1// Stream buffer classes -*- C++ -*-
3// Copyright (C) 1997-2021 Free Software Foundation, Inc.
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)
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.
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.
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/>.
25/** @file include/streambuf
26 * This is a Standard C++ Library header.
30// ISO C++ 14882: 27.5 Stream buffers
33#ifndef _GLIBXX_STREAMBUF
34#define _GLIBXX_STREAMBUF 1
36#pragma GCC system_header
38#include <bits/c++config.h>
40#include <bits/localefwd.h>
41#include <bits/ios_base.h>
42#include <bits/cpp_type_traits.h>
43#include <ext/type_traits.h>
45namespace std _GLIBCXX_VISIBILITY(default)
47_GLIBCXX_BEGIN_NAMESPACE_VERSION
49#define _IsUnused __attribute__ ((__unused__))
51 template<typename _CharT, typename _Traits>
53 __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
54 basic_streambuf<_CharT, _Traits>*, bool&);
57 * @brief The actual work of input and output (interface).
60 * @tparam _CharT Type of character stream.
61 * @tparam _Traits Traits for character type, defaults to
62 * char_traits<_CharT>.
64 * This is a base class. Derived stream buffers each control a
65 * pair of character sequences: one for input, and one for output.
67 * Section [27.5.1] of the standard describes the requirements and
68 * behavior of stream buffer classes. That section (three paragraphs)
69 * is reproduced here, for simplicity and accuracy.
71 * -# Stream buffers can impose various constraints on the sequences
72 * they control. Some constraints are:
73 * - The controlled input sequence can be not readable.
74 * - The controlled output sequence can be not writable.
75 * - The controlled sequences can be associated with the contents of
76 * other representations for character sequences, such as external
78 * - The controlled sequences can support operations @e directly to or
79 * from associated sequences.
80 * - The controlled sequences can impose limitations on how the
81 * program can read characters from a sequence, write characters to
82 * a sequence, put characters back into an input sequence, or alter
83 * the stream position.
85 * -# Each sequence is characterized by three pointers which, if non-null,
86 * all point into the same @c charT array object. The array object
87 * represents, at any moment, a (sub)sequence of characters from the
88 * sequence. Operations performed on a sequence alter the values
89 * stored in these pointers, perform reads and writes directly to or
90 * from associated sequences, and alter <em>the stream position</em> and
91 * conversion state as needed to maintain this subsequence relationship.
92 * The three pointers are:
93 * - the <em>beginning pointer</em>, or lowest element address in the
94 * array (called @e xbeg here);
95 * - the <em>next pointer</em>, or next element address that is a
96 * current candidate for reading or writing (called @e xnext here);
97 * - the <em>end pointer</em>, or first element address beyond the
98 * end of the array (called @e xend here).
100 * -# The following semantic constraints shall always apply for any set
101 * of three pointers for a sequence, using the pointer names given
103 * - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
104 * also be non-null pointers into the same @c charT array, as
105 * described above; otherwise, @e xbeg and @e xend shall also be null.
106 * - If @e xnext is not a null pointer and @e xnext < @e xend for an
107 * output sequence, then a <em>write position</em> is available.
108 * In this case, @e *xnext shall be assignable as the next element
109 * to write (to put, or to store a character value, into the sequence).
110 * - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
111 * input sequence, then a <em>putback position</em> is available.
112 * In this case, @e xnext[-1] shall have a defined value and is the
113 * next (preceding) element to store a character that is put back
114 * into the input sequence.
115 * - If @e xnext is not a null pointer and @e xnext< @e xend for an
116 * input sequence, then a <em>read position</em> is available.
117 * In this case, @e *xnext shall have a defined value and is the
118 * next element to read (to get, or to obtain a character value,
119 * from the sequence).
121 template<typename _CharT, typename _Traits>
122 class basic_streambuf
127 * These are standard types. They permit a standardized way of
128 * referring to names of (or names dependent on) the template
129 * parameters, which are specific to the implementation.
131 typedef _CharT char_type;
132 typedef _Traits traits_type;
133 typedef typename traits_type::int_type int_type;
134 typedef typename traits_type::pos_type pos_type;
135 typedef typename traits_type::off_type off_type;
139 /// This is a non-standard type.
