libstdc++
istream
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1 // Input streams -*- C++ -*-
2 
3 // Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
4 // 2006, 2007, 2008, 2009
5 // Free Software Foundation, Inc.
6 //
7 // This file is part of the GNU ISO C++ Library. This library is free
8 // software; you can redistribute it and/or modify it under the
9 // terms of the GNU General Public License as published by the
10 // Free Software Foundation; either version 3, or (at your option)
11 // any later version.
12 
13 // This library is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 // GNU General Public License for more details.
17 
18 // Under Section 7 of GPL version 3, you are granted additional
19 // permissions described in the GCC Runtime Library Exception, version
20 // 3.1, as published by the Free Software Foundation.
21 
22 // You should have received a copy of the GNU General Public License and
23 // a copy of the GCC Runtime Library Exception along with this program;
24 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
25 // <http://www.gnu.org/licenses/>.
26 
27 //
28 // ISO C++ 14882: 27.6.1 Input streams
29 //
30 
31 /** @file istream
32  * This is a Standard C++ Library header.
33  */
34 
35 #ifndef _GLIBCXX_ISTREAM
36 #define _GLIBCXX_ISTREAM 1
37 
38 #pragma GCC system_header
39 
40 #include <ios>
41 #include <ostream>
42 
43 _GLIBCXX_BEGIN_NAMESPACE(std)
44 
45  // [27.6.1.1] Template class basic_istream
46  /**
47  * @brief Controlling input.
48  * @ingroup io
49  *
50  * This is the base class for all input streams. It provides text
51  * formatting of all builtin types, and communicates with any class
52  * derived from basic_streambuf to do the actual input.
53  */
54  template<typename _CharT, typename _Traits>
55  class basic_istream : virtual public basic_ios<_CharT, _Traits>
56  {
57  public:
58  // Types (inherited from basic_ios (27.4.4)):
59  typedef _CharT char_type;
60  typedef typename _Traits::int_type int_type;
61  typedef typename _Traits::pos_type pos_type;
62  typedef typename _Traits::off_type off_type;
63  typedef _Traits traits_type;
64 
65  // Non-standard Types:
72 
73  protected:
74  // Data Members:
75  /**
76  * The number of characters extracted in the previous unformatted
77  * function; see gcount().
78  */
80 
81  public:
82  // [27.6.1.1.1] constructor/destructor
83  /**
84  * @brief Base constructor.
85  *
86  * This ctor is almost never called by the user directly, rather from
87  * derived classes' initialization lists, which pass a pointer to
88  * their own stream buffer.
89  */
90  explicit
91  basic_istream(__streambuf_type* __sb)
92  : _M_gcount(streamsize(0))
93  { this->init(__sb); }
94 
95  /**
96  * @brief Base destructor.
97  *
98  * This does very little apart from providing a virtual base dtor.
99  */
100  virtual
102  { _M_gcount = streamsize(0); }
103 
104  // [27.6.1.1.2] prefix/suffix
105  class sentry;
106  friend class sentry;
107 
108  // [27.6.1.2] formatted input
109  // [27.6.1.2.3] basic_istream::operator>>
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 "std::cin >> std::ws". For more
116  * information, see the iomanip header.
117  */
118  __istream_type&
119  operator>>(__istream_type& (*__pf)(__istream_type&))
120  { return __pf(*this); }
121 
122  __istream_type&
123  operator>>(__ios_type& (*__pf)(__ios_type&))
124  {
125  __pf(*this);
126  return *this;
127  }
128 
129  __istream_type&
131  {
132  __pf(*this);
133  return *this;
134  }
135  //@}
136 
137  // [27.6.1.2.2] arithmetic extractors
138  /**
139  * @name Arithmetic Extractors
140  *
141  * All the @c operator>> functions (aka <em>formatted input
142  * functions</em>) have some common behavior. Each starts by
143  * constructing a temporary object of type std::basic_istream::sentry
144  * with the second argument (noskipws) set to false. This has several
145  * effects, concluding with the setting of a status flag; see the
146  * sentry documentation for more.
147  *
148  * If the sentry status is good, the function tries to extract
149  * whatever data is appropriate for the type of the argument.
