fstream.tcc

Go to the documentation of this file.

// File based streams -*- C++ -*-

// Copyright (C) 1997-2025 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option)
// any later version.

// This library 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file bits/fstream.tcc
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{fstream}
 */

//
// ISO C++ 14882: 27.8  File-based streams
//

#ifndef _FSTREAM_TCC
#define _FSTREAM_TCC 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++11-extensions" // extern template

#include <bits/cxxabi_forced.h>
#include <bits/move.h>   // for swap
#include <cerrno>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  template<typename _CharT, typename _Traits>
    void
    basic_filebuf<_CharT, _Traits>::
    _M_allocate_internal_buffer()
    {
      // Allocate internal buffer only if one doesn't already exist
      // (either allocated or provided by the user via setbuf).
      if (!_M_buf_allocated && !_M_buf)
        {
          _M_buf = new char_type[_M_buf_size];
          _M_buf_allocated = true;
        }
    }

  template<typename _CharT, typename _Traits>
    void
    basic_filebuf<_CharT, _Traits>::
    _M_destroy_internal_buffer() throw()
    {
      if (_M_buf_allocated)
        {
          delete [] _M_buf;
          _M_buf = 0;
          _M_buf_allocated = false;
        }
      delete [] _M_ext_buf;
      _M_ext_buf = 0;
      _M_ext_buf_size = 0;
      _M_ext_next = 0;
      _M_ext_end = 0;
    }

  template<typename _CharT, typename _Traits>
    basic_filebuf<_CharT, _Traits>::
    basic_filebuf() : __streambuf_type(), _M_lock(), _M_file(&_M_lock),
    _M_mode(ios_base::openmode(0)), _M_state_beg(), _M_state_cur(),
    _M_state_last(), _M_buf(0), _M_buf_size(_GLIBCXX_BUFSIZ),
    _M_buf_allocated(false), _M_reading(false), _M_writing(false), _M_pback(), 
    _M_pback_cur_save(0), _M_pback_end_save(0), _M_pback_init(false),
    _M_codecvt(0), _M_ext_buf(0), _M_ext_buf_size(0), _M_ext_next(0),
    _M_ext_end(0)
    {
      _M_codecvt = std::__try_use_facet<__codecvt_type>(this->_M_buf_locale);
    }

#if __cplusplus >= 201103L
  template<typename _CharT, typename _Traits>
    basic_filebuf<_CharT, _Traits>::
    basic_filebuf(basic_filebuf&& __rhs)
    : __streambuf_type(__rhs),
    _M_lock(), _M_file(std::move(__rhs._M_file), &_M_lock),
    _M_mode(std::__exchange(__rhs._M_mode, ios_base::openmode(0))),
    _M_state_beg(std::move(__rhs._M_state_beg)),
    _M_state_cur(std::move(__rhs._M_state_cur)),
    _M_state_last(std::move(__rhs._M_state_last)),
    _M_buf(std::__exchange(__rhs._M_buf, nullptr)),
    _M_buf_size(std::__exchange(__rhs._M_buf_size, 1)),
    _M_buf_allocated(std::__exchange(__rhs._M_buf_allocated, false)),
    _M_reading(std::__exchange(__rhs._M_reading, false)),
    _M_writing(std::__exchange(__rhs._M_writing, false)),
    _M_pback(__rhs._M_pback),
    _M_pback_cur_save(std::__exchange(__rhs._M_pback_cur_save, nullptr)),
    _M_pback_end_save(std::__exchange(__rhs._M_pback_end_save, nullptr)),
    _M_pback_init(std::__exchange(__rhs._M_pback_init, false)),
    _M_codecvt(__rhs._M_codecvt),
    _M_ext_buf(std::__exchange(__rhs._M_ext_buf, nullptr)),
    _M_ext_buf_size(std::__exchange(__rhs._M_ext_buf_size, 0)),
    _M_ext_next(std::__exchange(__rhs._M_ext_next, nullptr)),
    _M_ext_end(std::__exchange(__rhs._M_ext_end, nullptr))
    {
      __rhs._M_set_buffer(-1);
      __rhs._M_state_last = __rhs._M_state_cur = __rhs._M_state_beg;
    }

