1// Output 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/** @file include/ostream
26 * This is a Standard C++ Library header.
27 */
28
29//
30// ISO C++ 14882: 27.6.2 Output streams
31//
32
33#ifndef _GLIBCXX_OSTREAM
34#define _GLIBCXX_OSTREAM 1
35
36#pragma GCC system_header
37
38#include <ios>
39#include <bits/ostream_insert.h>
40
41namespace std _GLIBCXX_VISIBILITY(default)
42{
43_GLIBCXX_BEGIN_NAMESPACE_VERSION
44
45 /**
46 * @brief Template class basic_ostream.
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 output streams. It provides text
54 * formatting of all builtin types, and communicates with any class
55 * derived from basic_streambuf to do the actual output.
56 */
57 template<typename _CharT, typename _Traits>
58 class basic_ostream : virtual public basic_ios<_CharT, _Traits>
59 {
60 public:
61 // Types (inherited from basic_ios):
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_ostream<_CharT, _Traits> __ostream_type;
72 typedef num_put<_CharT, ostreambuf_iterator<_CharT, _Traits> >
73 __num_put_type;
74 typedef ctype<_CharT> __ctype_type;
75
76 /**
77 * @brief Base constructor.
78 *
79 * This ctor is almost never called by the user directly, rather from
80 * derived classes' initialization lists, which pass a pointer to
81 * their own stream buffer.
82 */
83 explicit
84 basic_ostream(__streambuf_type* __sb)
85 { this->init(__sb); }
86
87 /**
88 * @brief Base destructor.
89 *
90 * This does very little apart from providing a virtual base dtor.
91 */
92 virtual
93 ~basic_ostream() { }
94
95 /// Safe prefix/suffix operations.
96 class sentry;
97 friend class sentry;
98
99 ///@{
100 /**
101 * @brief Interface for manipulators.
102 *
103 * Manipulators such as @c std::endl and @c std::hex use these
104 * functions in constructs like "std::cout << std::endl". For more
105 * information, see the iomanip header.
106 */
107 __ostream_type&
108 operator<<(__ostream_type& (*__pf)(__ostream_type&))
109 {
110 // _GLIBCXX_RESOLVE_LIB_DEFECTS
111 // DR 60. What is a formatted input function?
112 // The inserters for manipulators are *not* formatted output functions.
113 return __pf(*this);
114 }
115
116 __ostream_type&
117 operator<<(__ios_type& (*__pf)(__ios_type&))
118 {
119 // _GLIBCXX_RESOLVE_LIB_DEFECTS
120 // DR 60. What is a formatted input function?
121 // The inserters for manipulators are *not* formatted output functions.
122 __pf(*this);
123 return *this;
124 }
125
126 __ostream_type&
127 operator<<(ios_base& (*__pf) (ios_base&))
128 {
129 // _GLIBCXX_RESOLVE_LIB_DEFECTS
130 // DR 60. What is a formatted input function?
131 // The inserters for manipulators are *not* formatted output functions.
132 __pf(*this);
133 return *this;
134 }
135 ///@}
136
137 ///@{
138 /**
139 * @name Inserters
140 *
141 * All the @c operator<< functions (aka <em>formatted output
142 * functions</em>) have some common behavior. Each starts by
143 * constructing a temporary object of type std::basic_ostream::sentry.
144 * This can have several effects, concluding with the setting of a
145 * status flag; see the sentry documentation for more.
146 *
147 * If the sentry status is good, the function tries to generate
148 * whatever data is appropriate for the type of the argument.
149 *
150 * If an exception is thrown during insertion, ios_base::badbit
151 * will be turned on in the stream's error state without causing an
152 * ios_base::failure to be thrown. The original exception will then
153 * be rethrown.
154 */
155
156 ///@{
157 /**
158 * @brief Integer arithmetic inserters
159 * @param __n A variable of builtin integral type.
160 * @return @c *this if successful
161 *
162 * These functions use the stream's current locale (specifically, the
163 * @c num_get facet) to perform numeric formatting.
164 */
165 __ostream_type&
166 operator<<(long __n)
167 { return _M_insert(__n); }
168
169 __ostream_type&
170 operator<<(unsigned long __n)
171 { return _M_insert(__n); }
172
173 __ostream_type&
174 operator<<(bool __n)
175 { return _M_insert(__n); }
176
177 __ostream_type&
178 operator<<(short __n);
179
180 __ostream_type&
181 operator<<(unsigned short __n)
182 {
183 // _GLIBCXX_RESOLVE_LIB_DEFECTS
184 // 117. basic_ostream uses nonexistent num_put member functions.