150  *
151  * If an exception is thrown during extraction, ios_base::badbit
152  * will be turned on in the stream's error state without causing an
153  * ios_base::failure to be thrown. The original exception will then
154  * be rethrown.
155  */
156  //@{
157  /**
158  * @brief Basic arithmetic extractors
159  * @param A variable of builtin 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 parse the input data.
164  */
165  __istream_type&
166  operator>>(bool& __n)
167  { return _M_extract(__n); }
168 
169  __istream_type&
170  operator>>(short& __n);
171 
172  __istream_type&
173  operator>>(unsigned short& __n)
174  { return _M_extract(__n); }
175 
176  __istream_type&
177  operator>>(int& __n);
178 
179  __istream_type&
180  operator>>(unsigned int& __n)
181  { return _M_extract(__n); }
182 
183  __istream_type&
184  operator>>(long& __n)
185  { return _M_extract(__n); }
186 
187  __istream_type&
188  operator>>(unsigned long& __n)
189  { return _M_extract(__n); }
190 
191 #ifdef _GLIBCXX_USE_LONG_LONG
192  __istream_type&
193  operator>>(long long& __n)
194  { return _M_extract(__n); }
195 
196  __istream_type&
197  operator>>(unsigned long long& __n)
198  { return _M_extract(__n); }
199 #endif
200 
201  __istream_type&
202  operator>>(float& __f)
203  { return _M_extract(__f); }
204 
205  __istream_type&
206  operator>>(double& __f)
207  { return _M_extract(__f); }
208 
209  __istream_type&
210  operator>>(long double& __f)
211  { return _M_extract(__f); }
212 
213  __istream_type&
214  operator>>(void*& __p)
215  { return _M_extract(__p); }
216 
217  /**
218  * @brief Extracting into another streambuf.
219  * @param sb A pointer to a streambuf
220  *
221  * This function behaves like one of the basic arithmetic extractors,
222  * in that it also constructs a sentry object and has the same error
223  * handling behavior.
224  *
225  * If @a sb is NULL, the stream will set failbit in its error state.
226  *
227  * Characters are extracted from this stream and inserted into the
228  * @a sb streambuf until one of the following occurs:
229  *
230  * - the input stream reaches end-of-file,
231  * - insertion into the output buffer fails (in this case, the
232  * character that would have been inserted is not extracted), or
233  * - an exception occurs (and in this case is caught)
234  *
235  * If the function inserts no characters, failbit is set.
236  */
237  __istream_type&
238  operator>>(__streambuf_type* __sb);
239  //@}
240 
241  // [27.6.1.3] unformatted input
242  /**
243  * @brief Character counting
244  * @return The number of characters extracted by the previous
245  * unformatted input function dispatched for this stream.
246  */
247  streamsize
248  gcount() const
249  { return _M_gcount; }
250 
251  /**
252  * @name Unformatted Input Functions
253  *
254  * All the unformatted input functions have some common behavior.
255  * Each starts by constructing a temporary object of type
256  * std::basic_istream::sentry with the second argument (noskipws)
257  * set to true. This has several effects, concluding with the
258  * setting of a status flag; see the sentry documentation for more.
259  *
260  * If the sentry status is good, the function tries to extract
261  * whatever data is appropriate for the type of the argument.
262  *
263  * The number of characters extracted is stored for later retrieval
264  * by gcount().
265  *
266  * If an exception is thrown during extraction, ios_base::badbit
267  * will be turned on in the stream's error state without causing an
268  * ios_base::failure to be thrown. The original exception will then
269  * be rethrown.
270  */
271  //@{
272  /**
273  * @brief Simple extraction.
274  * @return A character, or eof().
275  *
276  * Tries to extract a character. If none are available, sets failbit
277  * and returns traits::eof().
278  */
279  int_type
280  get();
281 
282  /**
283  * @brief Simple extraction.
284  * @param c The character in which to store data.
285  * @return *this
286  *
287  * Tries to extract a character and store it in @a c. If none are
288  * available, sets failbit and returns traits::eof().
289  *
290  * @note This function is not overloaded on signed char and
291  * unsigned char.
292  */
293  __istream_type&
294  get(char_type& __c);
295 
296  /**
297  * @brief Simple multiple-character extraction.
298  * @param s Pointer to an array.
299  * @param n Maximum number of characters to store in @a s.
