Line data Source code
1 : // Stream buffer classes -*- C++ -*-
2 :
3 : // Copyright (C) 1997-2019 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 include/streambuf
26 : * This is a Standard C++ Library header.
27 : */
28 :
29 : //
30 : // ISO C++ 14882: 27.5 Stream buffers
31 : //
32 :
33 : #ifndef _GLIBXX_STREAMBUF
34 : #define _GLIBXX_STREAMBUF 1
35 :
36 : #pragma GCC system_header
37 :
38 : #include <bits/c++config.h>
39 : #include <iosfwd>
40 : #include <bits/localefwd.h>
41 : #include <bits/ios_base.h>
42 : #include <bits/cpp_type_traits.h>
43 : #include <ext/type_traits.h>
44 :
45 : namespace std _GLIBCXX_VISIBILITY(default)
46 : {
47 : _GLIBCXX_BEGIN_NAMESPACE_VERSION
48 :
49 : #define _IsUnused __attribute__ ((__unused__))
50 :
51 : template<typename _CharT, typename _Traits>
52 : streamsize
53 : __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
54 : basic_streambuf<_CharT, _Traits>*, bool&);
55 :
56 : /**
57 : * @brief The actual work of input and output (interface).
58 : * @ingroup io
59 : *
60 : * @tparam _CharT Type of character stream.
61 : * @tparam _Traits Traits for character type, defaults to
62 : * char_traits<_CharT>.
63 : *
64 : * This is a base class. Derived stream buffers each control a
65 : * pair of character sequences: one for input, and one for output.
66 : *
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.
70 : *
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
77 : * files.
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.
84 : * .
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).
99 : * .
100 : * -# The following semantic constraints shall always apply for any set
101 : * of three pointers for a sequence, using the pointer names given
102 : * immediately above:
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).
120 : */
121 : template<typename _CharT, typename _Traits>
122 : class basic_streambuf
123 : {
124 : public:
125 : ///@{
126 : /**
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.
130 : */
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;
136 : ///@}
137 :
138 : ///@{
139 : /// This is a non-standard type.
140 : typedef basic_streambuf<char_type, traits_type> __streambuf_type;
141 : ///@}
142 :
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>;
148 :
149 : friend streamsize
150 : __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&);
151 :
152 : template<bool _IsMove, typename _CharT2>
153 : friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
154 : _CharT2*>::__type
155 : __copy_move_a2(istreambuf_iterator<_CharT2>,
156 : istreambuf_iterator<_CharT2>, _CharT2*);
157 :
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>,
162 : const _CharT2&);
163 :
164 : template<typename _CharT2, typename _Distance>
165 : friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
166 : void>::__type
167 : advance(istreambuf_iterator<_CharT2>&, _Distance);
168 :
169 : template<typename _CharT2, typename _Traits2>
170 : friend basic_istream<_CharT2, _Traits2>&
171 : operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
172 :
173 : template<typename _CharT2, typename _Traits2, typename _Alloc>
174 : friend basic_istream<_CharT2, _Traits2>&
175 : operator>>(basic_istream<_CharT2, _Traits2>&,
176 : basic_string<_CharT2, _Traits2, _Alloc>&);
177 :
178 : template<typename _CharT2, typename _Traits2, typename _Alloc>
179 : friend basic_istream<_CharT2, _Traits2>&
180 : getline(basic_istream<_CharT2, _Traits2>&,
181 : basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
182 :
183 : protected:
184 : /*
185 : * This is based on _IO_FILE, just reordered to be more consistent,
186 : * and is intended to be the most minimal abstraction for an
187 : * internal buffer.
188 : * - get == input == read
189 : * - put == output == write
190 : */
191 : char_type* _M_in_beg; ///< Start of get area.
192 : char_type* _M_in_cur; ///< Current read area.
193 : char_type* _M_in_end; ///< End of get area.
194 : char_type* _M_out_beg; ///< Start of put area.
195 : char_type* _M_out_cur; ///< Current put area.
196 : char_type* _M_out_end; ///< End of put area.
197 :
198 : /// Current locale setting.
199 : locale _M_buf_locale;
200 :
201 : public:
202 : /// Destructor deallocates no buffer space.
203 : virtual
204 28851 : ~basic_streambuf()
205 28851 : { }
206 :
207 : // [27.5.2.2.1] locales
208 : /**
209 : * @brief Entry point for imbue().
210 : * @param __loc The new locale.
211 : * @return The previous locale.
