stdio_sync_filebuf.h

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// Iostreams wrapper for stdio FILE* -*- C++ -*-

// Copyright (C) 2003-2025 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 ext/stdio_sync_filebuf.h
 *  This file is a GNU extension to the Standard C++ Library.
 */

#ifndef _STDIO_SYNC_FILEBUF_H
#define _STDIO_SYNC_FILEBUF_H 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#include <bits/requires_hosted.h> // GNU extensions are currently omitted

#include <streambuf>
#include <cstdio>
#include <bits/c++io.h>  // For __c_file
#include <bits/move.h>   // For __exchange

#ifdef _GLIBCXX_USE_WCHAR_T
#include <cwchar>
#endif

namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   *  @brief Provides a layer of compatibility for C.
   *  @ingroup io
   *
   *  This GNU extension provides extensions for working with standard
   *  C FILE*'s.  It must be instantiated by the user with the type of
   *  character used in the file stream, e.g., stdio_filebuf<char>.
  */
  template<typename _CharT, typename _Traits = std::char_traits<_CharT> >
    class stdio_sync_filebuf : public std::basic_streambuf<_CharT, _Traits>
    {
    public:
      // Types:
      typedef _CharT                                    char_type;
      typedef _Traits                                   traits_type;
      typedef typename traits_type::int_type            int_type;
      typedef typename traits_type::pos_type            pos_type;
      typedef typename traits_type::off_type            off_type;

    private:
      typedef std::basic_streambuf<_CharT, _Traits> __streambuf_type;

      // Underlying stdio FILE
      std::__c_file* _M_file;

      // Last character gotten. This is used when pbackfail is
      // called from basic_streambuf::sungetc()
      int_type _M_unget_buf;

    public:
      explicit
      stdio_sync_filebuf(std::__c_file* __f)
      : _M_file(__f), _M_unget_buf(traits_type::eof())
      { }

#if __cplusplus >= 201103L
      stdio_sync_filebuf(stdio_sync_filebuf&& __fb) noexcept
      : __streambuf_type(std::move(__fb)),
      _M_file(__fb._M_file), _M_unget_buf(__fb._M_unget_buf)
      {
        __fb._M_file = nullptr;
        __fb._M_unget_buf = traits_type::eof();
      }

      stdio_sync_filebuf&
      operator=(stdio_sync_filebuf&& __fb) noexcept
      {
        __streambuf_type::operator=(__fb);
        _M_file = std::__exchange(__fb._M_file, nullptr);
        _M_unget_buf = std::__exchange(__fb._M_unget_buf, traits_type::eof());
        return *this;
      }

      void
      swap(stdio_sync_filebuf& __fb)
      {
        __streambuf_type::swap(__fb);
        std::swap(_M_file, __fb._M_file);
        std::swap(_M_unget_buf, __fb._M_unget_buf);
      }
#endif

      /**
       *  @return  The underlying FILE*.
       *
       *  This function can be used to access the underlying C file pointer.
       *  Note that there is no way for the library to track what you do
       *  with the file, so be careful.
       */
      std::__c_file*
      file() { return this->_M_file; }

    protected:
      int_type
      syncgetc();

      int_type
      syncungetc(int_type __c);

      int_type
      syncputc(int_type __c);

      virtual int_type
      underflow()
      {
        int_type __c = this->syncgetc();
        return this->syncungetc(__c);
      }

      virtual int_type
      uflow()
      {
        // Store the gotten character in case we need to unget it.
        _M_unget_buf = this->syncgetc();
        return _M_unget_buf;
      }

      virtual int_type
      pbackfail(int_type __c = traits_type::eof())
      {
        int_type __ret;
        const int_type __eof = traits_type::eof();

        // Check if the unget or putback was requested
        if (traits_type::eq_int_type(__c, __eof)) // unget
          {
            if (!traits_type::eq_int_type(_M_unget_buf, __eof))
              __ret = this->syncungetc(_M_unget_buf);
            else // buffer invalid, fail.
              __ret = __eof;
          }
        else // putback
          __ret = this->syncungetc(__c);