300  * @param delim A "stop" character.
301  * @return *this
302  *
303  * Characters are extracted and stored into @a s until one of the
304  * following happens:
305  *
306  * - @c n-1 characters are stored
307  * - the input sequence reaches EOF
308  * - the next character equals @a delim, in which case the character
309  * is not extracted
310  *
311  * If no characters are stored, failbit is set in the stream's error
312  * state.
313  *
314  * In any case, a null character is stored into the next location in
315  * the array.
316  *
317  * @note This function is not overloaded on signed char and
318  * unsigned char.
319  */
320  __istream_type&
321  get(char_type* __s, streamsize __n, char_type __delim);
322 
323  /**
324  * @brief Simple multiple-character extraction.
325  * @param s Pointer to an array.
326  * @param n Maximum number of characters to store in @a s.
327  * @return *this
328  *
329  * Returns @c get(s,n,widen('\n')).
330  */
331  __istream_type&
332  get(char_type* __s, streamsize __n)
333  { return this->get(__s, __n, this->widen('\n')); }
334 
335  /**
336  * @brief Extraction into another streambuf.
337  * @param sb A streambuf in which to store data.
338  * @param delim A "stop" character.
339  * @return *this
340  *
341  * Characters are extracted and inserted into @a sb until one of the
342  * following happens:
343  *
344  * - the input sequence reaches EOF
345  * - insertion into the output buffer fails (in this case, the
346  * character that would have been inserted is not extracted)
347  * - the next character equals @a delim (in this case, the character
348  * is not extracted)
349  * - an exception occurs (and in this case is caught)
350  *
351  * If no characters are stored, failbit is set in the stream's error
352  * state.
353  */
354  __istream_type&
355  get(__streambuf_type& __sb, char_type __delim);
356 
357  /**
358  * @brief Extraction into another streambuf.
359  * @param sb A streambuf in which to store data.
360  * @return *this
361  *
362  * Returns @c get(sb,widen('\n')).
363  */
364  __istream_type&
365  get(__streambuf_type& __sb)
366  { return this->get(__sb, this->widen('\n')); }
367 
368  /**
369  * @brief String extraction.
370  * @param s A character array in which to store the data.
371  * @param n Maximum number of characters to extract.
372  * @param delim A "stop" character.
373  * @return *this
374  *
375  * Extracts and stores characters into @a s until one of the
376  * following happens. Note that these criteria are required to be
377  * tested in the order listed here, to allow an input line to exactly
378  * fill the @a s array without setting failbit.
379  *
380  * -# the input sequence reaches end-of-file, in which case eofbit
381  * is set in the stream error state
382  * -# the next character equals @c delim, in which case the character
383  * is extracted (and therefore counted in @c gcount()) but not stored
384  * -# @c n-1 characters are stored, in which case failbit is set
385  * in the stream error state
386  *
387  * If no characters are extracted, failbit is set. (An empty line of
388  * input should therefore not cause failbit to be set.)
389  *
390  * In any case, a null character is stored in the next location in
391  * the array.
392  */
393  __istream_type&
394  getline(char_type* __s, streamsize __n, char_type __delim);
395 
396  /**
397  * @brief String extraction.
398  * @param s A character array in which to store the data.
399  * @param n Maximum number of characters to extract.
400  * @return *this
401  *
402  * Returns @c getline(s,n,widen('\n')).
403  */
404  __istream_type&
405  getline(char_type* __s, streamsize __n)
406  { return this->getline(__s, __n, this->widen('\n')); }
407 
408  /**
409  * @brief Discarding characters
410  * @param n Number of characters to discard.
411  * @param delim A "stop" character.
412  * @return *this
413  *
414  * Extracts characters and throws them away until one of the
415  * following happens:
416  * - if @a n @c != @c std::numeric_limits<int>::max(), @a n
417  * characters are extracted
418  * - the input sequence reaches end-of-file
419  * - the next character equals @a delim (in this case, the character
420  * is extracted); note that this condition will never occur if
421  * @a delim equals @c traits::eof().
422  *
423  * NB: Provide three overloads, instead of the single function
424  * (with defaults) mandated by the Standard: this leads to a
425  * better performing implementation, while still conforming to
426  * the Standard.