185 return _M_insert(static_cast<unsigned long>(__n));
186 }
187
188 __ostream_type&
189 operator<<(int __n);
190
191 __ostream_type&
192 operator<<(unsigned int __n)
193 {
194 // _GLIBCXX_RESOLVE_LIB_DEFECTS
195 // 117. basic_ostream uses nonexistent num_put member functions.
196 return _M_insert(static_cast<unsigned long>(__n));
197 }
198
199#ifdef _GLIBCXX_USE_LONG_LONG
200 __ostream_type&
201 operator<<(long long __n)
202 { return _M_insert(__n); }
203
204 __ostream_type&
205 operator<<(unsigned long long __n)
206 { return _M_insert(__n); }
207#endif
208 ///@}
209
210 ///@{
211 /**
212 * @brief Floating point arithmetic inserters
213 * @param __f A variable of builtin floating point type.
214 * @return @c *this if successful
215 *
216 * These functions use the stream's current locale (specifically, the
217 * @c num_get facet) to perform numeric formatting.
218 */
219 __ostream_type&
220 operator<<(double __f)
221 { return _M_insert(__f); }
222
223 __ostream_type&
224 operator<<(float __f)
225 {
226 // _GLIBCXX_RESOLVE_LIB_DEFECTS
227 // 117. basic_ostream uses nonexistent num_put member functions.
228 return _M_insert(static_cast<double>(__f));
229 }
230
231 __ostream_type&
232 operator<<(long double __f)
233 { return _M_insert(__f); }
234 ///@}
235
236 /**
237 * @brief Pointer arithmetic inserters
238 * @param __p A variable of pointer type.
239 * @return @c *this if successful
240 *
241 * These functions use the stream's current locale (specifically, the
242 * @c num_get facet) to perform numeric formatting.
243 */
244 __ostream_type&
245 operator<<(const void* __p)
246 { return _M_insert(__p); }
247
248#if __cplusplus >= 201703L
249 __ostream_type&
250 operator<<(nullptr_t)
251 { return *this << "nullptr"; }
252#endif
253
254#if __cplusplus > 202002L
255 __attribute__((__always_inline__))
256 __ostream_type&
257 operator<<(const volatile void* __p)
258 { return _M_insert(const_cast<const void*>(__p)); }
259#endif
260
261 /**
262 * @brief Extracting from another streambuf.
263 * @param __sb A pointer to a streambuf
264 *
265 * This function behaves like one of the basic arithmetic extractors,
266 * in that it also constructs a sentry object and has the same error
267 * handling behavior.
268 *
269 * If @p __sb is NULL, the stream will set failbit in its error state.
270 *
271 * Characters are extracted from @p __sb and inserted into @c *this
272 * until one of the following occurs:
273 *
274 * - the input stream reaches end-of-file,
275 * - insertion into the output sequence fails (in this case, the
276 * character that would have been inserted is not extracted), or
277 * - an exception occurs while getting a character from @p __sb, which
278 * sets failbit in the error state
279 *
280 * If the function inserts no characters, failbit is set.
281 */
282 __ostream_type&
283 operator<<(__streambuf_type* __sb);
284 ///@}
285
286 ///@{
287 /**
288 * @name Unformatted Output Functions
289 *
290 * All the unformatted output functions have some common behavior.
291 * Each starts by constructing a temporary object of type
292 * std::basic_ostream::sentry. This has several effects, concluding
293 * with the setting of a status flag; see the sentry documentation
294 * for more.
295 *
296 * If the sentry status is good, the function tries to generate
297 * whatever data is appropriate for the type of the argument.
298 *
299 * If an exception is thrown during insertion, ios_base::badbit
300 * will be turned on in the stream's error state. If badbit is on in
301 * the stream's exceptions mask, the exception will be rethrown
302 * without completing its actions.
303 */
304
305 /**
306 * @brief Simple insertion.
307 * @param __c The character to insert.
308 * @return *this
309 *
310 * Tries to insert @p __c.
311 *
312 * @note This function is not overloaded on signed char and
313 * unsigned char.
314 */
315 __ostream_type&
316 put(char_type __c);
317
318 /**
319 * @brief Core write functionality, without sentry.
320 * @param __s The array to insert.
321 * @param __n Maximum number of characters to insert.