  template<typename _CharT, typename _Traits>
    basic_filebuf<_CharT, _Traits>&
    basic_filebuf<_CharT, _Traits>::
    operator=(basic_filebuf&& __rhs)
    {
      this->close();
      __streambuf_type::operator=(__rhs);
      _M_file.swap(__rhs._M_file);
      _M_mode = std::__exchange(__rhs._M_mode, ios_base::openmode(0));
      _M_state_beg = std::move(__rhs._M_state_beg);
      _M_state_cur = std::move(__rhs._M_state_cur);
      _M_state_last = std::move(__rhs._M_state_last);
      _M_buf = std::__exchange(__rhs._M_buf, nullptr);
      _M_buf_size = std::__exchange(__rhs._M_buf_size, 1);
      _M_buf_allocated = std::__exchange(__rhs._M_buf_allocated, false);
      _M_ext_buf = std::__exchange(__rhs._M_ext_buf, nullptr);
      _M_ext_buf_size = std::__exchange(__rhs._M_ext_buf_size, 0);
      _M_ext_next = std::__exchange(__rhs._M_ext_next, nullptr);
      _M_ext_end = std::__exchange(__rhs._M_ext_end, nullptr);
      _M_reading = std::__exchange(__rhs._M_reading, false);
      _M_writing = std::__exchange(__rhs._M_writing, false);
      _M_pback_cur_save = std::__exchange(__rhs._M_pback_cur_save, nullptr);
      _M_pback_end_save = std::__exchange(__rhs._M_pback_end_save, nullptr);
      _M_pback_init = std::__exchange(__rhs._M_pback_init, false);
      __rhs._M_set_buffer(-1);
      __rhs._M_state_last = __rhs._M_state_cur = __rhs._M_state_beg;
      return *this;
    }

  template<typename _CharT, typename _Traits>
    void
    basic_filebuf<_CharT, _Traits>::
    swap(basic_filebuf& __rhs)
    {
      __streambuf_type::swap(__rhs);
      _M_file.swap(__rhs._M_file);
      std::swap(_M_mode, __rhs._M_mode);
      std::swap(_M_state_beg, __rhs._M_state_beg);
      std::swap(_M_state_cur, __rhs._M_state_cur);
      std::swap(_M_state_last, __rhs._M_state_last);
      std::swap(_M_buf, __rhs._M_buf);
      std::swap(_M_buf_size, __rhs._M_buf_size);
      std::swap(_M_buf_allocated, __rhs._M_buf_allocated);
      std::swap(_M_ext_buf, __rhs._M_ext_buf);
      std::swap(_M_ext_buf_size, __rhs._M_ext_buf_size);
      std::swap(_M_ext_next, __rhs._M_ext_next);
      std::swap(_M_ext_end, __rhs._M_ext_end);
      std::swap(_M_reading, __rhs._M_reading);
      std::swap(_M_writing, __rhs._M_writing);
      std::swap(_M_pback_cur_save, __rhs._M_pback_cur_save);
      std::swap(_M_pback_end_save, __rhs._M_pback_end_save);
      std::swap(_M_pback_init, __rhs._M_pback_init);
    }
#endif

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::__filebuf_type*
    basic_filebuf<_CharT, _Traits>::
    open(const char* __s, ios_base::openmode __mode)
    {
      __filebuf_type *__ret = 0;
      if (!this->is_open())
        {
          _M_file.open(__s, __mode);
          if (this->is_open())
            {
              _M_allocate_internal_buffer();
              _M_mode = __mode;

              // Setup initial buffer to 'uncommitted' mode.
              _M_reading = false;
              _M_writing = false;
              _M_set_buffer(-1);

              // Reset to initial state.
              _M_state_last = _M_state_cur = _M_state_beg;

              // 27.8.1.3,4
              if ((__mode & ios_base::ate)
                  && this->seekoff(0, ios_base::end, __mode)
                  == pos_type(off_type(-1)))
                this->close();
              else
                __ret = this;
            }
        }
      return __ret;
    }

#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
  template<typename _CharT, typename _Traits>
    basic_filebuf<_CharT, _Traits>*
    basic_filebuf<_CharT, _Traits>::
    open(const wchar_t* __s, ios_base::openmode __mode)
    {
      __filebuf_type *__ret = 0;
      if (!this->is_open())
        {
          _M_file.open(__s, __mode);
          if (this->is_open())
            {
              _M_allocate_internal_buffer();
              _M_mode = __mode;

              // Setup initial buffer to 'uncommitted' mode.
              _M_reading = false;
              _M_writing = false;
              _M_set_buffer(-1);

              // Reset to initial state.
              _M_state_last = _M_state_cur = _M_state_beg;