140 typedef basic_streambuf<char_type, traits_type> __streambuf_type;
143 friend class basic_ios<char_type, traits_type>;
144 friend class basic_istream<char_type, traits_type>;
145 friend class basic_ostream<char_type, traits_type>;
146 friend class istreambuf_iterator<char_type, traits_type>;
147 friend class ostreambuf_iterator<char_type, traits_type>;
150 __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&);
152 template<bool _IsMove, typename _CharT2>
153 friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
155 __copy_move_a2(istreambuf_iterator<_CharT2>,
156 istreambuf_iterator<_CharT2>, _CharT2*);
158 template<typename _CharT2>
159 friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
160 istreambuf_iterator<_CharT2> >::__type
161 find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
164 template<typename _CharT2, typename _Distance>
165 friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
167 advance(istreambuf_iterator<_CharT2>&, _Distance);
169 friend void __istream_extract(istream&, char*, streamsize);
171 template<typename _CharT2, typename _Traits2, typename _Alloc>
172 friend basic_istream<_CharT2, _Traits2>&
173 operator>>(basic_istream<_CharT2, _Traits2>&,
174 basic_string<_CharT2, _Traits2, _Alloc>&);
176 template<typename _CharT2, typename _Traits2, typename _Alloc>
177 friend basic_istream<_CharT2, _Traits2>&
178 getline(basic_istream<_CharT2, _Traits2>&,
179 basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
183 * This is based on _IO_FILE, just reordered to be more consistent,
184 * and is intended to be the most minimal abstraction for an
186 * - get == input == read
187 * - put == output == write
189 char_type* _M_in_beg; ///< Start of get area.
190 char_type* _M_in_cur; ///< Current read area.
191 char_type* _M_in_end; ///< End of get area.
192 char_type* _M_out_beg; ///< Start of put area.
193 char_type* _M_out_cur; ///< Current put area.
194 char_type* _M_out_end; ///< End of put area.
196 /// Current locale setting.
197 locale _M_buf_locale;
200 /// Destructor deallocates no buffer space.
205 // [27.5.2.2.1] locales
207 * @brief Entry point for imbue().
208 * @param __loc The new locale.
209 * @return The previous locale.
211 * Calls the derived imbue(__loc).
214 pubimbue(const locale& __loc)
216 locale __tmp(this->getloc());
218 _M_buf_locale = __loc;
223 * @brief Locale access.
224 * @return The current locale in effect.
226 * If pubimbue(loc) has been called, then the most recent @c loc
227 * is returned. Otherwise the global locale in effect at the time
228 * of construction is returned.
232 { return _M_buf_locale; }
234 // [27.5.2.2.2] buffer management and positioning
237 * @brief Entry points for derived buffer functions.
239 * The public versions of @c pubfoo dispatch to the protected
240 * derived @c foo member functions, passing the arguments (if any)
241 * and returning the result unchanged.
244 pubsetbuf(char_type* __s, streamsize __n)
245 { return this->setbuf(__s, __n); }
248 * @brief Alters the stream position.
249 * @param __off Offset.
250 * @param __way Value for ios_base::seekdir.
251 * @param __mode Value for ios_base::openmode.
253 * Calls virtual seekoff function.
256 pubseekoff(off_type __off, ios_base::seekdir __way,
257 ios_base::openmode __mode = ios_base::in | ios_base::out)
258 { return this->seekoff(__off, __way, __mode); }
261 * @brief Alters the stream position.
262 * @param __sp Position
263 * @param __mode Value for ios_base::openmode.
265 * Calls virtual seekpos function.
268 pubseekpos(pos_type __sp,
269 ios_base::openmode __mode = ios_base::in | ios_base::out)
270 { return this->seekpos(__sp, __mode); }
273 * @brief Calls virtual sync function.
276 pubsync() { return this->sync(); }
279 // [27.5.2.2.3] get area
281 * @brief Looking ahead into the stream.
282 * @return The number of characters available.
284 * If a read position is available, returns the number of characters
285 * available for reading before the buffer must be refilled.
286 * Otherwise returns the derived @c showmanyc().
291 const streamsize __ret = this->egptr() - this->gptr();
292 return __ret ? __ret : this->showmanyc();
296 * @brief Getting the next character.
297 * @return The next character, or eof.
299 * Calls @c sbumpc(), and if that function returns
300 * @c traits::eof(), so does this function. Otherwise, @c sgetc().
305 int_type __ret = traits_type::eof();
306 if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(),
308 __ret = this->sgetc();
313 * @brief Getting the next character.
314 * @return The next character, or eof.
316 * If the input read position is available, returns that character
317 * and increments the read pointer, otherwise calls and returns
324 if (__builtin_expect(this->gptr() < this->egptr(), true))
326 __ret = traits_type::to_int_type(*this->gptr());
330 __ret = this->uflow();
335 * @brief Getting the next character.