322 */
323 void
324 _M_write(const char_type* __s, streamsize __n)
325 {
326 const streamsize __put = this->rdbuf()->sputn(__s, __n);
327 if (__put != __n)
328 this->setstate(ios_base::badbit);
329 }
330
331 /**
332 * @brief Character string insertion.
333 * @param __s The array to insert.
334 * @param __n Maximum number of characters to insert.
335 * @return *this
336 *
337 * Characters are copied from @p __s and inserted into the stream until
338 * one of the following happens:
339 *
340 * - @p __n characters are inserted
341 * - inserting into the output sequence fails (in this case, badbit
342 * will be set in the stream's error state)
343 *
344 * @note This function is not overloaded on signed char and
345 * unsigned char.
346 */
347 __ostream_type&
348 write(const char_type* __s, streamsize __n);
349 ///@}
350
351 /**
352 * @brief Synchronizing the stream buffer.
353 * @return *this
354 *
355 * If @c rdbuf() is a null pointer, changes nothing.
356 *
357 * Otherwise, calls @c rdbuf()->pubsync(), and if that returns -1,
358 * sets badbit.
359 */
360 __ostream_type&
361 flush();
362
363 /**
364 * @brief Getting the current write position.
365 * @return A file position object.
366 *
367 * If @c fail() is not false, returns @c pos_type(-1) to indicate
368 * failure. Otherwise returns @c rdbuf()->pubseekoff(0,cur,out).
369 */
370 pos_type
371 tellp();
372
373 /**
374 * @brief Changing the current write position.
375 * @param __pos A file position object.
376 * @return *this
377 *
378 * If @c fail() is not true, calls @c rdbuf()->pubseekpos(pos). If
379 * that function fails, sets failbit.
380 */
381 __ostream_type&
382 seekp(pos_type);
383
384 /**
385 * @brief Changing the current write position.
386 * @param __off A file offset object.
387 * @param __dir The direction in which to seek.
388 * @return *this
389 *
390 * If @c fail() is not true, calls @c rdbuf()->pubseekoff(off,dir).
391 * If that function fails, sets failbit.
392 */
393 __ostream_type&
394 seekp(off_type, ios_base::seekdir);
395
396 protected:
397 basic_ostream()
398 { this->init(0); }
399
400#if __cplusplus >= 201103L
401 // Non-standard constructor that does not call init()
402 basic_ostream(basic_iostream<_CharT, _Traits>&) { }
403
404 basic_ostream(const basic_ostream&) = delete;
405
406 basic_ostream(basic_ostream&& __rhs)
407 : __ios_type()
408 { __ios_type::move(__rhs); }
409
410 // 27.7.3.3 Assign/swap
411
412 basic_ostream& operator=(const basic_ostream&) = delete;
413
414 basic_ostream&
415 operator=(basic_ostream&& __rhs)
416 {
417 swap(__rhs);
418 return *this;
419 }
420
421 void
422 swap(basic_ostream& __rhs)
423 { __ios_type::swap(__rhs); }
424#endif
425
426 template<typename _ValueT>
427 __ostream_type&
428 _M_insert(_ValueT __v);
429 };
430
431 /**
432 * @brief Performs setup work for output streams.
433 *
434 * Objects of this class are created before all of the standard
435 * inserters are run. It is responsible for <em>exception-safe prefix and
436 * suffix operations</em>.
437 */
438 template <typename _CharT, typename _Traits>
439 class basic_ostream<_CharT, _Traits>::sentry
440 {
441 // Data Members.
442 bool _M_ok;
443 basic_ostream<_CharT, _Traits>& _M_os;
444
445 public:
446 /**
447 * @brief The constructor performs preparatory work.
448 * @param __os The output stream to guard.
449 *
450 * If the stream state is good (@a __os.good() is true), then if the
451 * stream is tied to another output stream, @c is.tie()->flush()
452 * is called to synchronize the output sequences.
453 *
454 * If the stream state is still good, then the sentry state becomes
455 * true (@a okay).
456 */
457 explicit
458 sentry(basic_ostream<_CharT, _Traits>& __os);
459
460#pragma GCC diagnostic push
461#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
462 /**
463 * @brief Possibly flushes the stream.
464 *
465 * If @c ios_base::unitbuf is set in @c os.flags(), and
466 * @c std::uncaught_exception() is true, the sentry destructor calls
467 * @c flush() on the output stream.
