1// Input streams -*- C++ -*-
2
3// Copyright (C) 1997-2021 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//
26// ISO C++ 14882: 27.6.1 Input streams
27//
28
29/** @file include/istream
30 * This is a Standard C++ Library header.
31 */
32
33#ifndef _GLIBCXX_ISTREAM
34#define _GLIBCXX_ISTREAM 1
35
36#pragma GCC system_header
37
38#include <ios>
39#include <ostream>
40
41namespace std _GLIBCXX_VISIBILITY(default)
42{
43_GLIBCXX_BEGIN_NAMESPACE_VERSION
44
45 /**
46 * @brief Template class basic_istream.
47 * @ingroup io
48 *
49 * @tparam _CharT Type of character stream.
50 * @tparam _Traits Traits for character type, defaults to
51 * char_traits<_CharT>.
52 *
53 * This is the base class for all input streams. It provides text
54 * formatting of all builtin types, and communicates with any class
55 * derived from basic_streambuf to do the actual input.
56 */
57 template<typename _CharT, typename _Traits>
58 class basic_istream : virtual public basic_ios<_CharT, _Traits>
59 {
60 public:
61 // Types (inherited from basic_ios (27.4.4)):
62 typedef _CharT char_type;
63 typedef typename _Traits::int_type int_type;
64 typedef typename _Traits::pos_type pos_type;
65 typedef typename _Traits::off_type off_type;
66 typedef _Traits traits_type;
67
68 // Non-standard Types:
69 typedef basic_streambuf<_CharT, _Traits> __streambuf_type;
70 typedef basic_ios<_CharT, _Traits> __ios_type;
71 typedef basic_istream<_CharT, _Traits> __istream_type;
72 typedef num_get<_CharT, istreambuf_iterator<_CharT, _Traits> >
73 __num_get_type;
74 typedef ctype<_CharT> __ctype_type;
75
76 protected:
77 // Data Members:
78 /**
79 * The number of characters extracted in the previous unformatted
80 * function; see gcount().
81 */
82 streamsize _M_gcount;
83
84 public:
85 /**
86 * @brief Base constructor.
87 *
88 * This ctor is almost never called by the user directly, rather from
89 * derived classes' initialization lists, which pass a pointer to
90 * their own stream buffer.
91 */
92 explicit
93 basic_istream(__streambuf_type* __sb)
94 : _M_gcount(streamsize(0))
95 { this->init(__sb); }
96
97 /**
98 * @brief Base destructor.
99 *
100 * This does very little apart from providing a virtual base dtor.
101 */
102 virtual
103 ~basic_istream()
104 { _M_gcount = streamsize(0); }
105
106 /// Safe prefix/suffix operations.
107 class sentry;
108 friend class sentry;
109
110 ///@{
111 /**
112 * @brief Interface for manipulators.
113 *
114 * Manipulators such as @c std::ws and @c std::dec use these
115 * functions in constructs like
116 * <code>std::cin >> std::ws</code>.
117 * For more information, see the iomanip header.
118 */
119 __istream_type&
120 operator>>(__istream_type& (*__pf)(__istream_type&))
121 { return __pf(*this); }
122
123 __istream_type&
124 operator>>(__ios_type& (*__pf)(__ios_type&))
125 {
126 __pf(*this);
127 return *this;
128 }
129
130 __istream_type&
131 operator>>(ios_base& (*__pf)(ios_base&))
132 {
133 __pf(*this);
134 return *this;
135 }
136 ///@}
137
138 ///@{
139 /**
140 * @name Extractors
141 *
142 * All the @c operator>> functions (aka <em>formatted input
143 * functions</em>) have some common behavior. Each starts by
144 * constructing a temporary object of type std::basic_istream::sentry
145 * with the second argument (noskipws) set to false. This has several
146 * effects, concluding with the setting of a status flag; see the
147 * sentry documentation for more.
148 *
149 * If the sentry status is good, the function tries to extract
150 * whatever data is appropriate for the type of the argument.
151 *
152 * If an exception is thrown during extraction, ios_base::badbit
153 * will be turned on in the stream's error state (without causing an
154 * ios_base::failure to be thrown) and the original exception will
155 * be rethrown if badbit is set in the exceptions mask.