212 : *
213 : * Calls the derived imbue(__loc).
214 : */
215 : locale
216 : pubimbue(const locale& __loc)
217 : {
218 : locale __tmp(this->getloc());
219 : this->imbue(__loc);
220 : _M_buf_locale = __loc;
221 : return __tmp;
222 : }
223 :
224 : /**
225 : * @brief Locale access.
226 : * @return The current locale in effect.
227 : *
228 : * If pubimbue(loc) has been called, then the most recent @c loc
229 : * is returned. Otherwise the global locale in effect at the time
230 : * of construction is returned.
231 : */
232 : locale
233 : getloc() const
234 : { return _M_buf_locale; }
235 :
236 : // [27.5.2.2.2] buffer management and positioning
237 : ///@{
238 : /**
239 : * @brief Entry points for derived buffer functions.
240 : *
241 : * The public versions of @c pubfoo dispatch to the protected
242 : * derived @c foo member functions, passing the arguments (if any)
243 : * and returning the result unchanged.
244 : */
245 : basic_streambuf*
246 : pubsetbuf(char_type* __s, streamsize __n)
247 : { return this->setbuf(__s, __n); }
248 :
249 : /**
250 : * @brief Alters the stream position.
251 : * @param __off Offset.
252 : * @param __way Value for ios_base::seekdir.
253 : * @param __mode Value for ios_base::openmode.
254 : *
255 : * Calls virtual seekoff function.
256 : */
257 : pos_type
258 : pubseekoff(off_type __off, ios_base::seekdir __way,
259 : ios_base::openmode __mode = ios_base::in | ios_base::out)
260 : { return this->seekoff(__off, __way, __mode); }
261 :
262 : /**
263 : * @brief Alters the stream position.
264 : * @param __sp Position
265 : * @param __mode Value for ios_base::openmode.
266 : *
267 : * Calls virtual seekpos function.
268 : */
269 : pos_type
270 : pubseekpos(pos_type __sp,
271 : ios_base::openmode __mode = ios_base::in | ios_base::out)
272 : { return this->seekpos(__sp, __mode); }
273 :
274 : /**
275 : * @brief Calls virtual sync function.
276 : */
277 : int
278 0 : pubsync() { return this->sync(); }
279 : ///@}
280 :
281 : // [27.5.2.2.3] get area
282 : /**
283 : * @brief Looking ahead into the stream.
284 : * @return The number of characters available.
285 : *
286 : * If a read position is available, returns the number of characters
287 : * available for reading before the buffer must be refilled.
288 : * Otherwise returns the derived @c showmanyc().
289 : */
290 : streamsize
291 : in_avail()
292 : {
293 : const streamsize __ret = this->egptr() - this->gptr();
294 : return __ret ? __ret : this->showmanyc();
295 : }
296 :
297 : /**
298 : * @brief Getting the next character.
299 : * @return The next character, or eof.
300 : *
301 : * Calls @c sbumpc(), and if that function returns
302 : * @c traits::eof(), so does this function. Otherwise, @c sgetc().
303 : */
304 : int_type
305 : snextc()
306 : {
307 : int_type __ret = traits_type::eof();
308 : if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(),
309 : __ret), true))
310 : __ret = this->sgetc();
311 : return __ret;
312 : }
313 :
314 : /**
315 : * @brief Getting the next character.
316 : * @return The next character, or eof.
317 : *
318 : * If the input read position is available, returns that character
319 : * and increments the read pointer, otherwise calls and returns
320 : * @c uflow().
321 : */
322 : int_type
323 0 : sbumpc()
324 : {
325 : int_type __ret;
326 0 : if (__builtin_expect(this->gptr() < this->egptr(), true))
327 : {
328 0 : __ret = traits_type::to_int_type(*this->gptr());
329 0 : this->gbump(1);
330 : }
331 : else
332 0 : __ret = this->uflow();
333 : return __ret;
334 : }
335 :
336 : /**
337 : * @brief Getting the next character.
338 : * @return The next character, or eof.
339 : *
340 : * If the input read position is available, returns that character,
341 : * otherwise calls and returns @c underflow(). Does not move the
342 : * read position after fetching the character.
343 : */
344 : int_type
345 : sgetc()
346 : {
347 : int_type __ret;
348 : if (__builtin_expect(this->gptr() < this->egptr(), true))
349 : __ret = traits_type::to_int_type(*this->gptr());
350 : else
351 : __ret = this->underflow();
352 : return __ret;
353 : }
354 :
355 : /**
356 : * @brief Entry point for xsgetn.