468 */
469 ~sentry()
470 {
471 // XXX MT
472 if (bool(_M_os.flags() & ios_base::unitbuf) && !uncaught_exception())
473 {
474 // Can't call flush directly or else will get into recursive lock.
475 if (_M_os.rdbuf() && _M_os.rdbuf()->pubsync() == -1)
476 _M_os.setstate(ios_base::badbit);
477 }
478 }
479#pragma GCC diagnostic pop
480
481 /**
482 * @brief Quick status checking.
483 * @return The sentry state.
484 *
485 * For ease of use, sentries may be converted to booleans. The
486 * return value is that of the sentry state (true == okay).
487 */
488#if __cplusplus >= 201103L
489 explicit
490#endif
491 operator bool() const
492 { return _M_ok; }
493 };
494
495 ///@{
496 /**
497 * @brief Character inserters
498 * @param __out An output stream.
499 * @param __c A character.
500 * @return out
501 *
502 * Behaves like one of the formatted arithmetic inserters described in
503 * std::basic_ostream. After constructing a sentry object with good
504 * status, this function inserts a single character and any required
505 * padding (as determined by [22.2.2.2.2]). @c __out.width(0) is then
506 * called.
507 *
508 * If @p __c is of type @c char and the character type of the stream is not
509 * @c char, the character is widened before insertion.
510 */
511 template<typename _CharT, typename _Traits>
512 inline basic_ostream<_CharT, _Traits>&
513 operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
514 { return __ostream_insert(__out, &__c, 1); }
515
516 template<typename _CharT, typename _Traits>
517 inline basic_ostream<_CharT, _Traits>&
518 operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
519 { return (__out << __out.widen(__c)); }
520
521 // Specialization
522 template<typename _Traits>
523 inline basic_ostream<char, _Traits>&
524 operator<<(basic_ostream<char, _Traits>& __out, char __c)
525 { return __ostream_insert(__out, &__c, 1); }
526
527 // Signed and unsigned
528 template<typename _Traits>
529 inline basic_ostream<char, _Traits>&
530 operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
531 { return (__out << static_cast<char>(__c)); }
532
533 template<typename _Traits>
534 inline basic_ostream<char, _Traits>&
535 operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
536 { return (__out << static_cast<char>(__c)); }
537
538#if __cplusplus > 201703L
539 // The following deleted overloads prevent formatting character values as
540 // numeric values.
541
542 template<typename _Traits>
543 basic_ostream<char, _Traits>&
544 operator<<(basic_ostream<char, _Traits>&, wchar_t) = delete;
545
546#ifdef _GLIBCXX_USE_CHAR8_T
547 template<typename _Traits>
548 basic_ostream<char, _Traits>&
549 operator<<(basic_ostream<char, _Traits>&, char8_t) = delete;
550#endif
551
552 template<typename _Traits>
553 basic_ostream<char, _Traits>&
554 operator<<(basic_ostream<char, _Traits>&, char16_t) = delete;
555
556 template<typename _Traits>
557 basic_ostream<char, _Traits>&
558 operator<<(basic_ostream<char, _Traits>&, char32_t) = delete;
559
560#ifdef _GLIBCXX_USE_WCHAR_T
561#ifdef _GLIBCXX_USE_CHAR8_T
562 template<typename _Traits>
563 basic_ostream<wchar_t, _Traits>&
564 operator<<(basic_ostream<wchar_t, _Traits>&, char8_t) = delete;
565#endif // _GLIBCXX_USE_CHAR8_T
566
567 template<typename _Traits>
568 basic_ostream<wchar_t, _Traits>&
569 operator<<(basic_ostream<wchar_t, _Traits>&, char16_t) = delete;
570
571 template<typename _Traits>
572 basic_ostream<wchar_t, _Traits>&
573 operator<<(basic_ostream<wchar_t, _Traits>&, char32_t) = delete;
574#endif // _GLIBCXX_USE_WCHAR_T
575#endif // C++20
576 ///@}
577
578 ///@{
579 /**
580 * @brief String inserters
581 * @param __out An output stream.
582 * @param __s A character string.
583 * @return out
584 * @pre @p __s must be a non-NULL pointer
585 *
586 * Behaves like one of the formatted arithmetic inserters described in
587 * std::basic_ostream. After constructing a sentry object with good
588 * status, this function inserts @c traits::length(__s) characters starting
589 * at @p __s, widened if necessary, followed by any required padding (as
590 * determined by [22.2.2.2.2]). @c __out.width(0) is then called.