156 */
157
158 ///@{
159 /**
160 * @brief Integer arithmetic extractors
161 * @param __n A variable of builtin integral type.
162 * @return @c *this if successful
163 *
164 * These functions use the stream's current locale (specifically, the
165 * @c num_get facet) to parse the input data.
166 */
167 __istream_type&
168 operator>>(bool& __n)
169 { return _M_extract(__n); }
170
171 __istream_type&
172 operator>>(short& __n);
173
174 __istream_type&
175 operator>>(unsigned short& __n)
176 { return _M_extract(__n); }
177
178 __istream_type&
179 operator>>(int& __n);
180
181 __istream_type&
182 operator>>(unsigned int& __n)
183 { return _M_extract(__n); }
184
185 __istream_type&
186 operator>>(long& __n)
187 { return _M_extract(__n); }
188
189 __istream_type&
190 operator>>(unsigned long& __n)
191 { return _M_extract(__n); }
192
193#ifdef _GLIBCXX_USE_LONG_LONG
194 __istream_type&
195 operator>>(long long& __n)
196 { return _M_extract(__n); }
197
198 __istream_type&
199 operator>>(unsigned long long& __n)
200 { return _M_extract(__n); }
201#endif
202 ///@}
203
204 ///@{
205 /**
206 * @brief Floating point arithmetic extractors
207 * @param __f A variable of builtin floating point type.
208 * @return @c *this if successful
209 *
210 * These functions use the stream's current locale (specifically, the
211 * @c num_get facet) to parse the input data.
212 */
213 __istream_type&
214 operator>>(float& __f)
215 { return _M_extract(__f); }
216
217 __istream_type&
218 operator>>(double& __f)
219 { return _M_extract(__f); }
220
221 __istream_type&
222 operator>>(long double& __f)
223 { return _M_extract(__f); }
224 ///@}
225
226 /**
227 * @brief Basic arithmetic extractors
228 * @param __p A variable of pointer type.
229 * @return @c *this if successful
230 *
231 * These functions use the stream's current locale (specifically, the
232 * @c num_get facet) to parse the input data.
233 */
234 __istream_type&
235 operator>>(void*& __p)
236 { return _M_extract(__p); }
237
238 /**
239 * @brief Extracting into another streambuf.
240 * @param __sb A pointer to a streambuf
241 *
242 * This function behaves like one of the basic arithmetic extractors,
243 * in that it also constructs a sentry object and has the same error
244 * handling behavior.
245 *
246 * If @p __sb is NULL, the stream will set failbit in its error state.
247 *
248 * Characters are extracted from this stream and inserted into the
249 * @p __sb streambuf until one of the following occurs:
250 *
251 * - the input stream reaches end-of-file,
252 * - insertion into the output buffer fails (in this case, the
253 * character that would have been inserted is not extracted), or
254 * - an exception occurs (and in this case is caught)
255 *
256 * If the function inserts no characters, failbit is set.
257 */
258 __istream_type&
259 operator>>(__streambuf_type* __sb);
260 ///@}
261
262 // [27.6.1.3] unformatted input
263 /**
264 * @brief Character counting
265 * @return The number of characters extracted by the previous
266 * unformatted input function dispatched for this stream.
267 */
268 streamsize
269 gcount() const
270 { return _M_gcount; }
271
272 ///@{
273 /**
274 * @name Unformatted Input Functions
275 *
276 * All the unformatted input functions have some common behavior.
277 * Each starts by constructing a temporary object of type
278 * std::basic_istream::sentry with the second argument (noskipws)
279 * set to true. This has several effects, concluding with the
280 * setting of a status flag; see the sentry documentation for more.
281 *
282 * If the sentry status is good, the function tries to extract
283 * whatever data is appropriate for the type of the argument.
284 *
285 * The number of characters extracted is stored for later retrieval
286 * by gcount().
287 *
288 * If an exception is thrown during extraction, ios_base::badbit
289 * will be turned on in the stream's error state (without causing an
290 * ios_base::failure to be thrown) and the original exception will
291 * be rethrown if badbit is set in the exceptions mask.