357 : * @param __s A buffer area.
358 : * @param __n A count.
359 : *
360 : * Returns xsgetn(__s,__n). The effect is to fill @a __s[0] through
361 : * @a __s[__n-1] with characters from the input sequence, if possible.
362 : */
363 : streamsize
364 : sgetn(char_type* __s, streamsize __n)
365 : { return this->xsgetn(__s, __n); }
366 :
367 : // [27.5.2.2.4] putback
368 : /**
369 : * @brief Pushing characters back into the input stream.
370 : * @param __c The character to push back.
371 : * @return The previous character, if possible.
372 : *
373 : * Similar to sungetc(), but @a __c is pushed onto the stream
374 : * instead of <em>the previous character.</em> If successful,
375 : * the next character fetched from the input stream will be @a
376 : * __c.
377 : */
378 : int_type
379 : sputbackc(char_type __c)
380 : {
381 : int_type __ret;
382 : const bool __testpos = this->eback() < this->gptr();
383 : if (__builtin_expect(!__testpos ||
384 : !traits_type::eq(__c, this->gptr()[-1]), false))
385 : __ret = this->pbackfail(traits_type::to_int_type(__c));
386 : else
387 : {
388 : this->gbump(-1);
389 : __ret = traits_type::to_int_type(*this->gptr());
390 : }
391 : return __ret;
392 : }
393 :
394 : /**
395 : * @brief Moving backwards in the input stream.
396 : * @return The previous character, if possible.
397 : *
398 : * If a putback position is available, this function decrements
399 : * the input pointer and returns that character. Otherwise,
400 : * calls and returns pbackfail(). The effect is to @a unget
401 : * the last character @a gotten.
402 : */
403 : int_type
404 : sungetc()
405 : {
406 : int_type __ret;
407 : if (__builtin_expect(this->eback() < this->gptr(), true))
408 : {
409 : this->gbump(-1);
410 : __ret = traits_type::to_int_type(*this->gptr());
411 : }
412 : else
413 : __ret = this->pbackfail();
414 : return __ret;
415 : }
416 :
417 : // [27.5.2.2.5] put area
418 : /**
419 : * @brief Entry point for all single-character output functions.
420 : * @param __c A character to output.
421 : * @return @a __c, if possible.
422 : *
423 : * One of two public output functions.
424 : *
425 : * If a write position is available for the output sequence (i.e.,
426 : * the buffer is not full), stores @a __c in that position, increments
427 : * the position, and returns @c traits::to_int_type(__c). If a write
428 : * position is not available, returns @c overflow(__c).
429 : */
430 : int_type
431 0 : sputc(char_type __c)
432 : {
433 : int_type __ret;
434 0 : if (__builtin_expect(this->pptr() < this->epptr(), true))
435 : {
436 0 : *this->pptr() = __c;
437 0 : this->pbump(1);
438 0 : __ret = traits_type::to_int_type(__c);
439 : }
440 : else
441 0 : __ret = this->overflow(traits_type::to_int_type(__c));
442 : return __ret;
443 : }
444 :
445 : /**
446 : * @brief Entry point for all single-character output functions.
447 : * @param __s A buffer read area.
448 : * @param __n A count.
449 : *
450 : * One of two public output functions.
451 : *
452 : *
453 : * Returns xsputn(__s,__n). The effect is to write @a __s[0] through
454 : * @a __s[__n-1] to the output sequence, if possible.
455 : */
456 : streamsize
457 0 : sputn(const char_type* __s, streamsize __n)
458 0 : { return this->xsputn(__s, __n); }
459 :
460 : protected:
461 : /**
462 : * @brief Base constructor.
463 : *
464 : * Only called from derived constructors, and sets up all the
465 : * buffer data to zero, including the pointers described in the
466 : * basic_streambuf class description. Note that, as a result,
467 : * - the class starts with no read nor write positions available,
468 : * - this is not an error
469 : */
470 28852 : basic_streambuf()
471 : : _M_in_beg(0), _M_in_cur(0), _M_in_end(0),
472 : _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
473 28852 : _M_buf_locale(locale())
474 : { }
475 :
476 : // [27.5.2.3.1] get area access
477 : ///@{
478 : /**
479 : * @brief Access to the get area.
480 : *
481 : * These functions are only available to other protected functions,
482 : * including derived classes.
