libstdc++: stdio_filebuf.h Source File

libstdc++

stdio_filebuf.h
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1// File descriptor layer for filebuf -*- C++ -*-
2
3// Copyright (C) 2002-2026 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_filebuf.h
26 * This file is a GNU extension to the Standard C++ Library.
27 */
28
29#ifndef _STDIO_FILEBUF_H
30#define _STDIO_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 <fstream>
39
40namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
41{
42_GLIBCXX_BEGIN_NAMESPACE_VERSION
43
44 /**
45 * @brief Provides a layer of compatibility for C/POSIX.
46 * @ingroup io
47 *
48 * This GNU extension provides extensions for working with standard C
49 * FILE*'s and POSIX file descriptors. It must be instantiated by the
50 * user with the type of character used in the file stream, e.g.,
51 * stdio_filebuf<char>.
52 */
53 template<typename _CharT, typename _Traits = std::char_traits<_CharT> >
54 class stdio_filebuf : public std::basic_filebuf<_CharT, _Traits>
55 {
56 public:
57 // Types:
58 typedef _CharT char_type;
59 typedef _Traits traits_type;
60 typedef typename traits_type::int_type int_type;
61 typedef typename traits_type::pos_type pos_type;
62 typedef typename traits_type::off_type off_type;
63 typedef std::size_t size_t;
64
65 public:
66 /**
67 * deferred initialization
68 */
69 stdio_filebuf() : std::basic_filebuf<_CharT, _Traits>() {}
70
71 /**
72 * @param __fd An open file descriptor.
73 * @param __mode Same meaning as in a standard filebuf.
74 * @param __size Optimal or preferred size of internal buffer,
75 * in chars.
76 *
77 * This constructor associates a file stream buffer with an open
78 * POSIX file descriptor. The file descriptor will be automatically
79 * closed when the stdio_filebuf is closed/destroyed.
80 */
81 stdio_filebuf(int __fd, std::ios_base::openmode __mode,
82 size_t __size = static_cast<size_t>(_GLIBCXX_BUFSIZ));
83
84 /**
85 * @param __f An open @c FILE*.
86 * @param __mode Same meaning as in a standard filebuf.
87 * @param __size Optimal or preferred size of internal buffer,
88 * in chars. Defaults to system's @c BUFSIZ.
89 *
90 * This constructor associates a file stream buffer with an open
91 * C @c FILE*. The @c FILE* will not be automatically closed when the
92 * stdio_filebuf is closed/destroyed.
93 */
94 stdio_filebuf(std::__c_file* __f, std::ios_base::openmode __mode,
95 size_t __size = static_cast<size_t>(_GLIBCXX_BUFSIZ));
96
97 /**
98 * Closes the external data stream if the file descriptor constructor
99 * was used.
100 */
101 virtual
102 ~stdio_filebuf();
103
104#if __cplusplus >= 201103L
105 stdio_filebuf(stdio_filebuf&&) = default;
106 stdio_filebuf& operator=(stdio_filebuf&&) = default;
107
108 void
109 swap(stdio_filebuf& __fb)
110 { std::basic_filebuf<_CharT, _Traits>::swap(__fb); }
111#endif
112
113 /**
114 * @return The underlying file descriptor.
115 *
116 * Once associated with an external data stream, this function can be
117 * used to access the underlying POSIX file descriptor. Note that
118 * there is no way for the library to track what you do with the
119 * descriptor, so be careful.
120 */
121 int
122 fd() { return this->_M_file.fd(); }
123
124 /**
125 * @return The underlying FILE*.
126 *
127 * This function can be used to access the underlying "C" file pointer.
128 * Note that there is no way for the library to track what you do
129 * with the file, so be careful.
130 */
131 std::__c_file*
132 file() { return this->_M_file.file(); }
133 };
134
135 template<typename _CharT, typename _Traits>
136 stdio_filebuf<_CharT, _Traits>::~stdio_filebuf()
137 { }
138
139 template<typename _CharT, typename _Traits>
140 stdio_filebuf<_CharT, _Traits>::
141 stdio_filebuf(int __fd, std::ios_base::openmode __mode, size_t __size)
142 {
143 this->_M_file.sys_open(__fd, __mode);
144 if (this->is_open())
145 {
146 this->_M_mode = __mode;
147 this->_M_buf_size = __size;
148 this->_M_allocate_internal_buffer();
149 this->_M_reading = false;
150 this->_M_writing = false;
151 this->_M_set_buffer(-1);
152 }
153 }
154
155 template<typename _CharT, typename _Traits>
156 stdio_filebuf<_CharT, _Traits>::
157 stdio_filebuf(std::__c_file* __f, std::ios_base::openmode __mode,
158 size_t __size)
159 {
160 this->_M_file.sys_open(__f, __mode);
161 if (this->is_open())
162 {
163 this->_M_mode = __mode;
164 this->_M_buf_size = __size;
165 this->_M_allocate_internal_buffer();
166 this->_M_reading = false;
167 this->_M_writing = false;
168 this->_M_set_buffer(-1);
169 }
170 }
171
172_GLIBCXX_END_NAMESPACE_VERSION
173} // namespace
174
175#endif
fstream
requires_hosted.h
std
ISO C++ entities toplevel namespace is std.
__gnu_cxx
GNU extensions for public use.
std::basic_filebuf
The actual work of input and output (for files).
Definition fstream:93
std::basic_filebuf::_M_mode
ios_base::openmode _M_mode
Place to stash in || out || in | out settings for current filebuf.
Definition fstream:133
std::basic_filebuf::is_open
bool is_open() const
Returns true if the external file is open.
Definition fstream:278
std::basic_filebuf::_M_buf_size
size_t _M_buf_size
Definition fstream:155
std::basic_filebuf::_M_reading
bool _M_reading
Definition fstream:167
std::basic_filebuf::basic_filebuf
basic_filebuf()
Does not open any files.
Definition fstream.tcc:86
std::basic_filebuf::_M_set_buffer
void _M_set_buffer(streamsize __off)
Definition fstream:502
std::ios_base::openmode
_Ios_Openmode openmode
This is a bitmask type.
Definition ios_base.h:484
__gnu_cxx::stdio_filebuf
Provides a layer of compatibility for C/POSIX.
Definition stdio_filebuf.h:55
__gnu_cxx::stdio_filebuf::~stdio_filebuf
virtual ~stdio_filebuf()
Definition stdio_filebuf.h:136
__gnu_cxx::stdio_filebuf::stdio_filebuf
stdio_filebuf()
Definition stdio_filebuf.h:69
__gnu_cxx::stdio_filebuf::file
std::__c_file * file()
Definition stdio_filebuf.h:132
__gnu_cxx::stdio_filebuf::fd
int fd()
Definition stdio_filebuf.h:122