              // 27.8.1.3,4
              if ((__mode & ios_base::ate)
                  && this->seekoff(0, ios_base::end, __mode)
                  == pos_type(off_type(-1)))
                this->close();
              else
                __ret = this;
            }
        }
      return __ret;
    }
#endif // HAVE__WFOPEN && USE_WCHAR_T

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::__filebuf_type*
    basic_filebuf<_CharT, _Traits>::
    close()
    {
      if (!this->is_open())
        return 0;

      bool __testfail = false;
      {
        // NB: Do this here so that re-opened filebufs will be cool...
        struct __close_sentry
        {
          basic_filebuf *__fb;
          __close_sentry (basic_filebuf *__fbi): __fb(__fbi) { }
          ~__close_sentry ()
          {
            __fb->_M_mode = ios_base::openmode(0);
            __fb->_M_pback_init = false;
            __fb->_M_destroy_internal_buffer();
            __fb->_M_reading = false;
            __fb->_M_writing = false;
            __fb->_M_set_buffer(-1);
            __fb->_M_state_last = __fb->_M_state_cur = __fb->_M_state_beg;
          }
        } __cs (this);

        __try
          {
            if (!_M_terminate_output())
              __testfail = true;
          }
        __catch(...)
          {
            _M_file.close();
            __throw_exception_again;
          }
      }

      if (!_M_file.close())
        __testfail = true;

      if (__testfail)
        return 0;
      else
        return this;
    }

  template<typename _CharT, typename _Traits>
    streamsize
    basic_filebuf<_CharT, _Traits>::
    showmanyc()
    {
      streamsize __ret = -1;
      const bool __testin = _M_mode & ios_base::in;
      if (__testin && this->is_open())
        {
          // For a stateful encoding (-1) the pending sequence might be just
          // shift and unshift prefixes with no actual character.
          __ret = this->egptr() - this->gptr();

#if _GLIBCXX_HAVE_DOS_BASED_FILESYSTEM
          // About this workaround, see libstdc++/20806.
          const bool __testbinary = _M_mode & ios_base::binary;
          if (__check_facet(_M_codecvt).encoding() >= 0
              && __testbinary)
#else
          if (__check_facet(_M_codecvt).encoding() >= 0)
#endif
            __ret += _M_file.showmanyc() / _M_codecvt->max_length();
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::int_type
    basic_filebuf<_CharT, _Traits>::
    underflow()
    {
      int_type __ret = traits_type::eof();
      const bool __testin = _M_mode & ios_base::in;
      if (__testin)
        {
          if (_M_writing)
            {
              if (overflow() == traits_type::eof())
                return __ret;
              _M_set_buffer(-1);
              _M_writing = false;
            }
          // Check for pback madness, and if so switch back to the
          // normal buffers and jet outta here before expensive
          // fileops happen...
          _M_destroy_pback();

          if (this->gptr() < this->egptr())
            return traits_type::to_int_type(*this->gptr());

          // Get and convert input sequence.
          const size_t __buflen = _M_buf_size > 1 ? _M_buf_size - 1 : 1;

          // Will be set to true if ::read() returns 0 indicating EOF.
          bool __got_eof = false;
          // Number of internal characters produced.
          streamsize __ilen = 0;
          codecvt_base::result __r = codecvt_base::ok;
          if (__check_facet(_M_codecvt).always_noconv())
            {
              __ilen = _M_file.xsgetn(reinterpret_cast<char*>(this->eback()),
                                      __buflen);
              if (__ilen == 0)
                __got_eof = true;
            }
          else
            {
              // Worst-case number of external bytes.
              // XXX Not done encoding() == -1.
              const int __enc = _M_codecvt->encoding();
              streamsize __blen; // Minimum buffer size.
              streamsize __rlen; // Number of chars to read.
              if (__enc > 0)
                __blen = __rlen = __buflen * __enc;
              else
                {
                  __blen = __buflen + _M_codecvt->max_length() - 1;
                  __rlen = __buflen;
                }
              const streamsize __remainder = _M_ext_end - _M_ext_next;
              __rlen = __rlen > __remainder ? __rlen - __remainder : 0;

              // An imbue in 'read' mode implies first converting the external
              // chars already present.
              if (_M_reading && this->egptr() == this->eback() && __remainder)
                __rlen = 0;