483 : *
484 : * - eback() returns the beginning pointer for the input sequence
485 : * - gptr() returns the next pointer for the input sequence
486 : * - egptr() returns the end pointer for the input sequence
487 : */
488 : char_type*
489 0 : eback() const { return _M_in_beg; }
490 :
491 : char_type*
492 0 : gptr() const { return _M_in_cur; }
493 :
494 : char_type*
495 0 : egptr() const { return _M_in_end; }
496 : ///@}
497 :
498 : /**
499 : * @brief Moving the read position.
500 : * @param __n The delta by which to move.
501 : *
502 : * This just advances the read position without returning any data.
503 : */
504 : void
505 0 : gbump(int __n) { _M_in_cur += __n; }
506 :
507 : /**
508 : * @brief Setting the three read area pointers.
509 : * @param __gbeg A pointer.
510 : * @param __gnext A pointer.
511 : * @param __gend A pointer.
512 : * @post @a __gbeg == @c eback(), @a __gnext == @c gptr(), and
513 : * @a __gend == @c egptr()
514 : */
515 : void
516 0 : setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
517 : {
518 0 : _M_in_beg = __gbeg;
519 0 : _M_in_cur = __gnext;
520 0 : _M_in_end = __gend;
521 0 : }
522 :
523 : // [27.5.2.3.2] put area access
524 : ///@{
525 : /**
526 : * @brief Access to the put area.
527 : *
528 : * These functions are only available to other protected functions,
529 : * including derived classes.
530 : *
531 : * - pbase() returns the beginning pointer for the output sequence
532 : * - pptr() returns the next pointer for the output sequence
533 : * - epptr() returns the end pointer for the output sequence
534 : */
535 : char_type*
536 0 : pbase() const { return _M_out_beg; }
537 :
538 : char_type*
539 0 : pptr() const { return _M_out_cur; }
540 :
541 : char_type*
542 0 : epptr() const { return _M_out_end; }
543 : ///@}
544 :
545 : /**
546 : * @brief Moving the write position.
547 : * @param __n The delta by which to move.
548 : *
549 : * This just advances the write position without returning any data.
550 : */
551 : void
552 0 : pbump(int __n) { _M_out_cur += __n; }
553 :
554 : /**
555 : * @brief Setting the three write area pointers.
556 : * @param __pbeg A pointer.
557 : * @param __pend A pointer.
558 : * @post @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and
559 : * @a __pend == @c epptr()
560 : */
561 : void
562 0 : setp(char_type* __pbeg, char_type* __pend)
563 : {
564 0 : _M_out_beg = _M_out_cur = __pbeg;
565 0 : _M_out_end = __pend;
566 : }
567 :
568 : // [27.5.2.4] virtual functions
569 : // [27.5.2.4.1] locales
570 : /**
571 : * @brief Changes translations.
572 : * @param __loc A new locale.
573 : *
574 : * Translations done during I/O which depend on the current
575 : * locale are changed by this call. The standard adds,
576 : * <em>Between invocations of this function a class derived
577 : * from streambuf can safely cache results of calls to locale
578 : * functions and to members of facets so obtained.</em>
579 : *
580 : * @note Base class version does nothing.
581 : */
582 : virtual void
583 : imbue(const locale& __loc _IsUnused)
584 : { }
585 :
586 : // [27.5.2.4.2] buffer management and positioning
587 : /**
588 : * @brief Manipulates the buffer.
589 : *
590 : * Each derived class provides its own appropriate behavior. See
591 : * the next-to-last paragraph of
592 : * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
593 : * for more on this function.
594 : *
595 : * @note Base class version does nothing, returns @c this.
596 : */
597 : virtual basic_streambuf<char_type,_Traits>*
598 : setbuf(char_type*, streamsize)
599 : { return this; }
600 :
601 : /**
602 : * @brief Alters the stream positions.
603 : *
604 : * Each derived class provides its own appropriate behavior.
605 : * @note Base class version does nothing, returns a @c pos_type
606 : * that represents an invalid stream position.
607 : */
608 : virtual pos_type
609 : seekoff(off_type, ios_base::seekdir,
610 : ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
611 : { return pos_type(off_type(-1)); }
612 :
613 : /**
614 : * @brief Alters the stream positions.
615 : *
616 : * Each derived class provides its own appropriate behavior.
617 : * @note Base class version does nothing, returns a @c pos_type
618 : * that represents an invalid stream position.
619 : */
620 : virtual pos_type
621 : seekpos(pos_type,
622 : ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
623 : { return pos_type(off_type(-1)); }
624 :
625 : /**
626 : * @brief Synchronizes the buffer arrays with the controlled sequences.
