xref: /netbsd-src/external/gpl3/gcc/dist/libstdc++-v3/include/std/ostream (revision b1e838363e3c6fc78a55519254d99869742dd33c)
1// Output streams -*- C++ -*-
2
3// Copyright (C) 1997-2022 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  Character string insertion.
320       *  @param  __s  The array to insert.
321       *  @param  __n  Maximum number of characters to insert.
322       *  @return  *this
323       *
324       *  Characters are copied from @p __s and inserted into the stream until
325       *  one of the following happens:
326       *
327       *  - @p __n characters are inserted
328       *  - inserting into the output sequence fails (in this case, badbit
329       *    will be set in the stream's error state)
330       *
331       *  @note  This function is not overloaded on signed char and
332       *         unsigned char.
333      */
334      __ostream_type&
335      write(const char_type* __s, streamsize __n);
336      ///@}
337
338      /**
339       *  @brief  Synchronizing the stream buffer.
340       *  @return  *this
341       *
342       *  If @c rdbuf() is a null pointer, changes nothing.
343       *
344       *  Otherwise, calls @c rdbuf()->pubsync(), and if that returns -1,
345       *  sets badbit.
346      */
347      __ostream_type&
348      flush();
349
350      /**
351       *  @brief  Getting the current write position.
352       *  @return  A file position object.
353       *
354       *  If @c fail() is not false, returns @c pos_type(-1) to indicate
355       *  failure.  Otherwise returns @c rdbuf()->pubseekoff(0,cur,out).
356      */
357      pos_type
358      tellp();
359
360      /**
361       *  @brief  Changing the current write position.
362       *  @param  __pos  A file position object.
363       *  @return  *this
364       *
365       *  If @c fail() is not true, calls @c rdbuf()->pubseekpos(pos).  If
366       *  that function fails, sets failbit.
367      */
368      __ostream_type&
369      seekp(pos_type);
370
371      /**
372       *  @brief  Changing the current write position.
373       *  @param  __off  A file offset object.
374       *  @param  __dir  The direction in which to seek.
375       *  @return  *this
376       *
377       *  If @c fail() is not true, calls @c rdbuf()->pubseekoff(off,dir).
378       *  If that function fails, sets failbit.
379      */
380       __ostream_type&
381      seekp(off_type, ios_base::seekdir);
382
383    protected:
384      basic_ostream()
385      { this->init(0); }
386
387#if __cplusplus >= 201103L
388      // Non-standard constructor that does not call init()
389      basic_ostream(basic_iostream<_CharT, _Traits>&) { }
390
391      basic_ostream(const basic_ostream&) = delete;
392
393      basic_ostream(basic_ostream&& __rhs)
394      : __ios_type()
395      { __ios_type::move(__rhs); }
396
397      // 27.7.3.3 Assign/swap
398
399      basic_ostream& operator=(const basic_ostream&) = delete;
400
401      basic_ostream&
402      operator=(basic_ostream&& __rhs)
403      {
404	swap(__rhs);
405	return *this;
406      }
407
408      void
409      swap(basic_ostream& __rhs)
410      { __ios_type::swap(__rhs); }
411#endif
412
413      template<typename _ValueT>
414	__ostream_type&
415	_M_insert(_ValueT __v);
416
417    private:
418#if !_GLIBCXX_INLINE_VERSION
419      void
420      _M_write(const char_type* __s, streamsize __n)
421      { std::__ostream_insert(*this, __s, __n); }
422#endif
423    };
424
425  /**
426   *  @brief  Performs setup work for output streams.
427   *
428   *  Objects of this class are created before all of the standard
429   *  inserters are run.  It is responsible for <em>exception-safe prefix and
430   *  suffix operations</em>.
431  */
432  template <typename _CharT, typename _Traits>
433    class basic_ostream<_CharT, _Traits>::sentry
434    {
435      // Data Members.
436      bool 				_M_ok;
437      basic_ostream<_CharT, _Traits>& 	_M_os;
438
439    public:
440      /**
441       *  @brief  The constructor performs preparatory work.
442       *  @param  __os  The output stream to guard.
443       *
444       *  If the stream state is good (@a __os.good() is true), then if the
445       *  stream is tied to another output stream, @c is.tie()->flush()
446       *  is called to synchronize the output sequences.
447       *
448       *  If the stream state is still good, then the sentry state becomes
449       *  true (@a okay).
450      */
451      explicit
452      sentry(basic_ostream<_CharT, _Traits>& __os);
453
454#pragma GCC diagnostic push
455#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
456      /**
457       *  @brief  Possibly flushes the stream.
