fstream.tcc

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

// Copyright (C) 1997-2014 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

#pragma GCC system_header

#include <bits/cxxabi_forced.h>

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(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)
    {
      if (has_facet<__codecvt_type>(this->_M_buf_locale))
   _M_codecvt = &use_facet<__codecvt_type>(this->_M_buf_locale);
    }

  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;
    }

  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(__cxxabiv1::__forced_unwind&)
     {
       _M_file.close();
       __throw_exception_again;
     }
   __catch(...)
     { __testfail = true; }
      }

      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"));
   }
      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"));
          if (__len == 0)
        break;
 
          __n -= __len;
          __ret += __len;
          if (__n == 0)
        break;
 
          __s += __len;
        }
 
      if (__n == 0)
        {
          _M_set_buffer(0);
          _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 sufficiently large 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)
   {
     // Measurement would reveal the best choice.
     const streamsize __chunk = 1ul << 10;
     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;

     const streamsize __limit = std::min(__chunk, __bufavail);
     if (__n >= __limit)
       {
         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* _M_codecvt_tmp = 0;
      if (__builtin_expect(has_facet<__codecvt_type>(__loc), true))
   _M_codecvt_tmp = &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

#endif