336 * @return The next character, or eof.
338 * If the input read position is available, returns that character,
339 * otherwise calls and returns @c underflow(). Does not move the
340 * read position after fetching the character.
346 if (__builtin_expect(this->gptr() < this->egptr(), true))
347 __ret = traits_type::to_int_type(*this->gptr());
349 __ret = this->underflow();
354 * @brief Entry point for xsgetn.
355 * @param __s A buffer area.
356 * @param __n A count.
358 * Returns xsgetn(__s,__n). The effect is to fill @a __s[0] through
359 * @a __s[__n-1] with characters from the input sequence, if possible.
362 sgetn(char_type* __s, streamsize __n)
363 { return this->xsgetn(__s, __n); }
365 // [27.5.2.2.4] putback
367 * @brief Pushing characters back into the input stream.
368 * @param __c The character to push back.
369 * @return The previous character, if possible.
371 * Similar to sungetc(), but @a __c is pushed onto the stream
372 * instead of <em>the previous character.</em> If successful,
373 * the next character fetched from the input stream will be @a
377 sputbackc(char_type __c)
380 const bool __testpos = this->eback() < this->gptr();
381 if (__builtin_expect(!__testpos ||
382 !traits_type::eq(__c, this->gptr()[-1]), false))
383 __ret = this->pbackfail(traits_type::to_int_type(__c));
387 __ret = traits_type::to_int_type(*this->gptr());
393 * @brief Moving backwards in the input stream.
394 * @return The previous character, if possible.
396 * If a putback position is available, this function decrements
397 * the input pointer and returns that character. Otherwise,
398 * calls and returns pbackfail(). The effect is to @a unget
399 * the last character @a gotten.
405 if (__builtin_expect(this->eback() < this->gptr(), true))
408 __ret = traits_type::to_int_type(*this->gptr());
411 __ret = this->pbackfail();
415 // [27.5.2.2.5] put area
417 * @brief Entry point for all single-character output functions.
418 * @param __c A character to output.
419 * @return @a __c, if possible.
421 * One of two public output functions.
423 * If a write position is available for the output sequence (i.e.,
424 * the buffer is not full), stores @a __c in that position, increments
425 * the position, and returns @c traits::to_int_type(__c). If a write
426 * position is not available, returns @c overflow(__c).
432 if (__builtin_expect(this->pptr() < this->epptr(), true))
436 __ret = traits_type::to_int_type(__c);
439 __ret = this->overflow(traits_type::to_int_type(__c));
444 * @brief Entry point for all single-character output functions.
445 * @param __s A buffer read area.
446 * @param __n A count.
448 * One of two public output functions.
451 * Returns xsputn(__s,__n). The effect is to write @a __s[0] through
452 * @a __s[__n-1] to the output sequence, if possible.
455 sputn(const char_type* __s, streamsize __n)
456 { return this->xsputn(__s, __n); }
460 * @brief Base constructor.
462 * Only called from derived constructors, and sets up all the
463 * buffer data to zero, including the pointers described in the
464 * basic_streambuf class description. Note that, as a result,
465 * - the class starts with no read nor write positions available,
466 * - this is not an error
469 : _M_in_beg(0), _M_in_cur(0), _M_in_end(0),
470 _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
471 _M_buf_locale(locale())
474 // [27.5.2.3.1] get area access
477 * @brief Access to the get area.
479 * These functions are only available to other protected functions,
480 * including derived classes.
482 * - eback() returns the beginning pointer for the input sequence
483 * - gptr() returns the next pointer for the input sequence
484 * - egptr() returns the end pointer for the input sequence
487 eback() const { return _M_in_beg; }
490 gptr() const { return _M_in_cur; }
493 egptr() const { return _M_in_end; }
497 * @brief Moving the read position.
498 * @param __n The delta by which to move.
500 * This just advances the read position without returning any data.
503 gbump(int __n) { _M_in_cur += __n; }
506 * @brief Setting the three read area pointers.
507 * @param __gbeg A pointer.
508 * @param __gnext A pointer.
509 * @param __gend A pointer.
510 * @post @a __gbeg == @c eback(), @a __gnext == @c gptr(), and
511 * @a __gend == @c egptr()
514 setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
521 // [27.5.2.3.2] put area access
524 * @brief Access to the put area.
526 * These functions are only available to other protected functions,
527 * including derived classes.