292 */
293
294 /**
295 * @brief Simple extraction.
296 * @return A character, or eof().
297 *
298 * Tries to extract a character. If none are available, sets failbit
299 * and returns traits::eof().
300 */
301 int_type
302 get();
303
304 /**
305 * @brief Simple extraction.
306 * @param __c The character in which to store data.
307 * @return *this
308 *
309 * Tries to extract a character and store it in @a __c. If none are
310 * available, sets failbit and returns traits::eof().
311 *
312 * @note This function is not overloaded on signed char and
313 * unsigned char.
314 */
315 __istream_type&
316 get(char_type& __c);
317
318 /**
319 * @brief Simple multiple-character extraction.
320 * @param __s Pointer to an array.
321 * @param __n Maximum number of characters to store in @a __s.
322 * @param __delim A "stop" character.
323 * @return *this
324 *
325 * Characters are extracted and stored into @a __s until one of the
326 * following happens:
327 *
328 * - @c __n-1 characters are stored
329 * - the input sequence reaches EOF
330 * - the next character equals @a __delim, in which case the character
331 * is not extracted
332 *
333 * If no characters are stored, failbit is set in the stream's error
334 * state.
335 *
336 * In any case, a null character is stored into the next location in
337 * the array.
338 *
339 * @note This function is not overloaded on signed char and
340 * unsigned char.
341 */
342 __istream_type&
343 get(char_type* __s, streamsize __n, char_type __delim);
344
345 /**
346 * @brief Simple multiple-character extraction.
347 * @param __s Pointer to an array.
348 * @param __n Maximum number of characters to store in @a s.
349 * @return *this
350 *
351 * Returns @c get(__s,__n,widen(&apos;\\n&apos;)).
352 */
353 __istream_type&
354 get(char_type* __s, streamsize __n)
355 { return this->get(__s, __n, this->widen('\n')); }
356
357 /**
358 * @brief Extraction into another streambuf.
359 * @param __sb A streambuf in which to store data.
360 * @param __delim A "stop" character.
361 * @return *this
362 *
363 * Characters are extracted and inserted into @a __sb until one of the
364 * following happens:
365 *
366 * - the input sequence reaches EOF
367 * - insertion into the output buffer fails (in this case, the
368 * character that would have been inserted is not extracted)
369 * - the next character equals @a __delim (in this case, the character
370 * is not extracted)
371 * - an exception occurs (and in this case is caught)
372 *
373 * If no characters are stored, failbit is set in the stream's error
374 * state.
375 */
376 __istream_type&
377 get(__streambuf_type& __sb, char_type __delim);
378
379 /**
380 * @brief Extraction into another streambuf.
381 * @param __sb A streambuf in which to store data.
382 * @return *this
383 *
384 * Returns @c get(__sb,widen(&apos;\\n&apos;)).
385 */
386 __istream_type&
387 get(__streambuf_type& __sb)
388 { return this->get(__sb, this->widen('\n')); }
389
390 /**
391 * @brief String extraction.
392 * @param __s A character array in which to store the data.
393 * @param __n Maximum number of characters to extract.
394 * @param __delim A "stop" character.
395 * @return *this
396 *
397 * Extracts and stores characters into @a __s until one of the
398 * following happens. Note that these criteria are required to be
399 * tested in the order listed here, to allow an input line to exactly
400 * fill the @a __s array without setting failbit.
401 *
402 * -# the input sequence reaches end-of-file, in which case eofbit
403 * is set in the stream error state
404 * -# the next character equals @c __delim, in which case the character
405 * is extracted (and therefore counted in @c gcount()) but not stored
406 * -# @c __n-1 characters are stored, in which case failbit is set
407 * in the stream error state
408 *
409 * If no characters are extracted, failbit is set. (An empty line of
410 * input should therefore not cause failbit to be set.)
411 *
412 * In any case, a null character is stored in the next location in
413 * the array.
414 */
415 __istream_type&
416 getline(char_type* __s, streamsize __n, char_type __delim);
417
418 /**
419 * @brief String extraction.
420 * @param __s A character array in which to store the data.
421 * @param __n Maximum number of characters to extract.