              // Allocate buffer if necessary and move unconverted
              // bytes to front.
              if (_M_ext_buf_size < __blen)
                {
                  char* __buf = new char[__blen];
                  if (__remainder)
                    __builtin_memcpy(__buf, _M_ext_next, __remainder);

                  delete [] _M_ext_buf;
                  _M_ext_buf = __buf;
                  _M_ext_buf_size = __blen;
                }
              else if (__remainder)
                __builtin_memmove(_M_ext_buf, _M_ext_next, __remainder);

              _M_ext_next = _M_ext_buf;
              _M_ext_end = _M_ext_buf + __remainder;
              _M_state_last = _M_state_cur;

              do
                {
                  if (__rlen > 0)
                    {
                      // Sanity check!
                      // This may fail if the return value of
                      // codecvt::max_length() is bogus.
                      if (_M_ext_end - _M_ext_buf + __rlen > _M_ext_buf_size)
                        {
                          __throw_ios_failure(__N("basic_filebuf::underflow "
                                              "codecvt::max_length() "
                                              "is not valid"));
                        }
                      streamsize __elen = _M_file.xsgetn(_M_ext_end, __rlen);
                      if (__elen == 0)
                        __got_eof = true;
                      else if (__elen == -1)
                        break;
                      _M_ext_end += __elen;
                    }

                  char_type* __iend = this->eback();
                  if (_M_ext_next < _M_ext_end)
                    __r = _M_codecvt->in(_M_state_cur, _M_ext_next,
                                         _M_ext_end, _M_ext_next,
                                         this->eback(),
                                         this->eback() + __buflen, __iend);
                  if (__r == codecvt_base::noconv)
                    {
                      size_t __avail = _M_ext_end - _M_ext_buf;
                      __ilen = std::min(__avail, __buflen);
                      traits_type::copy(this->eback(),
                                        reinterpret_cast<char_type*>
                                        (_M_ext_buf), __ilen);
                      _M_ext_next = _M_ext_buf + __ilen;
                    }
                  else
                    __ilen = __iend - this->eback();

                  // _M_codecvt->in may return error while __ilen > 0: this is
                  // ok, and actually occurs in case of mixed encodings (e.g.,
                  // XML files).
                  if (__r == codecvt_base::error)
                    break;

                  __rlen = 1;
                }
              while (__ilen == 0 && !__got_eof);
            }

          if (__ilen > 0)
            {
              _M_set_buffer(__ilen);
              _M_reading = true;
              __ret = traits_type::to_int_type(*this->gptr());
            }
          else if (__got_eof)
            {
              // If the actual end of file is reached, set 'uncommitted'
              // mode, thus allowing an immediate write without an
              // intervening seek.
              _M_set_buffer(-1);
              _M_reading = false;
              // However, reaching it while looping on partial means that
              // the file has got an incomplete character.
              if (__r == codecvt_base::partial)
                __throw_ios_failure(__N("basic_filebuf::underflow "
                                    "incomplete character in file"));
            }
          else if (__r == codecvt_base::error)
            __throw_ios_failure(__N("basic_filebuf::underflow "
                                "invalid byte sequence in file"));
          else
            __throw_ios_failure(__N("basic_filebuf::underflow "
                                "error reading the file"), errno);
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::int_type
    basic_filebuf<_CharT, _Traits>::
    pbackfail(int_type __i)
    {
      int_type __ret = traits_type::eof();
      const bool __testin = _M_mode & ios_base::in;
      if (__testin)
        {
          if (_M_writing)
            {
              if (overflow() == traits_type::eof())
                return __ret;
              _M_set_buffer(-1);
              _M_writing = false;
            }
          // Remember whether the pback buffer is active, otherwise below
          // we may try to store in it a second char (libstdc++/9761).
          const bool __testpb = _M_pback_init;
          const bool __testeof = traits_type::eq_int_type(__i, __ret);
          int_type __tmp;
          if (this->eback() < this->gptr())
            {
              this->gbump(-1);
              __tmp = traits_type::to_int_type(*this->gptr());
            }
          else if (this->seekoff(-1, ios_base::cur) != pos_type(off_type(-1)))
            {
              __tmp = this->underflow();
              if (traits_type::eq_int_type(__tmp, __ret))
                return __ret;
            }
          else
            {
              // At the beginning of the buffer, need to make a
              // putback position available.  But the seek may fail
              // (f.i., at the beginning of a file, see
              // libstdc++/9439) and in that case we return
              // traits_type::eof().
              return __ret;
            }

