output_type,
                mach_info::float_format flt_fmt)
  {
    bool retval = true;

    bool swap = false;

    if (mach_info::words_big_endian ())
      swap = (flt_fmt == mach_info::flt_fmt_ieee_little_endian);
    else
      swap = (flt_fmt == mach_info::flt_fmt_ieee_big_endian);

    bool do_float_conversion = flt_fmt != mach_info::float_format ();

    typedef typename ultimate_element_type<T>::type ult_elt_type;

    switch (output_type)
      {
      case oct_data_conv::dt_char:
        convert_chars<ult_elt_type, char> (data, conv_data, n_elts);
        break;

      case oct_data_conv::dt_schar:
        convert_chars<ult_elt_type, signed char> (data, conv_data, n_elts);
        break;

      case oct_data_conv::dt_uchar:
        convert_chars<ult_elt_type, unsigned char> (data, conv_data, n_elts);
        break;

      case oct_data_conv::dt_int8:
        convert_ints<T, octave_int8> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_uint8:
        convert_ints<T, octave_uint8> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_int16:
        convert_ints<T, octave_int16> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_uint16:
        convert_ints<T, octave_uint16> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_int32:
        convert_ints<T, octave_int32> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_uint32:
        convert_ints<T, octave_uint32> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_int64:
        convert_ints<T, octave_int64> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_uint64:
        convert_ints<T, octave_uint64> (data, conv_data, n_elts, swap);
        break;

      case oct_data_conv::dt_single:
        {
          float *vt_data = static_cast<float *> (conv_data);

          for (octave_idx_type i = 0; i < n_elts; i++)
            {
              vt_data[i] = data[i];

              if (do_float_conversion)
                do_float_format_conversion (&vt_data[i], 1, flt_fmt);
            }
        }
        break;

      case oct_data_conv::dt_double:
        {
          double *vt_data = static_cast<double *> (conv_data);

          for (octave_idx_type i = 0; i < n_elts; i++)
            {
              vt_data[i] = data[i];

              if (do_float_conversion)
                do_double_format_conversion (&vt_data[i], 1, flt_fmt);
            }
        }
        break;

      default:
        ::error ("write: invalid type specification");
      }

    return retval;
  }

  bool
  stream::write_bytes (const void *data, std::size_t nbytes)
  {
    bool status = false;

    std::ostream *osp = output_stream ();

    if (osp)
      {
        std::ostream& os = *osp;

        if (os)
          {
            os.write (static_cast<const char *> (data), nbytes);

            if (os)
              status = true;
          }
      }

    return status;
  }

  bool
  stream::skip_bytes (std::size_t skip)
  {
    bool status = false;

    std::ostream *osp = output_stream ();

    if (! osp)
      return false;

    std::ostream& os = *osp;

    // Seek to skip when inside bounds of existing file.
    // Otherwise, write NUL to skip.
    off_t orig_pos = tell ();

    seek (0, SEEK_END);

    off_t eof_pos = tell ();

    // Is it possible for this to fail to return us to the original position?
    seek (orig_pos, SEEK_SET);

    std::size_t remaining = eof_pos - orig_pos;

    if (remaining < skip)
      {
        seek (0, SEEK_END);

        // FIXME: probably should try to write larger blocks...
        unsigned char zero = 0;
        for (std::size_t j = 0; j < skip - remaining; j++)
          os.write (reinterpret_cast<const char *> (&zero), 1);
      }
    else
      seek (skip, SEEK_CUR);

    if (os)
      status = true;

    return status;
  }

  template <typename T>
  octave_idx_type
  stream::write (const Array<T>& data, octave_idx_type block_size,
                 oct_data_conv::data_type output_type,
                 octave_idx_type skip,
                 mach_info::float_format flt_fmt)
  {
    bool swap = false;

    if (mach_info::words_big_endian ())
      swap = (flt_fmt == mach_info::flt_fmt_ieee_little_endian);
    else
      swap = (flt_fmt == mach_info::flt_fmt_ieee_big_endian);

    bool do_data_conversion = (swap || ! is_equivalent_type<T> (output_type)
                               || flt_fmt != mach_info::float_format ());