422 * @return *this
423 *
424 * Returns @c getline(__s,__n,widen(&apos;\\n&apos;)).
425 */
426 __istream_type&
427 getline(char_type* __s, streamsize __n)
428 { return this->getline(__s, __n, this->widen('\n')); }
429
430 /**
431 * @brief Discarding characters
432 * @param __n Number of characters to discard.
433 * @param __delim A "stop" character.
434 * @return *this
435 *
436 * Extracts characters and throws them away until one of the
437 * following happens:
438 * - if @a __n @c != @c std::numeric_limits<int>::max(), @a __n
439 * characters are extracted
440 * - the input sequence reaches end-of-file
441 * - the next character equals @a __delim (in this case, the character
442 * is extracted); note that this condition will never occur if
443 * @a __delim equals @c traits::eof().
444 *
445 * NB: Provide three overloads, instead of the single function
446 * (with defaults) mandated by the Standard: this leads to a
447 * better performing implementation, while still conforming to
448 * the Standard.
449 */
450 __istream_type&
451 ignore(streamsize __n, int_type __delim);
452
453 __istream_type&
454 ignore(streamsize __n);
455
456 __istream_type&
457 ignore();
458
459 /**
460 * @brief Looking ahead in the stream
461 * @return The next character, or eof().
462 *
463 * If, after constructing the sentry object, @c good() is false,
464 * returns @c traits::eof(). Otherwise reads but does not extract
465 * the next input character.
466 */
467 int_type
468 peek();
469
470 /**
471 * @brief Extraction without delimiters.
472 * @param __s A character array.
473 * @param __n Maximum number of characters to store.
474 * @return *this
475 *
476 * If the stream state is @c good(), extracts characters and stores
477 * them into @a __s until one of the following happens:
478 * - @a __n characters are stored
479 * - the input sequence reaches end-of-file, in which case the error
480 * state is set to @c failbit|eofbit.
481 *
482 * @note This function is not overloaded on signed char and
483 * unsigned char.
484 */
485 __istream_type&
486 read(char_type* __s, streamsize __n);
487
488 /**
489 * @brief Extraction until the buffer is exhausted, but no more.
490 * @param __s A character array.
491 * @param __n Maximum number of characters to store.
492 * @return The number of characters extracted.
493 *
494 * Extracts characters and stores them into @a __s depending on the
495 * number of characters remaining in the streambuf's buffer,
496 * @c rdbuf()->in_avail(), called @c A here:
497 * - if @c A @c == @c -1, sets eofbit and extracts no characters
498 * - if @c A @c == @c 0, extracts no characters
499 * - if @c A @c > @c 0, extracts @c min(A,n)
500 *
501 * The goal is to empty the current buffer, and to not request any
502 * more from the external input sequence controlled by the streambuf.
503 */
504 streamsize
505 readsome(char_type* __s, streamsize __n);
506
507 /**
508 * @brief Unextracting a single character.
509 * @param __c The character to push back into the input stream.
510 * @return *this
511 *
512 * If @c rdbuf() is not null, calls @c rdbuf()->sputbackc(c).
513 *
514 * If @c rdbuf() is null or if @c sputbackc() fails, sets badbit in
515 * the error state.
516 *
517 * @note This function first clears eofbit. Since no characters
518 * are extracted, the next call to @c gcount() will return 0,
519 * as required by DR 60.
520 */
521 __istream_type&
522 putback(char_type __c);
523
524 /**
525 * @brief Unextracting the previous character.
526 * @return *this
527 *
528 * If @c rdbuf() is not null, calls @c rdbuf()->sungetc(c).
529 *
530 * If @c rdbuf() is null or if @c sungetc() fails, sets badbit in
531 * the error state.
532 *
533 * @note This function first clears eofbit. Since no characters
534 * are extracted, the next call to @c gcount() will return 0,
535 * as required by DR 60.
536 */
537 __istream_type&
538 unget();
539
540 /**
541 * @brief Synchronizing the stream buffer.
542 * @return 0 on success, -1 on failure
543 *
544 * If @c rdbuf() is a null pointer, returns -1.
545 *
546 * Otherwise, calls @c rdbuf()->pubsync(), and if that returns -1,
547 * sets badbit and returns -1.