458       *
459       *  If @c ios_base::unitbuf is set in @c os.flags(), and
460       *  @c std::uncaught_exception() is true, the sentry destructor calls
461       *  @c flush() on the output stream.
462      */
463      ~sentry()
464      {
465	// XXX MT
466	if (bool(_M_os.flags() & ios_base::unitbuf) && !uncaught_exception())
467	  {
468	    // Can't call flush directly or else will get into recursive lock.
469	    if (_M_os.rdbuf() && _M_os.rdbuf()->pubsync() == -1)
470	      _M_os.setstate(ios_base::badbit);
471	  }
472      }
473#pragma GCC diagnostic pop
474
475      /**
476       *  @brief  Quick status checking.
477       *  @return  The sentry state.
478       *
479       *  For ease of use, sentries may be converted to booleans.  The
480       *  return value is that of the sentry state (true == okay).
481      */
482#if __cplusplus >= 201103L
483      explicit
484#endif
485      operator bool() const
486      { return _M_ok; }
487    };
488
489  ///@{
490  /**
491   *  @brief  Character inserters
492   *  @param  __out  An output stream.
493   *  @param  __c  A character.
494   *  @return  out
495   *
496   *  Behaves like one of the formatted arithmetic inserters described in
497   *  std::basic_ostream.  After constructing a sentry object with good
498   *  status, this function inserts a single character and any required
499   *  padding (as determined by [22.2.2.2.2]).  @c __out.width(0) is then
500   *  called.
501   *
502   *  If @p __c is of type @c char and the character type of the stream is not
503   *  @c char, the character is widened before insertion.
504  */
505  template<typename _CharT, typename _Traits>
506    inline basic_ostream<_CharT, _Traits>&
507    operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
508    {
509      if (__out.width() != 0)
510	return __ostream_insert(__out, &__c, 1);
511      __out.put(__c);
512      return __out;
513    }
514
515  template<typename _CharT, typename _Traits>
516    inline basic_ostream<_CharT, _Traits>&
517    operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
518    { return (__out << __out.widen(__c)); }
519
520  // Specialization
521  template<typename _Traits>
522    inline basic_ostream<char, _Traits>&
523    operator<<(basic_ostream<char, _Traits>& __out, char __c)
524    {
525      if (__out.width() != 0)
526	return __ostream_insert(__out, &__c, 1);
527      __out.put(__c);
528      return __out;
529    }
530
531  // Signed and unsigned
532  template<typename _Traits>
533    inline basic_ostream<char, _Traits>&
534    operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
535    { return (__out << static_cast<char>(__c)); }
536
537  template<typename _Traits>
538    inline basic_ostream<char, _Traits>&
539    operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
540    { return (__out << static_cast<char>(__c)); }
541
542#if __cplusplus > 201703L
543  // The following deleted overloads prevent formatting character values as
544  // numeric values.
545
546  template<typename _Traits>
547    basic_ostream<char, _Traits>&
548    operator<<(basic_ostream<char, _Traits>&, wchar_t) = delete;
549
550#ifdef _GLIBCXX_USE_CHAR8_T
551  template<typename _Traits>
552    basic_ostream<char, _Traits>&
553    operator<<(basic_ostream<char, _Traits>&, char8_t) = delete;
554#endif
555
556  template<typename _Traits>
557    basic_ostream<char, _Traits>&
558    operator<<(basic_ostream<char, _Traits>&, char16_t) = delete;
559
560  template<typename _Traits>
561    basic_ostream<char, _Traits>&
562    operator<<(basic_ostream<char, _Traits>&, char32_t) = delete;
563
564#ifdef _GLIBCXX_USE_WCHAR_T
565#ifdef _GLIBCXX_USE_CHAR8_T
566  template<typename _Traits>
567    basic_ostream<wchar_t, _Traits>&
568    operator<<(basic_ostream<wchar_t, _Traits>&, char8_t) = delete;
569#endif // _GLIBCXX_USE_CHAR8_T
570
571  template<typename _Traits>
572    basic_ostream<wchar_t, _Traits>&
573    operator<<(basic_ostream<wchar_t, _Traits>&, char16_t) = delete;
574
575  template<typename _Traits>
576    basic_ostream<wchar_t, _Traits>&
577    operator<<(basic_ostream<wchar_t, _Traits>&, char32_t) = delete;
578#endif // _GLIBCXX_USE_WCHAR_T
579#endif // C++20
580  ///@}
581
582  ///@{
583  /**
584   *  @brief  String inserters
585   *  @param  __out  An output stream.
586   *  @param  __s  A character string.