    octave_idx_type nel = data.numel ();

    octave_idx_type chunk_size;

    if (skip != 0)
      chunk_size = block_size;
    else if (do_data_conversion)
      chunk_size = 1024 * 1024;
    else
      chunk_size = nel;

    octave_idx_type i = 0;

    const T *pdata = data.data ();

    while (i < nel)
      {
        if (skip != 0)
          {
            if (! skip_bytes (skip))
              return -1;
          }

        octave_idx_type remaining_nel = nel - i;

        if (chunk_size > remaining_nel)
          chunk_size = remaining_nel;

        bool status = false;

        if (do_data_conversion)
          {
            std::size_t output_size
              = chunk_size * oct_data_conv::data_type_size (output_type);

            OCTAVE_LOCAL_BUFFER (unsigned char, conv_data, output_size);

            status = convert_data (&pdata[i], conv_data, chunk_size,
                                   output_type, flt_fmt);

            if (status)
              status = write_bytes (conv_data, output_size);
          }
        else
          status = write_bytes (pdata, sizeof (T) * chunk_size);

        if (! status)
          return -1;

        i += chunk_size;
      }

    return nel;
  }

#define INSTANTIATE_WRITE(T)                                            \
  template                                                              \
  OCTINTERP_API octave_idx_type                                         \
  stream::write (const Array<T>& data, octave_idx_type block_size,      \
                 oct_data_conv::data_type output_type,                  \
                 octave_idx_type skip,                                  \
                 mach_info::float_format flt_fmt)

  INSTANTIATE_WRITE (octave_int8);
  INSTANTIATE_WRITE (octave_uint8);
  INSTANTIATE_WRITE (octave_int16);
  INSTANTIATE_WRITE (octave_uint16);
  INSTANTIATE_WRITE (octave_int32);
  INSTANTIATE_WRITE (octave_uint32);
  INSTANTIATE_WRITE (octave_int64);
  INSTANTIATE_WRITE (octave_uint64);
  INSTANTIATE_WRITE (int8_t);
  INSTANTIATE_WRITE (uint8_t);
  INSTANTIATE_WRITE (int16_t);
  INSTANTIATE_WRITE (uint16_t);
  INSTANTIATE_WRITE (int32_t);
  INSTANTIATE_WRITE (uint32_t);
  INSTANTIATE_WRITE (int64_t);
  INSTANTIATE_WRITE (uint64_t);
  INSTANTIATE_WRITE (bool);
#if defined (OCTAVE_HAVE_OVERLOAD_CHAR_INT8_TYPES)
  INSTANTIATE_WRITE (char);
#endif
  INSTANTIATE_WRITE (float);
  INSTANTIATE_WRITE (double);

  octave_value
  stream::scanf (const std::string& fmt, const Array<double>& size,
                 octave_idx_type& count, const std::string& who)
  {
    octave_value retval;

    if (stream_ok ())
      retval = m_rep->scanf (fmt, size, count, who);

    return retval;
  }

  octave_value
  stream::scanf (const octave_value& fmt, const Array<double>& size,
                 octave_idx_type& count, const std::string& who)
  {
    octave_value retval = Matrix ();

    if (fmt.is_string ())
      {
        std::string sfmt = fmt.string_value ();

        if (fmt.is_sq_string ())
          sfmt = do_string_escapes (sfmt);

        retval = scanf (sfmt, size, count, who);
      }
    else
      {
        // Note: error is member fcn from stream, not ::error.
        error (who + ": format must be a string");
      }

    return retval;
  }

  octave_value_list
  stream::oscanf (const std::string& fmt, const std::string& who)
  {
    octave_value_list retval;

    if (stream_ok ())
      retval = m_rep->oscanf (fmt, who);

    return retval;
  }

  octave_value_list
  stream::oscanf (const octave_value& fmt, const std::string& who)
  {
    octave_value_list retval;

    if (fmt.is_string ())
      {
        std::string sfmt = fmt.string_value ();

        if (fmt.is_sq_string ())
          sfmt = do_string_escapes (sfmt);