548 *
549 * Otherwise, returns 0.
550 *
551 * @note This function does not count the number of characters
552 * extracted, if any, and therefore does not affect the next
553 * call to @c gcount().
554 */
555 int
556 sync();
557
558 /**
559 * @brief Getting the current read position.
560 * @return A file position object.
561 *
562 * If @c fail() is not false, returns @c pos_type(-1) to indicate
563 * failure. Otherwise returns @c rdbuf()->pubseekoff(0,cur,in).
564 *
565 * @note This function does not count the number of characters
566 * extracted, if any, and therefore does not affect the next
567 * call to @c gcount(). At variance with putback, unget and
568 * seekg, eofbit is not cleared first.
569 */
570 pos_type
571 tellg();
572
573 /**
574 * @brief Changing the current read position.
575 * @param __pos A file position object.
576 * @return *this
577 *
578 * If @c fail() is not true, calls @c rdbuf()->pubseekpos(__pos). If
579 * that function fails, sets failbit.
580 *
581 * @note This function first clears eofbit. It does not count the
582 * number of characters extracted, if any, and therefore does
583 * not affect the next call to @c gcount().
584 */
585 __istream_type&
586 seekg(pos_type);
587
588 /**
589 * @brief Changing the current read position.
590 * @param __off A file offset object.
591 * @param __dir The direction in which to seek.
592 * @return *this
593 *
594 * If @c fail() is not true, calls @c rdbuf()->pubseekoff(__off,__dir).
595 * If that function fails, sets failbit.
596 *
597 * @note This function first clears eofbit. It does not count the
598 * number of characters extracted, if any, and therefore does
599 * not affect the next call to @c gcount().
600 */
601 __istream_type&
602 seekg(off_type, ios_base::seekdir);
603 ///@}
604
605 protected:
606 basic_istream()
607 : _M_gcount(streamsize(0))
608 { this->init(0); }
609
610#if __cplusplus >= 201103L
611 basic_istream(const basic_istream&) = delete;
612
613 basic_istream(basic_istream&& __rhs)
614 : __ios_type(), _M_gcount(__rhs._M_gcount)
615 {
616 __ios_type::move(__rhs);
617 __rhs._M_gcount = 0;
618 }
619
620 // 27.7.3.3 Assign/swap
621
622 basic_istream& operator=(const basic_istream&) = delete;
623
624 basic_istream&
625 operator=(basic_istream&& __rhs)
626 {
627 swap(__rhs);
628 return *this;
629 }
630
631 void
632 swap(basic_istream& __rhs)
633 {
634 __ios_type::swap(__rhs);
635 std::swap(_M_gcount, __rhs._M_gcount);
636 }
637#endif
638
639 template<typename _ValueT>
640 __istream_type&
641 _M_extract(_ValueT& __v);
642 };
643
644 /// Explicit specialization declarations, defined in src/istream.cc.
645 template<>
646 basic_istream<char>&
647 basic_istream<char>::
648 getline(char_type* __s, streamsize __n, char_type __delim);
649
650 template<>
651 basic_istream<char>&
652 basic_istream<char>::
653 ignore(streamsize __n);
654
655 template<>
656 basic_istream<char>&
657 basic_istream<char>::
658 ignore(streamsize __n, int_type __delim);
659
660#ifdef _GLIBCXX_USE_WCHAR_T
661 template<>
662 basic_istream<wchar_t>&
663 basic_istream<wchar_t>::
664 getline(char_type* __s, streamsize __n, char_type __delim);
665
666 template<>
667 basic_istream<wchar_t>&
668 basic_istream<wchar_t>::
669 ignore(streamsize __n);
670
671 template<>
672 basic_istream<wchar_t>&
673 basic_istream<wchar_t>::
674 ignore(streamsize __n, int_type __delim);
675#endif
676
677 /**
678 * @brief Performs setup work for input streams.
679 *
680 * Objects of this class are created before all of the standard
681 * extractors are run. It is responsible for <em>exception-safe
682 * prefix and suffix operations,</em> although only prefix actions
683 * are currently required by the standard.