587   *  @return  out
588   *  @pre  @p __s must be a non-NULL pointer
589   *
590   *  Behaves like one of the formatted arithmetic inserters described in
591   *  std::basic_ostream.  After constructing a sentry object with good
592   *  status, this function inserts @c traits::length(__s) characters starting
593   *  at @p __s, widened if necessary, followed by any required padding (as
594   *  determined by [22.2.2.2.2]).  @c __out.width(0) is then called.
595  */
596  template<typename _CharT, typename _Traits>
597    inline basic_ostream<_CharT, _Traits>&
598    operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
599    {
600      if (!__s)
601	__out.setstate(ios_base::badbit);
602      else
603	__ostream_insert(__out, __s,
604			 static_cast<streamsize>(_Traits::length(__s)));
605      return __out;
606    }
607
608  template<typename _CharT, typename _Traits>
609    basic_ostream<_CharT, _Traits> &
610    operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s);
611
612  // Partial specializations
613  template<typename _Traits>
614    inline basic_ostream<char, _Traits>&
615    operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
616    {
617      if (!__s)
618	__out.setstate(ios_base::badbit);
619      else
620	__ostream_insert(__out, __s,
621			 static_cast<streamsize>(_Traits::length(__s)));
622      return __out;
623    }
624
625  // Signed and unsigned
626  template<typename _Traits>
627    inline basic_ostream<char, _Traits>&
628    operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
629    { return (__out << reinterpret_cast<const char*>(__s)); }
630
631  template<typename _Traits>
632    inline basic_ostream<char, _Traits> &
633    operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
634    { return (__out << reinterpret_cast<const char*>(__s)); }
635
636#if __cplusplus > 201703L
637   // The following deleted overloads prevent formatting strings as
638   // pointer values.
639
640  template<typename _Traits>
641    basic_ostream<char, _Traits>&
642    operator<<(basic_ostream<char, _Traits>&, const wchar_t*) = delete;
643
644#ifdef _GLIBCXX_USE_CHAR8_T
645  template<typename _Traits>
646    basic_ostream<char, _Traits>&
647    operator<<(basic_ostream<char, _Traits>&, const char8_t*) = delete;
648#endif // _GLIBCXX_USE_CHAR8_T
649
650  template<typename _Traits>
651    basic_ostream<char, _Traits>&
652    operator<<(basic_ostream<char, _Traits>&, const char16_t*) = delete;
653
654  template<typename _Traits>
655    basic_ostream<char, _Traits>&
656    operator<<(basic_ostream<char, _Traits>&, const char32_t*) = delete;
657
658#ifdef _GLIBCXX_USE_WCHAR_T
659#ifdef _GLIBCXX_USE_CHAR8_T
660  template<typename _Traits>
661    basic_ostream<wchar_t, _Traits>&
662    operator<<(basic_ostream<wchar_t, _Traits>&, const char8_t*) = delete;
663#endif
664
665  template<typename _Traits>
666    basic_ostream<wchar_t, _Traits>&
667    operator<<(basic_ostream<wchar_t, _Traits>&, const char16_t*) = delete;
668
669  template<typename _Traits>
670    basic_ostream<wchar_t, _Traits>&
671    operator<<(basic_ostream<wchar_t, _Traits>&, const char32_t*) = delete;
672#endif // _GLIBCXX_USE_WCHAR_T
673#endif // C++20
674  ///@}
675
676  // Standard basic_ostream manipulators
677
678  /**
679   *  @brief  Write a newline and flush the stream.
680   *
681   *  This manipulator is often mistakenly used when a simple newline is
682   *  desired, leading to poor buffering performance.  See
683   *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
684   *  for more on this subject.
685  */
686  template<typename _CharT, typename _Traits>
687    inline basic_ostream<_CharT, _Traits>&
688    endl(basic_ostream<_CharT, _Traits>& __os)
689    { return flush(__os.put(__os.widen('\n'))); }
690
691  /**
692   *  @brief  Write a null character into the output sequence.
693   *
694   *  <em>Null character</em> is @c CharT() by definition.  For CharT
695   *  of @c char, this correctly writes the ASCII @c NUL character
696   *  string terminator.
697  */
698  template<typename _CharT, typename _Traits>
699    inline basic_ostream<_CharT, _Traits>&
700    ends(basic_ostream<_CharT, _Traits>& __os)
701    { return __os.put(_CharT()); }
702
703  /**
704   *  @brief  Flushes the output stream.
705   *
706   *  This manipulator simply calls the stream's @c flush() member function.