        retval = oscanf (sfmt, who);
      }
    else
      {
        // Note: error is member fcn from stream, not ::error.
        error (who + ": format must be a string");
      }

    return retval;
  }

  octave_value
  stream::textscan (const std::string& fmt, octave_idx_type ntimes,
                    const octave_value_list& options,
                    const std::string& who, octave_idx_type& count)
  {
    return (stream_ok ()
            ? m_rep->do_textscan (fmt, ntimes, options, who, count)
            : octave_value ());
  }

  int
  stream::printf (const std::string& fmt, const octave_value_list& args,
                  const std::string& who)
  {
    int retval = -1;

    if (stream_ok ())
      retval = m_rep->printf (fmt, args, who);

    return retval;
  }

  int
  stream::printf (const octave_value& fmt, const octave_value_list& args,
                  const std::string& who)
  {
    int retval = 0;

    if (fmt.is_string ())
      {
        std::string sfmt = fmt.string_value ();

        if (fmt.is_sq_string ())
          sfmt = do_string_escapes (sfmt);

        retval = printf (sfmt, args, who);
      }
    else
      {
        // Note: error is member fcn from stream, not ::error.
        error (who + ": format must be a string");
      }

    return retval;
  }

  int
  stream::puts (const std::string& s, const std::string& who)
  {
    int retval = -1;

    if (stream_ok ())
      retval = m_rep->puts (s, who);

    return retval;
  }

  // FIXME: maybe this should work for string arrays too.

  int
  stream::puts (const octave_value& tc_s, const std::string& who)
  {
    int retval = -1;

    if (tc_s.is_string ())
      {
        std::string s = tc_s.string_value ();
        retval = puts (s, who);
      }
    else
      {
        // Note: error is member fcn from stream, not ::error.
        error (who + ": argument must be a string");
      }

    return retval;
  }

  bool
  stream::eof (void) const
  {
    int retval = -1;

    if (stream_ok ())
      retval = m_rep->eof ();

    return retval;
  }

  std::string
  stream::error (bool clear, int& err_num)
  {
    std::string retval = "invalid stream object";

    if (stream_ok (false))
      retval = m_rep->error (clear, err_num);

    return retval;
  }

  std::string
  stream::name (void) const
  {
    std::string retval;

    if (stream_ok ())
      retval = m_rep->name ();

    return retval;
  }

  int
  stream::mode (void) const
  {
    int retval = 0;

    if (stream_ok ())
      retval = m_rep->mode ();

    return retval;
  }

  mach_info::float_format
  stream::float_format (void) const
  {
    mach_info::float_format retval = mach_info::flt_fmt_unknown;

    if (stream_ok ())
      retval = m_rep->float_format ();

    return retval;
  }

  std::string
  stream::mode_as_string (int mode)
  {
    std::string retval = "???";
    std::ios::openmode in_mode = static_cast<std::ios::openmode> (mode);

    if (in_mode == std::ios::in)
      retval = "r";
    else if (in_mode == std::ios::out
             || in_mode == (std::ios::out | std::ios::trunc))
      retval = "w";
    else if (in_mode == (std::ios::out | std::ios::app))
      retval = "a";
    else if (in_mode == (std::ios::in | std::ios::out))
      retval = "r+";
    else if (in_mode == (std::ios::in | std::ios::out | std::ios::trunc))
      retval = "w+";
    else if (in_mode == (std::ios::in | std::ios::out | std::ios::ate))
      retval = "a+";
    else if (in_mode == (std::ios::in | std::ios::binary))
      retval = "rb";
    else if (in_mode == (std::ios::out | std::ios::binary)
             || in_mode == (std::ios::out | std::ios::trunc | std::ios::binary))
      retval = "wb";
    else if (in_mode == (std::ios::out | std::ios::app | std::ios::binary))
      retval = "ab";
    else if (in_mode == (std::ios::in | std::ios::out | std::ios::binary))
      retval = "r+b";
    else if (in_mode == (std::ios::in | std::ios::out | std::ios::trunc
                         | std::ios::binary))
      retval = "w+b";
    else if (in_mode == (std::ios::in | std::ios::out | std::ios::ate
                         | std::ios::binary))
      retval = "a+b";

    return retval;
  }

  stream_list::stream_list (interpreter& interp)
    : m_list (), m_lookup_cache (m_list.end ()), m_stdin_file (-1),
      m_stdout_file (-1), m_stderr_file (-1)
  {
    stream stdin_stream = istream::create (&std::cin, "stdin");

    // This uses octave_stdout (see pager.h), not std::cout so that
    // Octave's standard output stream will pass through the pager.