591 */
592 template<typename _CharT, typename _Traits>
593 inline basic_ostream<_CharT, _Traits>&
594 operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
595 {
596 if (!__s)
597 __out.setstate(ios_base::badbit);
598 else
599 __ostream_insert(__out, __s,
600 static_cast<streamsize>(_Traits::length(__s)));
601 return __out;
602 }
603
604 template<typename _CharT, typename _Traits>
605 basic_ostream<_CharT, _Traits> &
606 operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s);
607
608 // Partial specializations
609 template<typename _Traits>
610 inline basic_ostream<char, _Traits>&
611 operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
612 {
613 if (!__s)
614 __out.setstate(ios_base::badbit);
615 else
616 __ostream_insert(__out, __s,
617 static_cast<streamsize>(_Traits::length(__s)));
618 return __out;
619 }
620
621 // Signed and unsigned
622 template<typename _Traits>
623 inline basic_ostream<char, _Traits>&
624 operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
625 { return (__out << reinterpret_cast<const char*>(__s)); }
626
627 template<typename _Traits>
628 inline basic_ostream<char, _Traits> &
629 operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
630 { return (__out << reinterpret_cast<const char*>(__s)); }
631
632#if __cplusplus > 201703L
633 // The following deleted overloads prevent formatting strings as
634 // pointer values.
635
636 template<typename _Traits>
637 basic_ostream<char, _Traits>&
638 operator<<(basic_ostream<char, _Traits>&, const wchar_t*) = delete;
639
640#ifdef _GLIBCXX_USE_CHAR8_T
641 template<typename _Traits>
642 basic_ostream<char, _Traits>&
643 operator<<(basic_ostream<char, _Traits>&, const char8_t*) = delete;
644#endif // _GLIBCXX_USE_CHAR8_T
645
646 template<typename _Traits>
647 basic_ostream<char, _Traits>&
648 operator<<(basic_ostream<char, _Traits>&, const char16_t*) = delete;
649
650 template<typename _Traits>
651 basic_ostream<char, _Traits>&
652 operator<<(basic_ostream<char, _Traits>&, const char32_t*) = delete;
653
654#ifdef _GLIBCXX_USE_WCHAR_T
655#ifdef _GLIBCXX_USE_CHAR8_T
656 template<typename _Traits>
657 basic_ostream<wchar_t, _Traits>&
658 operator<<(basic_ostream<wchar_t, _Traits>&, const char8_t*) = delete;
659#endif
660
661 template<typename _Traits>
662 basic_ostream<wchar_t, _Traits>&
663 operator<<(basic_ostream<wchar_t, _Traits>&, const char16_t*) = delete;
664
665 template<typename _Traits>
666 basic_ostream<wchar_t, _Traits>&
667 operator<<(basic_ostream<wchar_t, _Traits>&, const char32_t*) = delete;
668#endif // _GLIBCXX_USE_WCHAR_T
669#endif // C++20
670 ///@}
671
672 // Standard basic_ostream manipulators
673
674 /**
675 * @brief Write a newline and flush the stream.
676 *
677 * This manipulator is often mistakenly used when a simple newline is
678 * desired, leading to poor buffering performance. See
679 * https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
680 * for more on this subject.
681 */
682 template<typename _CharT, typename _Traits>
683 inline basic_ostream<_CharT, _Traits>&
684 endl(basic_ostream<_CharT, _Traits>& __os)
685 { return flush(__os.put(__os.widen('\n'))); }
686
687 /**
688 * @brief Write a null character into the output sequence.
689 *
690 * <em>Null character</em> is @c CharT() by definition. For CharT
691 * of @c char, this correctly writes the ASCII @c NUL character
692 * string terminator.
693 */
694 template<typename _CharT, typename _Traits>
695 inline basic_ostream<_CharT, _Traits>&
696 ends(basic_ostream<_CharT, _Traits>& __os)
697 { return __os.put(_CharT()); }
698
699 /**
700 * @brief Flushes the output stream.
701 *
702 * This manipulator simply calls the stream's @c flush() member function.
703 */
704 template<typename _CharT, typename _Traits>
705 inline basic_ostream<_CharT, _Traits>&
706 flush(basic_ostream<_CharT, _Traits>& __os)
707 { return __os.flush(); }
708
709#if __cplusplus >= 201103L
710 // C++11 27.7.3.9 Rvalue stream insertion [ostream.rvalue]
711 // _GLIBCXX_RESOLVE_LIB_DEFECTS
712 // 1203. More useful rvalue stream insertion
713
714#if __cpp_lib_concepts
715 // Use concepts if possible because they're cheaper to evaluate.