        // The buffered character is no longer valid, discard it.
        _M_unget_buf = __eof;
        return __ret;
      }

      virtual std::streamsize
      xsgetn(char_type* __s, std::streamsize __n);

      virtual int_type
      overflow(int_type __c = traits_type::eof())
      {
        int_type __ret;
        if (traits_type::eq_int_type(__c, traits_type::eof()))
          {
            if (std::fflush(_M_file))
              __ret = traits_type::eof();
            else
              __ret = traits_type::not_eof(__c);
          }
        else
          __ret = this->syncputc(__c);
        return __ret;
      }

      virtual std::streamsize
      xsputn(const char_type* __s, std::streamsize __n);

      virtual int
      sync()
      { return std::fflush(_M_file); }

      virtual std::streampos
      seekoff(std::streamoff __off, std::ios_base::seekdir __dir,
              std::ios_base::openmode = std::ios_base::in | std::ios_base::out)
      {
        std::streampos __ret(std::streamoff(-1));
        int __whence;
        if (__dir == std::ios_base::beg)
          __whence = SEEK_SET;
        else if (__dir == std::ios_base::cur)
          __whence = SEEK_CUR;
        else
          __whence = SEEK_END;
#ifdef _GLIBCXX_USE_LFS
        if (!fseeko64(_M_file, __off, __whence))
          __ret = std::streampos(ftello64(_M_file));
#else
        if (!fseek(_M_file, __off, __whence))
          __ret = std::streampos(std::ftell(_M_file));
#endif
        return __ret;
      }

      virtual std::streampos
      seekpos(std::streampos __pos,
              std::ios_base::openmode __mode =
              std::ios_base::in | std::ios_base::out)
      { return seekoff(std::streamoff(__pos), std::ios_base::beg, __mode); }
    };

  template<>
    inline stdio_sync_filebuf<char>::int_type
    stdio_sync_filebuf<char>::syncgetc()
    { return std::getc(_M_file); }

  template<>
    inline stdio_sync_filebuf<char>::int_type
    stdio_sync_filebuf<char>::syncungetc(int_type __c)
    { return std::ungetc(__c, _M_file); }

  template<>
    inline stdio_sync_filebuf<char>::int_type
    stdio_sync_filebuf<char>::syncputc(int_type __c)
    { return std::putc(__c, _M_file); }

  template<>
    inline std::streamsize
    stdio_sync_filebuf<char>::xsgetn(char* __s, std::streamsize __n)
    {
      std::streamsize __ret = std::fread(__s, 1, __n, _M_file);
      if (__ret > 0)
        _M_unget_buf = traits_type::to_int_type(__s[__ret - 1]);
      else
        _M_unget_buf = traits_type::eof();
      return __ret;
    }

  template<>
    inline std::streamsize
    stdio_sync_filebuf<char>::xsputn(const char* __s, std::streamsize __n)
    { return std::fwrite(__s, 1, __n, _M_file); }

#ifdef _GLIBCXX_USE_WCHAR_T
  template<>
    inline stdio_sync_filebuf<wchar_t>::int_type
    stdio_sync_filebuf<wchar_t>::syncgetc()
    { return std::getwc(_M_file); }

  template<>
    inline stdio_sync_filebuf<wchar_t>::int_type
    stdio_sync_filebuf<wchar_t>::syncungetc(int_type __c)
    { return std::ungetwc(__c, _M_file); }

  template<>
    inline stdio_sync_filebuf<wchar_t>::int_type
    stdio_sync_filebuf<wchar_t>::syncputc(int_type __c)
    { return std::putwc(__c, _M_file); }

  template<>
    inline std::streamsize
    stdio_sync_filebuf<wchar_t>::xsgetn(wchar_t* __s, std::streamsize __n)
    {
      std::streamsize __ret = 0;
      const int_type __eof = traits_type::eof();
      while (__n--)
        {
          int_type __c = this->syncgetc();
          if (traits_type::eq_int_type(__c, __eof))
            break;
          __s[__ret] = traits_type::to_char_type(__c);
          ++__ret;
        }

      if (__ret > 0)
        _M_unget_buf = traits_type::to_int_type(__s[__ret - 1]);
      else
        _M_unget_buf = traits_type::eof();
      return __ret;
    }

  template<>
    inline std::streamsize
    stdio_sync_filebuf<wchar_t>::xsputn(const wchar_t* __s,
                                        std::streamsize __n)
    {
      std::streamsize __ret = 0;
      const int_type __eof = traits_type::eof();
      while (__n--)
        {
          if (traits_type::eq_int_type(this->syncputc(*__s++), __eof))
            break;
          ++__ret;
        }
      return __ret;
    }
#endif

#if _GLIBCXX_EXTERN_TEMPLATE
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++11-extensions"
  extern template class stdio_sync_filebuf<char>;
#ifdef _GLIBCXX_USE_WCHAR_T
  extern template class stdio_sync_filebuf<wchar_t>;
#endif
#pragma GCC diagnostic pop
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif