fstream.tcc

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

// Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
// 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 2, 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.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

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

#ifndef _FSTREAM_TCC
#define _FSTREAM_TCC 1

#pragma GCC system_header

namespace std
{
  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 && !this->_M_buf)
    {
      this->_M_buf = new char_type[this->_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 [] this->_M_buf;
      this->_M_buf = NULL;
      _M_buf_allocated = false;
    }
      delete [] _M_ext_buf;
      _M_ext_buf = NULL;
      _M_ext_buf_size = 0;
      _M_ext_next = NULL;
      _M_ext_end = NULL;
    }

  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(NULL), _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 = NULL;
      if (!this->is_open())
    {
      _M_file.open(__s, __mode);
      if (this->is_open())
        {
          _M_allocate_internal_buffer();
          this->_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() throw()
    {
      __filebuf_type* __ret = NULL;
      if (this->is_open())
    {
      bool __testfail = false;
      try
        {
          if (!_M_terminate_output())
        __testfail = true;
        }
      catch(...)
        { __testfail = true; }

      // NB: Do this here so that re-opened filebufs will be cool...
      this->_M_mode = ios_base::openmode(0);
      this->_M_pback_init = false;
      _M_destroy_internal_buffer();
      _M_reading = false;
      _M_writing = false;
      _M_set_buffer(-1);
      _M_state_last = _M_state_cur = _M_state_beg;

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

      if (!__testfail)
        __ret = this;
    }
      return __ret;
    }

  template<typename _CharT, typename _Traits>
    streamsize
    basic_filebuf<_CharT, _Traits>::
    showmanyc()
    {
      streamsize __ret = -1;
      const bool __testin = this->_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 (__check_facet(_M_codecvt).encoding() >= 0)
        __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 = this->_M_mode & ios_base::in;
      if (__testin && !_M_writing)
    {
      // Check for pback madness, and if so swich 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 = this->_M_buf_size > 1
                              ? this->_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)
            std::memcpy(__buf, _M_ext_next, __remainder);

          delete [] _M_ext_buf;
          _M_ext_buf = __buf;
          _M_ext_buf_size = __blen;
        }
          else if (__remainder)
        std::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;
          __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 = this->_M_mode & ios_base::in;
      if (__testin && !_M_writing)
    {
      // Remember whether the pback buffer is active, otherwise below
      // we may try to store in it a second char (libstdc++/9761).
      const bool __testpb = this->_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 = this->_M_mode & ios_base::out;
      if (__testout && !_M_reading)
    {
      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 (this->_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 (this->_M_pback_init)
     {
       if (__n > 0 && this->gptr() == this->eback())
         {
           *__s++ = *this->gptr();
           this->gbump(1);
           __ret = 1;
           --__n;
         }
       _M_destroy_pback();
     }
       
       // 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 = this->_M_mode & ios_base::in;
       const streamsize __buflen = this->_M_buf_size > 1 ? this->_M_buf_size - 1
                                                     : 1;
       if (__n > __buflen && __check_facet(_M_codecvt).always_noconv()
       && __testin && !_M_writing)
     {
       // First, copy the chars already present in the buffer.
       const streamsize __avail = this->egptr() - this->gptr();
       if (__avail != 0)
         {
           if (__avail == 1)
         *__s = *this->gptr();
           else
         traits_type::copy(__s, this->gptr(), __avail);
           __s += __avail;
           this->gbump(__avail);
           __ret += __avail;
           __n -= __avail;
         }

       const streamsize __len = _M_file.xsgetn(reinterpret_cast<char*>(__s),
                           __n);
       if (__len == -1)
         __throw_ios_failure(__N("basic_filebuf::xsgetn "
                     "error reading the file"));
       __ret += __len;
       if (__len == __n)
         {
           _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)
     {
       // 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.
       streamsize __ret = 0;
       const bool __testout = this->_M_mode & ios_base::out;
       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 && this->_M_buf_size > 1)
        __bufavail = this->_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)
      this->_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.
        this->_M_buf = __s;
        this->_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)
    {
      // Ditch any pback buffers to avoid confusion.
      _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)
        {
          if (_M_codecvt->always_noconv())
        __computed_off += this->gptr() - this->egptr();
          else
        {
          // Calculate offset from _M_ext_buf that corresponds
          // to gptr(). Note: uses _M_state_last, which
          // corresponds to eback().
          const int __gptr_off =
            _M_codecvt->length(_M_state_last, _M_ext_buf, _M_ext_next,
                       this->gptr() - this->eback());
          __computed_off += _M_ext_buf + __gptr_off - _M_ext_end;

          // _M_state_last is modified by codecvt::length() so
          // it now corresponds to gptr().
          __state = _M_state_last;
        }
        }
      __ret = _M_seek(__computed_off, __way, __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())
    {
      // Returns pos_type(off_type(-1)) in case of failure.
      __ret = pos_type(_M_file.seekoff(__off, __way));
      _M_reading = false;
      _M_writing = false;
      _M_ext_next = _M_ext_end = _M_ext_buf;
      _M_set_buffer(-1);
      _M_state_cur = __state;
      __ret.state(_M_state_cur);
    }
      return __ret;
    }

  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, this->_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)
            std::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.
  // NB:  This syntax is a GNU extension.
#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
} // namespace std

#endif

---