    // FIXME: we should be accessing octave_stdout from the interpreter.

    output_system& output_sys = interp.get_output_system ();

    stream stdout_stream
      = ostream::create (&(output_sys.__stdout__ ()), "stdout");

    stream stderr_stream = ostream::create (&std::cerr, "stderr");

    m_stdin_file = insert (stdin_stream);
    m_stdout_file = insert (stdout_stream);
    m_stderr_file = insert (stderr_stream);
  }

  stream_list::~stream_list (void)
  {
    clear ();
  }

  int stream_list::insert (stream& os)
  {
    // Insert item with key corresponding to file-descriptor.

    int stream_number = os.file_number ();

    if (stream_number == -1)
      return stream_number;

    // Should we test for
    //
    //  (m_list.find (stream_number) != m_list.end ()
    //   && m_list[stream_number].is_open ())
    //
    // and respond with "error ("internal error: ...")"?  It should not
    // happen except for some bug or if the user has opened a stream with
    // an interpreted command, but closed it directly with a system call
    // in an oct-file; then the kernel knows the fd is free, but Octave
    // does not know.  If it happens, it should not do harm here to simply
    // overwrite this entry, although the wrong entry might have done harm
    // before.

    if (m_list.size () >= m_list.max_size ())
      ::error ("could not create file id");

    m_list[stream_number] = os;

    return stream_number;
  }

  OCTAVE_NORETURN static
  void
  err_invalid_file_id (int fid, const std::string& who)
  {
    if (who.empty ())
      ::error ("invalid stream number = %d", fid);
    else
      ::error ("%s: invalid stream number = %d", who.c_str (), fid);
  }

  stream stream_list::lookup (int fid, const std::string& who) const
  {
    stream retval;

    if (fid < 0)
      err_invalid_file_id (fid, who);

    if (m_lookup_cache != m_list.end () && m_lookup_cache->first == fid)
      retval = m_lookup_cache->second;
    else
      {
        ostrl_map::const_iterator iter = m_list.find (fid);

        if (iter == m_list.end ())
          err_invalid_file_id (fid, who);

        retval = iter->second;
        m_lookup_cache = iter;
      }

    return retval;
  }

  stream stream_list::lookup (const octave_value& fid,
                              const std::string& who) const
  {
    int i = get_file_number (fid);

    return lookup (i, who);
  }

  int stream_list::remove (int fid, const std::string& who)
  {
    // Can't remove stdin (std::cin), stdout (std::cout), or stderr (std::cerr).
    if (fid < 3)
      err_invalid_file_id (fid, who);

    auto iter = m_list.find (fid);

    if (iter == m_list.end ())
      err_invalid_file_id (fid, who);

    stream os = iter->second;
    m_list.erase (iter);
    m_lookup_cache = m_list.end ();

    // FIXME: is this check redundant?
    if (! os.is_valid ())
      err_invalid_file_id (fid, who);

    os.close ();

    return 0;
  }

  int stream_list::remove (const octave_value& fid, const std::string& who)
  {
    int retval = -1;

    if (fid.is_string () && fid.string_value () == "all")
      {
        clear (false);

        retval = 0;
      }
    else
      {
        int i = get_file_number (fid);

        retval = remove (i, who);
      }

    return retval;
  }

  void stream_list::clear (bool flush)
  {
    if (flush)
      {
        // Flush stdout and stderr.
        m_list[1].flush ();
        m_list[2].flush ();
      }

    for (auto iter = m_list.begin (); iter != m_list.end (); )
      {
        int fid = iter->first;
        if (fid < 3)  // Don't delete stdin, stdout, stderr
          {
            iter++;
            continue;
          }

        stream os = iter->second;

        std::string name = os.name ();
        std::transform (name.begin (), name.end (), name.begin (), tolower);