716 template<typename _Tp>
717 concept __derived_from_ios_base = is_class_v<_Tp>
718 && (!is_same_v<_Tp, ios_base>)
719 && requires (_Tp* __t, ios_base* __b) { __b = __t; };
720
721 template<typename _Os, typename _Tp>
722 requires __derived_from_ios_base<_Os>
723 && requires (_Os& __os, const _Tp& __t) { __os << __t; }
724 using __rvalue_stream_insertion_t = _Os&&;
725#else
726 template<typename _Tp>
727 using _Require_derived_from_ios_base
728 = _Require<is_class<_Tp>, __not_<is_same<_Tp, ios_base>>,
729 is_convertible<typename add_pointer<_Tp>::type, ios_base*>>;
730
731 template<typename _Os, typename _Tp,
732 typename = _Require_derived_from_ios_base<_Os>,
733 typename
734 = decltype(std::declval<_Os&>() << std::declval<const _Tp&>())>
735 using __rvalue_stream_insertion_t = _Os&&;
736#endif
737
738 /**
739 * @brief Generic inserter for rvalue stream
740 * @param __os An input stream.
741 * @param __x A reference to the object being inserted.
742 * @return __os
743 *
744 * This is just a forwarding function to allow insertion to
745 * rvalue streams since they won't bind to the inserter functions
746 * that take an lvalue reference.
747 */
748 template<typename _Ostream, typename _Tp>
749 inline __rvalue_stream_insertion_t<_Ostream, _Tp>
750 operator<<(_Ostream&& __os, const _Tp& __x)
751 {
752 __os << __x;
753 return std::move(__os);
754 }
755
756#if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
757 template<typename _CharT, typename _Traits>
758 class __syncbuf_base : public basic_streambuf<_CharT, _Traits>
759 {
760 public:
761 static bool*
762 _S_get(basic_streambuf<_CharT, _Traits>* __buf [[maybe_unused]]) noexcept
763 {
764#if __cpp_rtti
765 if (auto __p = dynamic_cast<__syncbuf_base*>(__buf))
766 return &__p->_M_emit_on_sync;
767#endif
768 return nullptr;
769 }
770
771 protected:
772 __syncbuf_base(basic_streambuf<_CharT, _Traits>* __w = nullptr)
773 : _M_wrapped(__w)
774 { }
775
776 basic_streambuf<_CharT, _Traits>* _M_wrapped = nullptr;
777 bool _M_emit_on_sync = false;
778 bool _M_needs_sync = false;
779 };
780
781 template<typename _CharT, typename _Traits>
782 inline basic_ostream<_CharT, _Traits>&
783 emit_on_flush(basic_ostream<_CharT, _Traits>& __os)
784 {
785 if (bool* __flag = __syncbuf_base<_CharT, _Traits>::_S_get(__os.rdbuf()))
786 *__flag = true;
787 return __os;
788 }
789
790 template<typename _CharT, typename _Traits>
791 inline basic_ostream<_CharT, _Traits>&
792 noemit_on_flush(basic_ostream<_CharT, _Traits>& __os)
793 {
794 if (bool* __flag = __syncbuf_base<_CharT, _Traits>::_S_get(__os.rdbuf()))
795 *__flag = false;
796 return __os;
797 }
798
799 template<typename _CharT, typename _Traits>
800 inline basic_ostream<_CharT, _Traits>&
801 flush_emit(basic_ostream<_CharT, _Traits>& __os)
802 {
803 struct _Restore
804 {
805 ~_Restore() { *_M_flag = _M_prev; }
806
807 bool _M_prev = false;
808 bool* _M_flag = &_M_prev;
809 } __restore;
810
811 if (bool* __flag = __syncbuf_base<_CharT, _Traits>::_S_get(__os.rdbuf()))
812 {
813 __restore._M_prev = *__flag;
814 __restore._M_flag = __flag;
815 *__flag = true;
816 }
817
818 __os.flush();
819 return __os;
820 }
821
822#endif // C++20
823
824#endif // C++11
825
826_GLIBCXX_END_NAMESPACE_VERSION
827} // namespace std
828
829#include <bits/ostream.tcc>
830
831#endif /* _GLIBCXX_OSTREAM */
832

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