707  */
708  template<typename _CharT, typename _Traits>
709    inline basic_ostream<_CharT, _Traits>&
710    flush(basic_ostream<_CharT, _Traits>& __os)
711    { return __os.flush(); }
712
713#if __cplusplus >= 201103L
714  // C++11 27.7.3.9 Rvalue stream insertion [ostream.rvalue]
715  // _GLIBCXX_RESOLVE_LIB_DEFECTS
716  // 1203. More useful rvalue stream insertion
717
718#if __cpp_lib_concepts
719  // Use concepts if possible because they're cheaper to evaluate.
720  template<typename _Tp>
721    concept __derived_from_ios_base = is_class_v<_Tp>
722      && (!is_same_v<_Tp, ios_base>)
723      && requires (_Tp* __t, ios_base* __b) { __b = __t; };
724
725  template<typename _Os, typename _Tp>
726    requires __derived_from_ios_base<_Os>
727      && requires (_Os& __os, const _Tp& __t) { __os << __t; }
728    using __rvalue_stream_insertion_t = _Os&&;
729#else
730  template<typename _Tp>
731    using _Require_derived_from_ios_base
732      = _Require<is_class<_Tp>, __not_<is_same<_Tp, ios_base>>,
733		 is_convertible<typename add_pointer<_Tp>::type, ios_base*>>;
734
735  template<typename _Os, typename _Tp,
736	   typename = _Require_derived_from_ios_base<_Os>,
737	   typename
738	     = decltype(std::declval<_Os&>() << std::declval<const _Tp&>())>
739    using __rvalue_stream_insertion_t = _Os&&;
740#endif
741
742  /**
743   *  @brief  Generic inserter for rvalue stream
744   *  @param  __os  An input stream.
745   *  @param  __x  A reference to the object being inserted.
746   *  @return  __os
747   *
748   *  This is just a forwarding function to allow insertion to
749   *  rvalue streams since they won't bind to the inserter functions
750   *  that take an lvalue reference.
751  */
752  template<typename _Ostream, typename _Tp>
753    inline __rvalue_stream_insertion_t<_Ostream, _Tp>
754    operator<<(_Ostream&& __os, const _Tp& __x)
755    {
756      __os << __x;
757      return std::move(__os);
758    }
759
760#if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
761  template<typename _CharT, typename _Traits>
762    class __syncbuf_base : public basic_streambuf<_CharT, _Traits>
763    {
764    public:
765      static bool*
766      _S_get(basic_streambuf<_CharT, _Traits>* __buf [[maybe_unused]]) noexcept
767      {
768#if __cpp_rtti
769	if (auto __p = dynamic_cast<__syncbuf_base*>(__buf))
770	  return &__p->_M_emit_on_sync;
771#endif
772	return nullptr;
773      }
774
775    protected:
776      __syncbuf_base(basic_streambuf<_CharT, _Traits>* __w = nullptr)
777      : _M_wrapped(__w)
778      { }
779
780      basic_streambuf<_CharT, _Traits>* _M_wrapped = nullptr;
781      bool _M_emit_on_sync = false;
782      bool _M_needs_sync = false;
783    };
784
785  template<typename _CharT, typename _Traits>
786    inline basic_ostream<_CharT, _Traits>&
787    emit_on_flush(basic_ostream<_CharT, _Traits>& __os)
788    {
789      if (bool* __flag = __syncbuf_base<_CharT, _Traits>::_S_get(__os.rdbuf()))
790	*__flag = true;
791      return __os;
792    }
793
794  template<typename _CharT, typename _Traits>
795    inline basic_ostream<_CharT, _Traits>&
796    noemit_on_flush(basic_ostream<_CharT, _Traits>& __os)
797    {
798      if (bool* __flag = __syncbuf_base<_CharT, _Traits>::_S_get(__os.rdbuf()))
799	*__flag = false;
800      return __os;
801    }
802
803  template<typename _CharT, typename _Traits>
804    inline basic_ostream<_CharT, _Traits>&
805    flush_emit(basic_ostream<_CharT, _Traits>& __os)
806    {
807      struct _Restore
808      {
809	~_Restore() { *_M_flag = _M_prev; }
810
811	bool _M_prev = false;
812	bool* _M_flag = &_M_prev;
813      } __restore;
814
815      if (bool* __flag = __syncbuf_base<_CharT, _Traits>::_S_get(__os.rdbuf()))
816	{
817	  __restore._M_prev = *__flag;
818	  __restore._M_flag = __flag;
819	  *__flag = true;
820	}
821
822      __os.flush();
823      return __os;
824    }
825
826#endif // C++20
827
828#endif // C++11
829
830_GLIBCXX_END_NAMESPACE_VERSION
831} // namespace std
832
833#include <bits/ostream.tcc>
834
835#endif	/* _GLIBCXX_OSTREAM */
836