          // Try to put back __i into input sequence in one of three ways.
          // Order these tests done in is unspecified by the standard.
          if (!__testeof && traits_type::eq_int_type(__i, __tmp))
            __ret = __i;
          else if (__testeof)
            __ret = traits_type::not_eof(__i);
          else if (!__testpb)
            {
              _M_create_pback();
              _M_reading = true;
              *this->gptr() = traits_type::to_char_type(__i);
              __ret = __i;
            }
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::int_type
    basic_filebuf<_CharT, _Traits>::
    overflow(int_type __c)
    {
      int_type __ret = traits_type::eof();
      const bool __testeof = traits_type::eq_int_type(__c, __ret);
      const bool __testout = (_M_mode & ios_base::out
                              || _M_mode & ios_base::app);
      if (__testout)
        {
          if (_M_reading)
            {
              _M_destroy_pback();
              const int __gptr_off = _M_get_ext_pos(_M_state_last);
              if (_M_seek(__gptr_off, ios_base::cur, _M_state_last)
                  == pos_type(off_type(-1)))
                return __ret;
            }
          if (this->pbase() < this->pptr())
            {
              // If appropriate, append the overflow char.
              if (!__testeof)
                {
                  *this->pptr() = traits_type::to_char_type(__c);
                  this->pbump(1);
                }

              // Convert pending sequence to external representation,
              // and output.
              if (_M_convert_to_external(this->pbase(),
                                         this->pptr() - this->pbase()))
                {
                  _M_set_buffer(0);
                  __ret = traits_type::not_eof(__c);
                }
            }
          else if (_M_buf_size > 1)
            {
              // Overflow in 'uncommitted' mode: set _M_writing, set
              // the buffer to the initial 'write' mode, and put __c
              // into the buffer.
              _M_set_buffer(0);
              _M_writing = true;
              if (!__testeof)
                {
                  *this->pptr() = traits_type::to_char_type(__c);
                  this->pbump(1);
                }
              __ret = traits_type::not_eof(__c);
            }
          else
            {
              // Unbuffered.
              char_type __conv = traits_type::to_char_type(__c);
              if (__testeof || _M_convert_to_external(&__conv, 1))
                {
                  _M_writing = true;
                  __ret = traits_type::not_eof(__c);
                }
            }
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    bool
    basic_filebuf<_CharT, _Traits>::
    _M_convert_to_external(_CharT* __ibuf, streamsize __ilen)
    {
      // Sizes of external and pending output.
      streamsize __elen;
      streamsize __plen;
      if (__check_facet(_M_codecvt).always_noconv())
        {
          __elen = _M_file.xsputn(reinterpret_cast<char*>(__ibuf), __ilen);
          __plen = __ilen;
        }
      else
        {
          // Worst-case number of external bytes needed.
          // XXX Not done encoding() == -1.
          streamsize __blen = __ilen * _M_codecvt->max_length();
          char* __buf = static_cast<char*>(__builtin_alloca(__blen));

          char* __bend;
          const char_type* __iend;
          codecvt_base::result __r;
          __r = _M_codecvt->out(_M_state_cur, __ibuf, __ibuf + __ilen,
                                __iend, __buf, __buf + __blen, __bend);

          if (__r == codecvt_base::ok || __r == codecvt_base::partial)
            __blen = __bend - __buf;
          else if (__r == codecvt_base::noconv)
            {
              // Same as the always_noconv case above.
              __buf = reinterpret_cast<char*>(__ibuf);
              __blen = __ilen;
            }
          else
            __throw_ios_failure(__N("basic_filebuf::_M_convert_to_external "
                                    "conversion error"));
  
          __elen = _M_file.xsputn(__buf, __blen);
          __plen = __blen;

          // Try once more for partial conversions.
          if (__r == codecvt_base::partial && __elen == __plen)
            {
              const char_type* __iresume = __iend;
              streamsize __rlen = this->pptr() - __iend;
              __r = _M_codecvt->out(_M_state_cur, __iresume,
                                    __iresume + __rlen, __iend, __buf,
                                    __buf + __blen, __bend);
              if (__r != codecvt_base::error)
                {
                  __rlen = __bend - __buf;
                  __elen = _M_file.xsputn(__buf, __rlen);
                  __plen = __rlen;
                }
              else
                __throw_ios_failure(__N("basic_filebuf::_M_convert_to_external "
                                        "conversion error"));
            }
        }
      return __elen == __plen;
    }

  template<typename _CharT, typename _Traits>
    streamsize
    basic_filebuf<_CharT, _Traits>::
    xsgetn(_CharT* __s, streamsize __n)
    {
      // Clear out pback buffer before going on to the real deal...
      streamsize __ret = 0;
      if (_M_pback_init)
        {
          if (__n > 0 && this->gptr() == this->eback())
            {
              *__s++ = *this->gptr(); // emulate non-underflowing sbumpc
              this->gbump(1);
              __ret = 1;
              --__n;
            }
          _M_destroy_pback();
        }
      else if (_M_writing)
        {
          if (overflow() == traits_type::eof())
            return __ret;
          _M_set_buffer(-1);
          _M_writing = false;
        }
 