627 : * @return -1 on failure.
628 : *
629 : * Each derived class provides its own appropriate behavior,
630 : * including the definition of @a failure.
631 : * @note Base class version does nothing, returns zero.
632 : */
633 : virtual int
634 : sync() { return 0; }
635 :
636 : // [27.5.2.4.3] get area
637 : /**
638 : * @brief Investigating the data available.
639 : * @return An estimate of the number of characters available in the
640 : * input sequence, or -1.
641 : *
642 : * <em>If it returns a positive value, then successive calls to
643 : * @c underflow() will not return @c traits::eof() until at
644 : * least that number of characters have been supplied. If @c
645 : * showmanyc() returns -1, then calls to @c underflow() or @c
646 : * uflow() will fail.</em> [27.5.2.4.3]/1
647 : *
648 : * @note Base class version does nothing, returns zero.
649 : * @note The standard adds that <em>the intention is not only that the
650 : * calls [to underflow or uflow] will not return @c eof() but
651 : * that they will return immediately.</em>
652 : * @note The standard adds that <em>the morphemes of @c showmanyc are
653 : * @b es-how-many-see, not @b show-manic.</em>
654 : */
655 : virtual streamsize
656 : showmanyc() { return 0; }
657 :
658 : /**
659 : * @brief Multiple character extraction.
660 : * @param __s A buffer area.
661 : * @param __n Maximum number of characters to assign.
662 : * @return The number of characters assigned.
663 : *
664 : * Fills @a __s[0] through @a __s[__n-1] with characters from the input
665 : * sequence, as if by @c sbumpc(). Stops when either @a __n characters
666 : * have been copied, or when @c traits::eof() would be copied.
667 : *
668 : * It is expected that derived classes provide a more efficient
669 : * implementation by overriding this definition.
670 : */
671 : virtual streamsize
672 : xsgetn(char_type* __s, streamsize __n);
673 :
674 : /**
675 : * @brief Fetches more data from the controlled sequence.
676 : * @return The first character from the <em>pending sequence</em>.
677 : *
678 : * Informally, this function is called when the input buffer is
679 : * exhausted (or does not exist, as buffering need not actually be
680 : * done). If a buffer exists, it is @a refilled. In either case, the
681 : * next available character is returned, or @c traits::eof() to
682 : * indicate a null pending sequence.
683 : *
684 : * For a formal definition of the pending sequence, see a good text
685 : * such as Langer & Kreft, or [27.5.2.4.3]/7-14.
686 : *
687 : * A functioning input streambuf can be created by overriding only
688 : * this function (no buffer area will be used). For an example, see
689 : * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html
690 : *
691 : * @note Base class version does nothing, returns eof().
692 : */
693 : virtual int_type
694 : underflow()
695 : { return traits_type::eof(); }
696 :
697 : /**
698 : * @brief Fetches more data from the controlled sequence.
699 : * @return The first character from the <em>pending sequence</em>.
700 : *
701 : * Informally, this function does the same thing as @c underflow(),
702 : * and in fact is required to call that function. It also returns
703 : * the new character, like @c underflow() does. However, this
704 : * function also moves the read position forward by one.
705 : */
706 : virtual int_type
707 : uflow()
708 : {
709 : int_type __ret = traits_type::eof();
710 : const bool __testeof = traits_type::eq_int_type(this->underflow(),
711 : __ret);
712 : if (!__testeof)
713 : {
714 : __ret = traits_type::to_int_type(*this->gptr());
715 : this->gbump(1);
716 : }
717 : return __ret;
718 : }
719 :
720 : // [27.5.2.4.4] putback
721 : /**
722 : * @brief Tries to back up the input sequence.
723 : * @param __c The character to be inserted back into the sequence.
724 : * @return eof() on failure, <em>some other value</em> on success
725 : * @post The constraints of @c gptr(), @c eback(), and @c pptr()
726 : * are the same as for @c underflow().
727 : *
728 : * @note Base class version does nothing, returns eof().
729 : */
730 : virtual int_type
731 : pbackfail(int_type __c _IsUnused = traits_type::eof())
732 : { return traits_type::eof(); }
733 :
734 : // Put area:
735 : /**
736 : * @brief Multiple character insertion.
737 : * @param __s A buffer area.
738 : * @param __n Maximum number of characters to write.
739 : * @return The number of characters written.
740 : *
741 : * Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if
742 : * by @c sputc(). Stops when either @a n characters have been
743 : * copied, or when @c sputc() would return @c traits::eof().