684 */
685 template<typename _CharT, typename _Traits>
686 class basic_istream<_CharT, _Traits>::sentry
687 {
688 // Data Members.
689 bool _M_ok;
690
691 public:
692 /// Easy access to dependent types.
693 typedef _Traits traits_type;
694 typedef basic_streambuf<_CharT, _Traits> __streambuf_type;
695 typedef basic_istream<_CharT, _Traits> __istream_type;
696 typedef typename __istream_type::__ctype_type __ctype_type;
697 typedef typename _Traits::int_type __int_type;
698
699 /**
700 * @brief The constructor performs all the work.
701 * @param __is The input stream to guard.
702 * @param __noskipws Whether to consume whitespace or not.
703 *
704 * If the stream state is good (@a __is.good() is true), then the
705 * following actions are performed, otherwise the sentry state
706 * is false (<em>not okay</em>) and failbit is set in the
707 * stream state.
708 *
709 * The sentry's preparatory actions are:
710 *
711 * -# if the stream is tied to an output stream, @c is.tie()->flush()
712 * is called to synchronize the output sequence
713 * -# if @a __noskipws is false, and @c ios_base::skipws is set in
714 * @c is.flags(), the sentry extracts and discards whitespace
715 * characters from the stream. The currently imbued locale is
716 * used to determine whether each character is whitespace.
717 *
718 * If the stream state is still good, then the sentry state becomes
719 * true (@a okay).
720 */
721 explicit
722 sentry(basic_istream<_CharT, _Traits>& __is, bool __noskipws = false);
723
724 /**
725 * @brief Quick status checking.
726 * @return The sentry state.
727 *
728 * For ease of use, sentries may be converted to booleans. The
729 * return value is that of the sentry state (true == okay).
730 */
731#if __cplusplus >= 201103L
732 explicit
733#endif
734 operator bool() const
735 { return _M_ok; }
736 };
737
738 ///@{
739 /**
740 * @brief Character extractors
741 * @param __in An input stream.
742 * @param __c A character reference.
743 * @return in
744 *
745 * Behaves like one of the formatted arithmetic extractors described in
746 * std::basic_istream. After constructing a sentry object with good
747 * status, this function extracts a character (if one is available) and
748 * stores it in @a __c. Otherwise, sets failbit in the input stream.
749 */
750 template<typename _CharT, typename _Traits>
751 basic_istream<_CharT, _Traits>&
752 operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c);
753
754 template<class _Traits>
755 inline basic_istream<char, _Traits>&
756 operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
757 { return (__in >> reinterpret_cast<char&>(__c)); }
758
759 template<class _Traits>
760 inline basic_istream<char, _Traits>&
761 operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
762 { return (__in >> reinterpret_cast<char&>(__c)); }
763 ///@}
764
765
766 template<typename _CharT, typename _Traits>
767 void
768 __istream_extract(basic_istream<_CharT, _Traits>&, _CharT*, streamsize);
769
770 void __istream_extract(istream&, char*, streamsize);
771
772 ///@{
773 /**
774 * @brief Character string extractors
775 * @param __in An input stream.
776 * @param __s A character array (or a pointer to an array before C++20).
777 * @return __in
778 *
779 * Behaves like one of the formatted arithmetic extractors described in
780 * `std::basic_istream`. After constructing a sentry object with good
781 * status, this function extracts up to `n` characters and stores them
782 * into the array `__s`. `n` is defined as:
783 *
784 * - if `width()` is greater than zero, `n` is `min(width(), n)`
785 * - otherwise `n` is the number of elements of the array
786 * - (before C++20 the pointer is assumed to point to an array of
787 * the largest possible size for an array of `char_type`).
788 *
789 * Characters are extracted and stored until one of the following happens:
790 * - `n - 1` characters are stored
791 * - EOF is reached
792 * - the next character is whitespace according to the current locale
793 *
794 * `width(0)` is then called for the input stream.
795 *
796 * If no characters are extracted, sets failbit.
797 */
798
799#if __cplusplus <= 201703L
800 template<typename _CharT, typename _Traits>
801 __attribute__((__nonnull__(2), __access__(__write_only__, 2)))
802 inline basic_istream<_CharT, _Traits>&
803 operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
804 {
805#ifdef __OPTIMIZE__
806 // Function inlining might make the buffer size known, allowing us to
807 // prevent overflow.