      // Optimization in the always_noconv() case, to be generalized in the
      // future: when __n > __buflen we read directly instead of using the
      // buffer repeatedly.
      const bool __testin = _M_mode & ios_base::in;
      const streamsize __buflen = _M_buf_size > 1 ? _M_buf_size - 1 : 1;
 
      if (__n > __buflen && __check_facet(_M_codecvt).always_noconv()
          && __testin)
        {
          // First, copy the chars already present in the buffer.
          const streamsize __avail = this->egptr() - this->gptr();
          if (__avail != 0)
            {
              traits_type::copy(__s, this->gptr(), __avail);
              __s += __avail;
              this->setg(this->eback(), this->gptr() + __avail, this->egptr());
              __ret += __avail;
              __n -= __avail;
            }
 
          // Need to loop in case of short reads (relatively common
          // with pipes).
          streamsize __len;
          for (;;)
            {
              __len = _M_file.xsgetn(reinterpret_cast<char*>(__s), __n);
              if (__len == -1)
                __throw_ios_failure(__N("basic_filebuf::xsgetn "
                                        "error reading the file"), errno);
              if (__len == 0)
                break;
 
              __n -= __len;
              __ret += __len;
              if (__n == 0)
                break;

              __s += __len;
            }

          if (__n == 0)
            {
              // Set _M_reading. Buffer is already in initial 'read' mode.
              _M_reading = true;
            }
          else if (__len == 0)
            {
              // If end of file is reached, set 'uncommitted'
              // mode, thus allowing an immediate write without
              // an intervening seek.
              _M_set_buffer(-1);
              _M_reading = false;
            }
        }
      else
        __ret += __streambuf_type::xsgetn(__s, __n);
 
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    streamsize
    basic_filebuf<_CharT, _Traits>::
    xsputn(const _CharT* __s, streamsize __n)
    {
      streamsize __ret = 0;
      // Optimization in the always_noconv() case, to be generalized in the
      // future: when __n is larger than the available capacity we write
      // directly instead of using the buffer.
      const bool __testout = (_M_mode & ios_base::out
                              || _M_mode & ios_base::app);
      if (__check_facet(_M_codecvt).always_noconv()
          && __testout && !_M_reading)
        {
          streamsize __bufavail = this->epptr() - this->pptr();

          // Don't mistake 'uncommitted' mode buffered with unbuffered.
          if (!_M_writing && _M_buf_size > 1)
            __bufavail = _M_buf_size - 1;

          if (__n >= __bufavail)
            {
              const streamsize __buffill = this->pptr() - this->pbase();
              const char* __buf = reinterpret_cast<const char*>(this->pbase());
              __ret = _M_file.xsputn_2(__buf, __buffill,
                                       reinterpret_cast<const char*>(__s),
                                       __n);
              if (__ret == __buffill + __n)
                {
                  _M_set_buffer(0);
                  _M_writing = true;
                }
              if (__ret > __buffill)
                __ret -= __buffill;
              else
                __ret = 0;
            }
          else
            __ret = __streambuf_type::xsputn(__s, __n);
        }
       else
         __ret = __streambuf_type::xsputn(__s, __n);
       return __ret;
    }

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::__streambuf_type*
    basic_filebuf<_CharT, _Traits>::
    setbuf(char_type* __s, streamsize __n)
    {
      if (!this->is_open())
        {
          if (__s == 0 && __n == 0)
            _M_buf_size = 1;
          else if (__s && __n > 0)
            {
              // This is implementation-defined behavior, and assumes that
              // an external char_type array of length __n exists and has
              // been pre-allocated. If this is not the case, things will
              // quickly blow up. When __n > 1, __n - 1 positions will be
              // used for the get area, __n - 1 for the put area and 1
              // position to host the overflow char of a full put area.
              // When __n == 1, 1 position will be used for the get area
              // and 0 for the put area, as in the unbuffered case above.
              _M_buf = __s;
              _M_buf_size = __n;
            }
        }
      return this;
    }


