libstdc++
stdio_sync_filebuf.h
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1 // Iostreams wrapper for stdio FILE* -*- C++ -*-
2 
3 // Copyright (C) 2003-2025 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file ext/stdio_sync_filebuf.h
26  * This file is a GNU extension to the Standard C++ Library.
27  */
28 
29 #ifndef _STDIO_SYNC_FILEBUF_H
30 #define _STDIO_SYNC_FILEBUF_H 1
31 
32 #ifdef _GLIBCXX_SYSHDR
33 #pragma GCC system_header
34 #endif
35 
36 #include <bits/requires_hosted.h> // GNU extensions are currently omitted
37 
38 #include <streambuf>
39 #include <cstdio>
40 #include <bits/c++io.h> // For __c_file
41 #include <bits/move.h> // For __exchange
42 
43 #ifdef _GLIBCXX_USE_WCHAR_T
44 #include <cwchar>
45 #endif
46 
47 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
48 {
49 _GLIBCXX_BEGIN_NAMESPACE_VERSION
50 
51  /**
52  * @brief Provides a layer of compatibility for C.
53  * @ingroup io
54  *
55  * This GNU extension provides extensions for working with standard
56  * C FILE*'s. It must be instantiated by the user with the type of
57  * character used in the file stream, e.g., stdio_filebuf<char>.
58  */
59  template<typename _CharT, typename _Traits = std::char_traits<_CharT> >
60  class stdio_sync_filebuf : public std::basic_streambuf<_CharT, _Traits>
61  {
62  public:
63  // Types:
64  typedef _CharT char_type;
65  typedef _Traits traits_type;
66  typedef typename traits_type::int_type int_type;
67  typedef typename traits_type::pos_type pos_type;
68  typedef typename traits_type::off_type off_type;
69 
70  private:
72 
73  // Underlying stdio FILE
74  std::__c_file* _M_file;
75 
76  // Last character gotten. This is used when pbackfail is
77  // called from basic_streambuf::sungetc()
78  int_type _M_unget_buf;
79 
80  public:
81  explicit
82  stdio_sync_filebuf(std::__c_file* __f)
83  : _M_file(__f), _M_unget_buf(traits_type::eof())
84  { }
85 
86 #if __cplusplus >= 201103L
87  stdio_sync_filebuf(stdio_sync_filebuf&& __fb) noexcept
88  : __streambuf_type(std::move(__fb)),
89  _M_file(__fb._M_file), _M_unget_buf(__fb._M_unget_buf)
90  {
91  __fb._M_file = nullptr;
92  __fb._M_unget_buf = traits_type::eof();
93  }
94 
96  operator=(stdio_sync_filebuf&& __fb) noexcept
97  {
98  __streambuf_type::operator=(__fb);
99  _M_file = std::__exchange(__fb._M_file, nullptr);
100  _M_unget_buf = std::__exchange(__fb._M_unget_buf, traits_type::eof());
101  return *this;
102  }
103 
104  void
105  swap(stdio_sync_filebuf& __fb)
106  {
107  __streambuf_type::swap(__fb);
108  std::swap(_M_file, __fb._M_file);
109  std::swap(_M_unget_buf, __fb._M_unget_buf);
110  }
111 #endif
112 
113  /**
114  * @return The underlying FILE*.
115  *
116  * This function can be used to access the underlying C file pointer.
117  * Note that there is no way for the library to track what you do
118  * with the file, so be careful.
119  */
120  std::__c_file*
121  file() { return this->_M_file; }
122 
123  protected:
124  int_type
125  syncgetc();
126 
127  int_type
128  syncungetc(int_type __c);
129 
130  int_type
131  syncputc(int_type __c);
132 
133  virtual int_type
135  {
136  int_type __c = this->syncgetc();
137  return this->syncungetc(__c);
138  }
139 
140  virtual int_type
142  {
143  // Store the gotten character in case we need to unget it.
144  _M_unget_buf = this->syncgetc();
145  return _M_unget_buf;
146  }
147 
148  virtual int_type
149  pbackfail(int_type __c = traits_type::eof())
150  {
151  int_type __ret;
152  const int_type __eof = traits_type::eof();
153 
154  // Check if the unget or putback was requested
155  if (traits_type::eq_int_type(__c, __eof)) // unget
156  {
157  if (!traits_type::eq_int_type(_M_unget_buf, __eof))
158  __ret = this->syncungetc(_M_unget_buf);
159  else // buffer invalid, fail.
160  __ret = __eof;
161  }
162  else // putback
163  __ret = this->syncungetc(__c);
164 
165  // The buffered character is no longer valid, discard it.