        // FIXME: This test for gnuplot is hardly foolproof.
        if (name.find ("gnuplot") != std::string::npos)
          {
            // Don't close down pipes to gnuplot
            iter++;
            continue;
          }

        // Normal file handle.  Close and delete from m_list.
        if (os.is_valid ())
          os.close ();

        m_list.erase (iter++);
      }

    m_lookup_cache = m_list.end ();
  }

  string_vector stream_list::get_info (int fid) const
  {
    string_vector retval (4);

    if (fid < 0)
      return retval;

    stream os;
    if (m_lookup_cache != m_list.end () && m_lookup_cache->first == fid)
      os = m_lookup_cache->second;
    else
      {
        ostrl_map::const_iterator iter = m_list.find (fid);

        if (iter == m_list.end ())
          return retval;

        os = iter->second;
        m_lookup_cache = iter;
      }

    if (! os.is_valid ())
      return retval;

    retval(0) = os.name ();
    retval(1) = stream::mode_as_string (os.mode ());
    retval(2) = mach_info::float_format_as_string (os.float_format ());
    retval(3) = os.encoding ();

    return retval;
  }

  string_vector stream_list::get_info (const octave_value& fid) const
  {
    int conv_err = 0;

    if (fid.is_single_type ())
      ::error ("file id must be a file object or integer value");

    int int_fid = convert_to_valid_int (fid, conv_err);

    if (conv_err)
      ::error ("file id must be a file object or integer value");

    return get_info (int_fid);
  }

  std::string stream_list::list_open_files (void) const
  {
    std::ostringstream buf;

    buf << "\n"
        << "  number  mode  arch       name\n"
        << "  ------  ----  ----       ----\n";

    for (const auto& fid_strm : m_list)
      {
        stream os = fid_strm.second;

        buf << "  "
            << std::setiosflags (std::ios::right)
            << std::setw (4) << fid_strm.first << "     "
          // reset necessary in addition to setiosflags since this is one stmt.
            << std::resetiosflags (std::ios::adjustfield)
            << std::setiosflags (std::ios::left)
            << std::setw (3)
            << stream::mode_as_string (os.mode ())
            << "  "
            << std::setw (9)
            << mach_info::float_format_as_string (os.float_format ())
            << "  "
            << os.name () << "\n";
      }

    buf << "\n";

    return buf.str ();
  }

  octave_value stream_list::open_file_numbers (void) const
  {
    Matrix retval (1, m_list.size (), 0.0);

    int num_open = 0;

    for (const auto& fid_strm : m_list)
      {
        // Skip stdin, stdout, and stderr.
        if (fid_strm.first > 2 && fid_strm.second)
          retval(0, num_open++) = fid_strm.first;
      }

    retval.resize ((num_open > 0), num_open);

    return retval;
  }

  int stream_list::get_file_number (const octave_value& fid) const
  {
    int retval = -1;

    if (fid.is_string ())
      {
        std::string nm = fid.string_value ();

        for (const auto& fid_strm : m_list)
          {
            // stdin, stdout, and stderr are unnamed.
            if (fid_strm.first > 2)
              {
                stream os = fid_strm.second;

                if (os && os.name () == nm)
                  {
                    retval = fid_strm.first;
                    break;
                  }
              }
          }
      }
    else if (fid.is_single_type ())
      ::error ("file id must be a file object, std::string, or integer value");
    else
      {
        int conv_err = 0;

        int int_fid = convert_to_valid_int (fid, conv_err);

        if (conv_err)
          ::error ("file id must be a file object, std::string, or integer value");

        retval = int_fid;
      }

    return retval;
  }

  octave_value stream_list::stdin_file (void) const
  {
    return octave_value (m_stdin_file);
  }

  octave_value stream_list::stdout_file (void) const
  {
    return octave_value (m_stdout_file);
  }

  octave_value stream_list::stderr_file (void) const
  {
    return octave_value (m_stderr_file);
  }
}