  // According to 27.8.1.4 p11 - 13, seekoff should ignore the last
  // argument (of type openmode).
  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::pos_type
    basic_filebuf<_CharT, _Traits>::
    seekoff(off_type __off, ios_base::seekdir __way, ios_base::openmode)
    {
      int __width = 0;
      if (_M_codecvt)
        __width = _M_codecvt->encoding();
      if (__width < 0)
        __width = 0;

      pos_type __ret = pos_type(off_type(-1));
      const bool __testfail = __off != 0 && __width <= 0;
      if (this->is_open() && !__testfail)
        {
          // tellg and tellp queries do not affect any state, unless
          // ! always_noconv and the put sequence is not empty.
          // In that case, determining the position requires converting the
          // put sequence. That doesn't use ext_buf, so requires a flush.
          bool __no_movement = __way == ios_base::cur && __off == 0
            && (!_M_writing || _M_codecvt->always_noconv());

          // Ditch any pback buffers to avoid confusion.
          if (!__no_movement)
            _M_destroy_pback();

          // Correct state at destination. Note that this is the correct
          // state for the current position during output, because
          // codecvt::unshift() returns the state to the initial state.
          // This is also the correct state at the end of the file because
          // an unshift sequence should have been written at the end.
          __state_type __state = _M_state_beg;
          off_type __computed_off = __off * __width;
          if (_M_reading && __way == ios_base::cur)
            {
              __state = _M_state_last;
              __computed_off += _M_get_ext_pos(__state);
            }
          if (!__no_movement)
            __ret = _M_seek(__computed_off, __way, __state);
          else
            {
              if (_M_writing)
                __computed_off = this->pptr() - this->pbase();
              
              off_type __file_off = _M_file.seekoff(0, ios_base::cur);
              if (__file_off != off_type(-1))
                {
                  __ret = __file_off + __computed_off;
                  __ret.state(__state);
                }
            }
        }
      return __ret;
    }

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 171. Strange seekpos() semantics due to joint position
  // According to the resolution of DR 171, seekpos should ignore the last
  // argument (of type openmode).
  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::pos_type
    basic_filebuf<_CharT, _Traits>::
    seekpos(pos_type __pos, ios_base::openmode)
    {
      pos_type __ret =  pos_type(off_type(-1));
      if (this->is_open())
        {
          // Ditch any pback buffers to avoid confusion.
          _M_destroy_pback();
          __ret = _M_seek(off_type(__pos), ios_base::beg, __pos.state());
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    typename basic_filebuf<_CharT, _Traits>::pos_type
    basic_filebuf<_CharT, _Traits>::
    _M_seek(off_type __off, ios_base::seekdir __way, __state_type __state)
    {
      pos_type __ret = pos_type(off_type(-1));
      if (_M_terminate_output())
        {
          off_type __file_off = _M_file.seekoff(__off, __way);
          if (__file_off != off_type(-1))
            {
              _M_reading = false;
              _M_writing = false;
              _M_ext_next = _M_ext_end = _M_ext_buf;
              _M_set_buffer(-1);
              _M_state_cur = __state;
              __ret = __file_off;
              __ret.state(_M_state_cur);
            }
        }
      return __ret;
    }

  // Returns the distance from the end of the ext buffer to the point
  // corresponding to gptr(). This is a negative value. Updates __state
  // from eback() correspondence to gptr().
  template<typename _CharT, typename _Traits>
    int basic_filebuf<_CharT, _Traits>::
    _M_get_ext_pos(__state_type& __state)
    {
      if (_M_codecvt->always_noconv())
        return this->gptr() - this->egptr();
      else
        {
          // Calculate offset from _M_ext_buf that corresponds to
          // gptr(). Precondition: __state == _M_state_last, which
          // corresponds to eback().
          const int __gptr_off =
            _M_codecvt->length(__state, _M_ext_buf, _M_ext_next,
                               this->gptr() - this->eback());
          return _M_ext_buf + __gptr_off - _M_ext_end;
        }
    }
    
  template<typename _CharT, typename _Traits>
    bool
    basic_filebuf<_CharT, _Traits>::
    _M_terminate_output()
    {
      // Part one: update the output sequence.
      bool __testvalid = true;
      if (this->pbase() < this->pptr())
        {
          const int_type __tmp = this->overflow();
          if (traits_type::eq_int_type(__tmp, traits_type::eof()))
            __testvalid = false;
        }