808 size_t __n = __builtin_object_size(__s, 0);
809 if (__n < sizeof(_CharT))
810 {
811 // There is not even space for the required null terminator.
812 __glibcxx_assert(__n >= sizeof(_CharT));
813 // No point calling __istream_extract, but still need to reset width.
814 __in.width(0);
815 __in.setstate(ios_base::failbit);
816 }
817 else if (__n != (size_t)-1)
818 {
819 __n /= sizeof(_CharT);
820 streamsize __w = __in.width();
821 std::__istream_extract(__in, __s, __n);
822 if (__in.good() && (__w <= 0 || __n < __w))
823 {
824 // Stopped extracting early to avoid overflowing the buffer,
825 // but might have stopped anyway (and set eofbit) if at EOF.
826 const typename _Traits::int_type __c = __in.rdbuf()->sgetc();
827 const bool __eof = _Traits::eq_int_type(__c, _Traits::eof());
828 if (__builtin_expect(__eof, true)) // Assume EOF, not overflow.
829 __in.setstate(ios_base::eofbit);
830 }
831 }
832 else
833#endif // __OPTIMIZE
834 {
835 // Buffer size is unknown, have to assume it's huge.
836 streamsize __n = __gnu_cxx::__numeric_traits<streamsize>::__max;
837 __n /= sizeof(_CharT);
838 std::__istream_extract(__in, __s, __n);
839 }
840 return __in;
841 }
842
843 template<class _Traits>
844 __attribute__((__nonnull__(2), __access__(__write_only__, 2)))
845 inline basic_istream<char, _Traits>&
846 operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
847 { return __in >> reinterpret_cast<char*>(__s); }
848
849 template<class _Traits>
850 __attribute__((__nonnull__(2), __access__(__write_only__, 2)))
851 inline basic_istream<char, _Traits>&
852 operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
853 { return __in >> reinterpret_cast<char*>(__s); }
854#else
855 // _GLIBCXX_RESOLVE_LIB_DEFECTS
856 // 2499. operator>>(istream&, char*) makes it hard to avoid buffer overflows
857 template<typename _CharT, typename _Traits, size_t _Num>
858 inline basic_istream<_CharT, _Traits>&
859 operator>>(basic_istream<_CharT, _Traits>& __in, _CharT (&__s)[_Num])
860 {
861 static_assert(_Num <= __gnu_cxx::__numeric_traits<streamsize>::__max);
862 std::__istream_extract(__in, __s, _Num);
863 return __in;
864 }
865
866 template<class _Traits, size_t _Num>
867 inline basic_istream<char, _Traits>&
868 operator>>(basic_istream<char, _Traits>& __in, unsigned char (&__s)[_Num])
869 { return __in >> reinterpret_cast<char(&)[_Num]>(__s); }
870
871 template<class _Traits, size_t _Num>
872 inline basic_istream<char, _Traits>&
873 operator>>(basic_istream<char, _Traits>& __in, signed char (&__s)[_Num])
874 { return __in >> reinterpret_cast<char(&)[_Num]>(__s); }
875#endif
876 ///@}
877
878 /**
879 * @brief Template class basic_iostream
880 * @ingroup io
881 *
882 * @tparam _CharT Type of character stream.
883 * @tparam _Traits Traits for character type, defaults to
884 * char_traits<_CharT>.
885 *
886 * This class multiply inherits from the input and output stream classes
887 * simply to provide a single interface.
888 */
889 template<typename _CharT, typename _Traits>
890 class basic_iostream
891 : public basic_istream<_CharT, _Traits>,
892 public basic_ostream<_CharT, _Traits>
893 {
894 public:
895 // _GLIBCXX_RESOLVE_LIB_DEFECTS
896 // 271. basic_iostream missing typedefs
897 // Types (inherited):
898 typedef _CharT char_type;
899 typedef typename _Traits::int_type int_type;
900 typedef typename _Traits::pos_type pos_type;
901 typedef typename _Traits::off_type off_type;
902 typedef _Traits traits_type;
903
904 // Non-standard Types:
905 typedef basic_istream<_CharT, _Traits> __istream_type;
906 typedef basic_ostream<_CharT, _Traits> __ostream_type;
907
908 /**
909 * @brief Constructor does nothing.