529 * - pbase() returns the beginning pointer for the output sequence
530 * - pptr() returns the next pointer for the output sequence
531 * - epptr() returns the end pointer for the output sequence
534 pbase() const { return _M_out_beg; }
537 pptr() const { return _M_out_cur; }
540 epptr() const { return _M_out_end; }
544 * @brief Moving the write position.
545 * @param __n The delta by which to move.
547 * This just advances the write position without returning any data.
550 pbump(int __n) { _M_out_cur += __n; }
553 * @brief Setting the three write area pointers.
554 * @param __pbeg A pointer.
555 * @param __pend A pointer.
556 * @post @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and
557 * @a __pend == @c epptr()
560 setp(char_type* __pbeg, char_type* __pend)
562 _M_out_beg = _M_out_cur = __pbeg;
566 // [27.5.2.4] virtual functions
567 // [27.5.2.4.1] locales
569 * @brief Changes translations.
570 * @param __loc A new locale.
572 * Translations done during I/O which depend on the current
573 * locale are changed by this call. The standard adds,
574 * <em>Between invocations of this function a class derived
575 * from streambuf can safely cache results of calls to locale
576 * functions and to members of facets so obtained.</em>
578 * @note Base class version does nothing.
581 imbue(const locale& __loc _IsUnused)
584 // [27.5.2.4.2] buffer management and positioning
586 * @brief Manipulates the buffer.
588 * Each derived class provides its own appropriate behavior. See
589 * the next-to-last paragraph of
590 * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
591 * for more on this function.
593 * @note Base class version does nothing, returns @c this.
595 virtual basic_streambuf<char_type,_Traits>*
596 setbuf(char_type*, streamsize)
600 * @brief Alters the stream positions.
602 * Each derived class provides its own appropriate behavior.
603 * @note Base class version does nothing, returns a @c pos_type
604 * that represents an invalid stream position.
607 seekoff(off_type, ios_base::seekdir,
608 ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
609 { return pos_type(off_type(-1)); }
612 * @brief Alters the stream positions.
614 * Each derived class provides its own appropriate behavior.
615 * @note Base class version does nothing, returns a @c pos_type
616 * that represents an invalid stream position.
620 ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
621 { return pos_type(off_type(-1)); }
624 * @brief Synchronizes the buffer arrays with the controlled sequences.
625 * @return -1 on failure.
627 * Each derived class provides its own appropriate behavior,
628 * including the definition of @a failure.
629 * @note Base class version does nothing, returns zero.
634 // [27.5.2.4.3] get area
636 * @brief Investigating the data available.
637 * @return An estimate of the number of characters available in the
638 * input sequence, or -1.
640 * <em>If it returns a positive value, then successive calls to
641 * @c underflow() will not return @c traits::eof() until at
642 * least that number of characters have been supplied. If @c
643 * showmanyc() returns -1, then calls to @c underflow() or @c
644 * uflow() will fail.</em> [27.5.2.4.3]/1
646 * @note Base class version does nothing, returns zero.
647 * @note The standard adds that <em>the intention is not only that the
648 * calls [to underflow or uflow] will not return @c eof() but
649 * that they will return immediately.</em>
650 * @note The standard adds that <em>the morphemes of @c showmanyc are
651 * @b es-how-many-see, not @b show-manic.</em>
654 showmanyc() { return 0; }
657 * @brief Multiple character extraction.
658 * @param __s A buffer area.
659 * @param __n Maximum number of characters to assign.
660 * @return The number of characters assigned.
662 * Fills @a __s[0] through @a __s[__n-1] with characters from the input
663 * sequence, as if by @c sbumpc(). Stops when either @a __n characters
664 * have been copied, or when @c traits::eof() would be copied.
666 * It is expected that derived classes provide a more efficient
667 * implementation by overriding this definition.
670 xsgetn(char_type* __s, streamsize __n);
673 * @brief Fetches more data from the controlled sequence.
674 * @return The first character from the <em>pending sequence</em>.
676 * Informally, this function is called when the input buffer is
677 * exhausted (or does not exist, as buffering need not actually be
678 * done). If a buffer exists, it is @a refilled. In either case, the
679 * next available character is returned, or @c traits::eof() to
680 * indicate a null pending sequence.
682 * For a formal definition of the pending sequence, see a good text
683 * such as Langer & Kreft, or [27.5.2.4.3]/7-14.
685 * A functioning input streambuf can be created by overriding only
686 * this function (no buffer area will be used). For an example, see
687 * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html
689 * @note Base class version does nothing, returns eof().
693 { return traits_type::eof(); }
696 * @brief Fetches more data from the controlled sequence.
697 * @return The first character from the <em>pending sequence</em>.