744 : *
745 : * It is expected that derived classes provide a more efficient
746 : * implementation by overriding this definition.
747 : */
748 : virtual streamsize
749 : xsputn(const char_type* __s, streamsize __n);
750 :
751 : /**
752 : * @brief Consumes data from the buffer; writes to the
753 : * controlled sequence.
754 : * @param __c An additional character to consume.
755 : * @return eof() to indicate failure, something else (usually
756 : * @a __c, or not_eof())
757 : *
758 : * Informally, this function is called when the output buffer
759 : * is full (or does not exist, as buffering need not actually
760 : * be done). If a buffer exists, it is @a consumed, with
761 : * <em>some effect</em> on the controlled sequence.
762 : * (Typically, the buffer is written out to the sequence
763 : * verbatim.) In either case, the character @a c is also
764 : * written out, if @a __c is not @c eof().
765 : *
766 : * For a formal definition of this function, see a good text
767 : * such as Langer & Kreft, or [27.5.2.4.5]/3-7.
768 : *
769 : * A functioning output streambuf can be created by overriding only
770 : * this function (no buffer area will be used).
771 : *
772 : * @note Base class version does nothing, returns eof().
773 : */
774 : virtual int_type
775 : overflow(int_type __c _IsUnused = traits_type::eof())
776 : { return traits_type::eof(); }
777 :
778 : #if _GLIBCXX_USE_DEPRECATED && __cplusplus <= 201402L
779 : // Annex D.6 (removed in C++17)
780 : public:
781 : /**
782 : * @brief Tosses a character.
783 : *
784 : * Advances the read pointer, ignoring the character that would have
785 : * been read.
786 : *
787 : * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
788 : */
789 : _GLIBCXX_DEPRECATED_SUGGEST("std::basic_streambuf::sbumpc")
790 : void
791 : stossc()
792 : {
793 : if (this->gptr() < this->egptr())
794 : this->gbump(1);
795 : else
796 : this->uflow();
797 : }
798 : #endif
799 :
800 : // Also used by specializations for char and wchar_t in src.
801 : void
802 : __safe_gbump(streamsize __n) { _M_in_cur += __n; }
803 :
804 : void
805 : __safe_pbump(streamsize __n) { _M_out_cur += __n; }
806 :
807 : #if __cplusplus < 201103L
808 : private:
809 : #else
810 : protected:
811 : #endif
812 : basic_streambuf(const basic_streambuf&);
813 :
814 : basic_streambuf&
815 : operator=(const basic_streambuf&);
816 :
817 : #if __cplusplus >= 201103L
818 : void
819 : swap(basic_streambuf& __sb)
820 : {
821 : std::swap(_M_in_beg, __sb._M_in_beg);
822 : std::swap(_M_in_cur, __sb._M_in_cur);
823 : std::swap(_M_in_end, __sb._M_in_end);
824 : std::swap(_M_out_beg, __sb._M_out_beg);
825 : std::swap(_M_out_cur, __sb._M_out_cur);
826 : std::swap(_M_out_end, __sb._M_out_end);
827 : std::swap(_M_buf_locale, __sb._M_buf_locale);
828 : }
829 : #endif
830 : };
831 :
832 : #if __cplusplus >= 201103L
833 : template<typename _CharT, typename _Traits>
834 : std::basic_streambuf<_CharT, _Traits>::
835 : basic_streambuf(const basic_streambuf&) = default;
836 :
837 : template<typename _CharT, typename _Traits>
838 : std::basic_streambuf<_CharT, _Traits>&
839 : std::basic_streambuf<_CharT, _Traits>::
840 : operator=(const basic_streambuf&) = default;
841 : #endif
842 :
843 : // Explicit specialization declarations, defined in src/streambuf.cc.
844 : template<>
845 : streamsize
846 : __copy_streambufs_eof(basic_streambuf<char>* __sbin,
847 : basic_streambuf<char>* __sbout, bool& __ineof);
848 : #ifdef _GLIBCXX_USE_WCHAR_T
849 : template<>
850 : streamsize
851 : __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
852 : basic_streambuf<wchar_t>* __sbout, bool& __ineof);
853 : #endif
854 :
855 : #undef _IsUnused
856 :
857 : _GLIBCXX_END_NAMESPACE_VERSION
858 : } // namespace
859 :
860 : #include <bits/streambuf.tcc>
861 :
862 : #endif /* _GLIBCXX_STREAMBUF */
|