910 *
911 * Both of the parent classes are initialized with the same
912 * streambuf pointer passed to this constructor.
913 */
914 explicit
915 basic_iostream(basic_streambuf<_CharT, _Traits>* __sb)
916 : __istream_type(__sb), __ostream_type(__sb) { }
917
918 /**
919 * @brief Destructor does nothing.
920 */
921 virtual
922 ~basic_iostream() { }
923
924 protected:
925 basic_iostream()
926 : __istream_type(), __ostream_type() { }
927
928#if __cplusplus >= 201103L
929 basic_iostream(const basic_iostream&) = delete;
930
931 basic_iostream(basic_iostream&& __rhs)
932 : __istream_type(std::move(__rhs)), __ostream_type(*this)
933 { }
934
935 // 27.7.3.3 Assign/swap
936
937 basic_iostream& operator=(const basic_iostream&) = delete;
938
939 basic_iostream&
940 operator=(basic_iostream&& __rhs)
941 {
942 swap(__rhs);
943 return *this;
944 }
945
946 void
947 swap(basic_iostream& __rhs)
948 { __istream_type::swap(__rhs); }
949#endif
950 };
951
952 /**
953 * @brief Quick and easy way to eat whitespace
954 *
955 * This manipulator extracts whitespace characters, stopping when the
956 * next character is non-whitespace, or when the input sequence is empty.
957 * If the sequence is empty, @c eofbit is set in the stream, but not
958 * @c failbit.
959 *
960 * The current locale is used to distinguish whitespace characters.
961 *
962 * Example:
963 * @code
964 * MyClass mc;
965 *
966 * std::cin >> std::ws >> mc;
967 * @endcode
968 * will skip leading whitespace before calling operator>> on cin and your
969 * object. Note that the same effect can be achieved by creating a
970 * std::basic_istream::sentry inside your definition of operator>>.
971 */
972 template<typename _CharT, typename _Traits>
973 basic_istream<_CharT, _Traits>&
974 ws(basic_istream<_CharT, _Traits>& __is);
975
976#if __cplusplus >= 201103L
977 // C++11 27.7.2.6 Rvalue stream extraction [istream.rvalue]
978 // _GLIBCXX_RESOLVE_LIB_DEFECTS
979 // 2328. Rvalue stream extraction should use perfect forwarding
980 // 1203. More useful rvalue stream insertion
981
982#if __cpp_lib_concepts
983 template<typename _Is, typename _Tp>
984 requires __derived_from_ios_base<_Is>
985 && requires (_Is& __is, _Tp&& __t) { __is >> std::forward<_Tp>(__t); }
986 using __rvalue_stream_extraction_t = _Is&&;
987#else
988 template<typename _Is, typename _Tp,
989 typename = _Require_derived_from_ios_base<_Is>,
990 typename = decltype(std::declval<_Is&>() >> std::declval<_Tp>())>
991 using __rvalue_stream_extraction_t = _Is&&;
992#endif
993
994 /**
995 * @brief Generic extractor for rvalue stream
996 * @param __is An input stream.
997 * @param __x A reference to the extraction target.
998 * @return __is
999 *
1000 * This is just a forwarding function to allow extraction from
1001 * rvalue streams since they won't bind to the extractor functions
1002 * that take an lvalue reference.
1003 */
1004 template<typename _Istream, typename _Tp>
1005 inline __rvalue_stream_extraction_t<_Istream, _Tp>
1006 operator>>(_Istream&& __is, _Tp&& __x)
1007 {
1008 __is >> std::forward<_Tp>(__x);
1009 return std::move(__is);
1010 }
1011#endif // C++11
1012
1013_GLIBCXX_END_NAMESPACE_VERSION
1014} // namespace
1015
1016#include <bits/istream.tcc>
1017
1018#endif /* _GLIBCXX_ISTREAM */
1019

source code of include/c++/11/istream