699 * Informally, this function does the same thing as @c underflow(),
700 * and in fact is required to call that function. It also returns
701 * the new character, like @c underflow() does. However, this
702 * function also moves the read position forward by one.
707 int_type __ret = traits_type::eof();
708 const bool __testeof = traits_type::eq_int_type(this->underflow(),
712 __ret = traits_type::to_int_type(*this->gptr());
718 // [27.5.2.4.4] putback
720 * @brief Tries to back up the input sequence.
721 * @param __c The character to be inserted back into the sequence.
722 * @return eof() on failure, <em>some other value</em> on success
723 * @post The constraints of @c gptr(), @c eback(), and @c pptr()
724 * are the same as for @c underflow().
726 * @note Base class version does nothing, returns eof().
729 pbackfail(int_type __c _IsUnused = traits_type::eof())
730 { return traits_type::eof(); }
734 * @brief Multiple character insertion.
735 * @param __s A buffer area.
736 * @param __n Maximum number of characters to write.
737 * @return The number of characters written.
739 * Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if
740 * by @c sputc(). Stops when either @a n characters have been
741 * copied, or when @c sputc() would return @c traits::eof().
743 * It is expected that derived classes provide a more efficient
744 * implementation by overriding this definition.
747 xsputn(const char_type* __s, streamsize __n);
750 * @brief Consumes data from the buffer; writes to the
751 * controlled sequence.
752 * @param __c An additional character to consume.
753 * @return eof() to indicate failure, something else (usually
754 * @a __c, or not_eof())
756 * Informally, this function is called when the output buffer
757 * is full (or does not exist, as buffering need not actually
758 * be done). If a buffer exists, it is @a consumed, with
759 * <em>some effect</em> on the controlled sequence.
760 * (Typically, the buffer is written out to the sequence
761 * verbatim.) In either case, the character @a c is also
762 * written out, if @a __c is not @c eof().
764 * For a formal definition of this function, see a good text
765 * such as Langer & Kreft, or [27.5.2.4.5]/3-7.
767 * A functioning output streambuf can be created by overriding only
768 * this function (no buffer area will be used).
770 * @note Base class version does nothing, returns eof().
773 overflow(int_type __c _IsUnused = traits_type::eof())
774 { return traits_type::eof(); }
776#if _GLIBCXX_USE_DEPRECATED && __cplusplus <= 201402L
777 // Annex D.6 (removed in C++17)
780 * @brief Tosses a character.
782 * Advances the read pointer, ignoring the character that would have
785 * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
787 _GLIBCXX_DEPRECATED_SUGGEST("std::basic_streambuf::sbumpc")
791 if (this->gptr() < this->egptr())
798 // Also used by specializations for char and wchar_t in src.
800 __safe_gbump(streamsize __n) { _M_in_cur += __n; }
803 __safe_pbump(streamsize __n) { _M_out_cur += __n; }
805#if __cplusplus < 201103L
810 basic_streambuf(const basic_streambuf&);
813 operator=(const basic_streambuf&);
815#if __cplusplus >= 201103L
817 swap(basic_streambuf& __sb)
819 std::swap(_M_in_beg, __sb._M_in_beg);
820 std::swap(_M_in_cur, __sb._M_in_cur);
821 std::swap(_M_in_end, __sb._M_in_end);
822 std::swap(_M_out_beg, __sb._M_out_beg);
823 std::swap(_M_out_cur, __sb._M_out_cur);
824 std::swap(_M_out_end, __sb._M_out_end);
825 std::swap(_M_buf_locale, __sb._M_buf_locale);
830#if __cplusplus >= 201103L
831 template<typename _CharT, typename _Traits>
832 std::basic_streambuf<_CharT, _Traits>::
833 basic_streambuf(const basic_streambuf&) = default;
835 template<typename _CharT, typename _Traits>
836 std::basic_streambuf<_CharT, _Traits>&
837 std::basic_streambuf<_CharT, _Traits>::
838 operator=(const basic_streambuf&) = default;
841 // Explicit specialization declarations, defined in src/streambuf.cc.
844 __copy_streambufs_eof(basic_streambuf<char>* __sbin,
845 basic_streambuf<char>* __sbout, bool& __ineof);
846#ifdef _GLIBCXX_USE_WCHAR_T
849 __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
850 basic_streambuf<wchar_t>* __sbout, bool& __ineof);
855_GLIBCXX_END_NAMESPACE_VERSION
858#include <bits/streambuf.tcc>
860#endif /* _GLIBCXX_STREAMBUF */