166  _M_unget_buf = __eof;
167  return __ret;
168  }
169 
170  virtual std::streamsize
171  xsgetn(char_type* __s, std::streamsize __n);
172 
173  virtual int_type
174  overflow(int_type __c = traits_type::eof())
175  {
176  int_type __ret;
177  if (traits_type::eq_int_type(__c, traits_type::eof()))
178  {
179  if (std::fflush(_M_file))
180  __ret = traits_type::eof();
181  else
182  __ret = traits_type::not_eof(__c);
183  }
184  else
185  __ret = this->syncputc(__c);
186  return __ret;
187  }
188 
189  virtual std::streamsize
190  xsputn(const char_type* __s, std::streamsize __n);
191 
192  virtual int
194  { return std::fflush(_M_file); }
195 
196  virtual std::streampos
197  seekoff(std::streamoff __off, std::ios_base::seekdir __dir,
198  std::ios_base::openmode = std::ios_base::in | std::ios_base::out)
199  {
200  std::streampos __ret(std::streamoff(-1));
201  int __whence;
202  if (__dir == std::ios_base::beg)
203  __whence = SEEK_SET;
204  else if (__dir == std::ios_base::cur)
205  __whence = SEEK_CUR;
206  else
207  __whence = SEEK_END;
208 #ifdef _GLIBCXX_USE_LFS
209  if (!fseeko64(_M_file, __off, __whence))
210  __ret = std::streampos(ftello64(_M_file));
211 #else
212  if (!fseek(_M_file, __off, __whence))
213  __ret = std::streampos(std::ftell(_M_file));
214 #endif
215  return __ret;
216  }
217 
218  virtual std::streampos
220  std::ios_base::openmode __mode =
222  { return seekoff(std::streamoff(__pos), std::ios_base::beg, __mode); }
223  };
224 
225  template<>
226  inline stdio_sync_filebuf<char>::int_type
227  stdio_sync_filebuf<char>::syncgetc()
228  { return std::getc(_M_file); }
229 
230  template<>
231  inline stdio_sync_filebuf<char>::int_type
232  stdio_sync_filebuf<char>::syncungetc(int_type __c)
233  { return std::ungetc(__c, _M_file); }
234 
235  template<>
236  inline stdio_sync_filebuf<char>::int_type
237  stdio_sync_filebuf<char>::syncputc(int_type __c)
238  { return std::putc(__c, _M_file); }
239 
240  template<>
241  inline std::streamsize
242  stdio_sync_filebuf<char>::xsgetn(char* __s, std::streamsize __n)
243  {
244  std::streamsize __ret = std::fread(__s, 1, __n, _M_file);
245  if (__ret > 0)
246  _M_unget_buf = traits_type::to_int_type(__s[__ret - 1]);
247  else
248  _M_unget_buf = traits_type::eof();
249  return __ret;
250  }
251 
252  template<>
253  inline std::streamsize
254  stdio_sync_filebuf<char>::xsputn(const char* __s, std::streamsize __n)
255  { return std::fwrite(__s, 1, __n, _M_file); }
256 
257 #ifdef _GLIBCXX_USE_WCHAR_T
258  template<>
259  inline stdio_sync_filebuf<wchar_t>::int_type
260  stdio_sync_filebuf<wchar_t>::syncgetc()
261  { return std::getwc(_M_file); }
262 
263  template<>
264  inline stdio_sync_filebuf<wchar_t>::int_type
265  stdio_sync_filebuf<wchar_t>::syncungetc(int_type __c)
266  { return std::ungetwc(__c, _M_file); }
267 
268  template<>
269  inline stdio_sync_filebuf<wchar_t>::int_type
270  stdio_sync_filebuf<wchar_t>::syncputc(int_type __c)
271  { return std::putwc(__c, _M_file); }
272 
273  template<>
274  inline std::streamsize
275  stdio_sync_filebuf<wchar_t>::xsgetn(wchar_t* __s, std::streamsize __n)
276  {
277  std::streamsize __ret = 0;
278  const int_type __eof = traits_type::eof();
279  while (__n--)
280  {
281  int_type __c = this->syncgetc();
282  if (traits_type::eq_int_type(__c, __eof))
283  break;
284  __s[__ret] = traits_type::to_char_type(__c);
285  ++__ret;
286  }
287 
288  if (__ret > 0)
289  _M_unget_buf = traits_type::to_int_type(__s[__ret - 1]);
290  else
291  _M_unget_buf = traits_type::eof();
292  return __ret;
293  }
294 
295  template<>
296  inline std::streamsize
297  stdio_sync_filebuf<wchar_t>::xsputn(const wchar_t* __s,
298  std::streamsize __n)
299  {
300  std::streamsize __ret = 0;
301  const int_type __eof = traits_type::eof();
302  while (__n--)
303  {
304  if (traits_type::eq_int_type(this->syncputc(*__s++), __eof))
305  break;
306  ++__ret;
307  }
308  return __ret;
309  }
310 #endif
311 
312 #if _GLIBCXX_EXTERN_TEMPLATE
313 #pragma GCC diagnostic push
314 #pragma GCC diagnostic ignored "-Wc++11-extensions"
315  extern template class stdio_sync_filebuf<char>;
316 #ifdef _GLIBCXX_USE_WCHAR_T
317  extern template class stdio_sync_filebuf<wchar_t>;
318 #endif
319 #pragma GCC diagnostic pop
320 #endif
321 
322 _GLIBCXX_END_NAMESPACE_VERSION
323 } // namespace
324 
325 #endif
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:138
ptrdiff_t streamsize
Integral type for I/O operation counts and buffer sizes.
Definition: postypes.h:73
long long streamoff
Type used by fpos, char_traits<char>, and char_traits<wchar_t>.
Definition: postypes.h:68
fpos< mbstate_t > streampos
File position for char streams.
Definition: postypes.h:209
GNU extensions for public use.
The actual work of input and output (interface).
Definition: streambuf:127
static const seekdir cur
Request a seek relative to the current position within the sequence.
Definition: ios_base.h:529
static const seekdir beg
Request a seek relative to the beginning of the stream.
Definition: ios_base.h:526
static const openmode in
Open for input. Default for ifstream and fstream.
Definition: ios_base.h:498
static const openmode out
Open for output. Default for ofstream and fstream.
Definition: ios_base.h:501
Class representing stream positions.
Definition: postypes.h:88
Provides a layer of compatibility for C.
virtual std::streampos seekpos(std::streampos __pos, std::ios_base::openmode __mode=std::ios_base::in|std::ios_base::out)
Alters the stream positions.
virtual int_type underflow()
Fetches more data from the controlled sequence.
virtual int sync()
Synchronizes the buffer arrays with the controlled sequences.
virtual int_type uflow()
Fetches more data from the controlled sequence.