      // Part two: output unshift sequence.
      if (_M_writing && !__check_facet(_M_codecvt).always_noconv()
          && __testvalid)
        {
          // Note: this value is arbitrary, since there is no way to
          // get the length of the unshift sequence from codecvt,
          // without calling unshift.
          const size_t __blen = 128;
          char __buf[__blen];
          codecvt_base::result __r;
          streamsize __ilen = 0;

          do
            {
              char* __next;
              __r = _M_codecvt->unshift(_M_state_cur, __buf,
                                        __buf + __blen, __next);
              if (__r == codecvt_base::error)
                __testvalid = false;
              else if (__r == codecvt_base::ok ||
                       __r == codecvt_base::partial)
                {
                  __ilen = __next - __buf;
                  if (__ilen > 0)
                    {
                      const streamsize __elen = _M_file.xsputn(__buf, __ilen);
                      if (__elen != __ilen)
                        __testvalid = false;
                    }
                }
            }
          while (__r == codecvt_base::partial && __ilen > 0 && __testvalid);

          if (__testvalid)
            {
              // This second call to overflow() is required by the standard,
              // but it's not clear why it's needed, since the output buffer
              // should be empty by this point (it should have been emptied
              // in the first call to overflow()).
              const int_type __tmp = this->overflow();
              if (traits_type::eq_int_type(__tmp, traits_type::eof()))
                __testvalid = false;
            }
        }
      return __testvalid;
    }

  template<typename _CharT, typename _Traits>
    int
    basic_filebuf<_CharT, _Traits>::
    sync()
    {
      // Make sure that the internal buffer resyncs its idea of
      // the file position with the external file.
      int __ret = 0;
      if (this->pbase() < this->pptr())
        {
          const int_type __tmp = this->overflow();
          if (traits_type::eq_int_type(__tmp, traits_type::eof()))
            __ret = -1;
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    void
    basic_filebuf<_CharT, _Traits>::
    imbue(const locale& __loc)
    {
      bool __testvalid = true;

      const __codecvt_type* const _M_codecvt_tmp
        = __try_use_facet<__codecvt_type>(__loc);

      if (this->is_open())
        {
          // encoding() == -1 is ok only at the beginning.
          if ((_M_reading || _M_writing)
              && __check_facet(_M_codecvt).encoding() == -1)
            __testvalid = false;
          else
            {
              if (_M_reading)
                {
                  if (__check_facet(_M_codecvt).always_noconv())
                    {
                      if (_M_codecvt_tmp
                          && !__check_facet(_M_codecvt_tmp).always_noconv())
                        __testvalid = this->seekoff(0, ios_base::cur, _M_mode)
                                      != pos_type(off_type(-1));
                    }
                  else
                    {
                      // External position corresponding to gptr().
                      _M_ext_next = _M_ext_buf
                        + _M_codecvt->length(_M_state_last, _M_ext_buf,
                                             _M_ext_next,
                                             this->gptr() - this->eback());
                      const streamsize __remainder = _M_ext_end - _M_ext_next;
                      if (__remainder)
                        __builtin_memmove(_M_ext_buf, _M_ext_next, __remainder);

                      _M_ext_next = _M_ext_buf;
                      _M_ext_end = _M_ext_buf + __remainder;
                      _M_set_buffer(-1);
                      _M_state_last = _M_state_cur = _M_state_beg;
                    }
                }
              else if (_M_writing && (__testvalid = _M_terminate_output()))
                _M_set_buffer(-1);
            }
        }

      if (__testvalid)
        _M_codecvt = _M_codecvt_tmp;
      else
        _M_codecvt = 0;
    }

  // Inhibit implicit instantiations for required instantiations,
  // which are defined via explicit instantiations elsewhere.
#if _GLIBCXX_EXTERN_TEMPLATE
  extern template class basic_filebuf<char>;
  extern template class basic_ifstream<char>;
  extern template class basic_ofstream<char>;
  extern template class basic_fstream<char>;

#ifdef _GLIBCXX_USE_WCHAR_T
  extern template class basic_filebuf<wchar_t>;
  extern template class basic_ifstream<wchar_t>;
  extern template class basic_ofstream<wchar_t>;
  extern template class basic_fstream<wchar_t>;
#endif
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#pragma GCC diagnostic pop
#endif