427  */
428  __istream_type&
429  ignore();
430 
431  __istream_type&
432  ignore(streamsize __n);
433 
434  __istream_type&
435  ignore(streamsize __n, int_type __delim);
436 
437  /**
438  * @brief Looking ahead in the stream
439  * @return The next character, or eof().
440  *
441  * If, after constructing the sentry object, @c good() is false,
442  * returns @c traits::eof(). Otherwise reads but does not extract
443  * the next input character.
444  */
445  int_type
446  peek();
447 
448  /**
449  * @brief Extraction without delimiters.
450  * @param s A character array.
451  * @param n Maximum number of characters to store.
452  * @return *this
453  *
454  * If the stream state is @c good(), extracts characters and stores
455  * them into @a s until one of the following happens:
456  * - @a n characters are stored
457  * - the input sequence reaches end-of-file, in which case the error
458  * state is set to @c failbit|eofbit.
459  *
460  * @note This function is not overloaded on signed char and
461  * unsigned char.
462  */
463  __istream_type&
464  read(char_type* __s, streamsize __n);
465 
466  /**
467  * @brief Extraction until the buffer is exhausted, but no more.
468  * @param s A character array.
469  * @param n Maximum number of characters to store.
470  * @return The number of characters extracted.
471  *
472  * Extracts characters and stores them into @a s depending on the
473  * number of characters remaining in the streambuf's buffer,
474  * @c rdbuf()->in_avail(), called @c A here:
475  * - if @c A @c == @c -1, sets eofbit and extracts no characters
476  * - if @c A @c == @c 0, extracts no characters
477  * - if @c A @c > @c 0, extracts @c min(A,n)
478  *
479  * The goal is to empty the current buffer, and to not request any
480  * more from the external input sequence controlled by the streambuf.
481  */
482  streamsize
483  readsome(char_type* __s, streamsize __n);
484 
485  /**
486  * @brief Unextracting a single character.
487  * @param c The character to push back into the input stream.
488  * @return *this
489  *
490  * If @c rdbuf() is not null, calls @c rdbuf()->sputbackc(c).
491  *
492  * If @c rdbuf() is null or if @c sputbackc() fails, sets badbit in
493  * the error state.
494  *
495  * @note Since no characters are extracted, the next call to
496  * @c gcount() will return 0, as required by DR 60.
497  */
498  __istream_type&
499  putback(char_type __c);
500 
501  /**
502  * @brief Unextracting the previous character.
503  * @return *this
504  *
505  * If @c rdbuf() is not null, calls @c rdbuf()->sungetc(c).
506  *
507  * If @c rdbuf() is null or if @c sungetc() fails, sets badbit in
508  * the error state.
509  *
510  * @note Since no characters are extracted, the next call to
511  * @c gcount() will return 0, as required by DR 60.
512  */
513  __istream_type&
514  unget();
515 
516  /**
517  * @brief Synchronizing the stream buffer.
518  * @return 0 on success, -1 on failure
519  *
520  * If @c rdbuf() is a null pointer, returns -1.
521  *
522  * Otherwise, calls @c rdbuf()->pubsync(), and if that returns -1,
523  * sets badbit and returns -1.
524  *
525  * Otherwise, returns 0.
526  *
527  * @note This function does not count the number of characters
528  * extracted, if any, and therefore does not affect the next
529  * call to @c gcount().
530  */
531  int
532  sync();
533 
534  /**
535  * @brief Getting the current read position.
536  * @return A file position object.
537  *
538  * If @c fail() is not false, returns @c pos_type(-1) to indicate
539  * failure. Otherwise returns @c rdbuf()->pubseekoff(0,cur,in).
540  *
541  * @note This function does not count the number of characters
542  * extracted, if any, and therefore does not affect the next
543  * call to @c gcount().
544  */
545  pos_type
546  tellg();
547 
548  /**
549  * @brief Changing the current read position.
550  * @param pos A file position object.
551  * @return *this
552  *
553  * If @c fail() is not true, calls @c rdbuf()->pubseekpos(pos). If
554  * that function fails, sets failbit.
555  *
556  * @note This function does not count the number of characters
557  * extracted, if any, and therefore does not affect the next
558  * call to @c gcount().
559  */
560  __istream_type&
561  seekg(pos_type);
562 
563  /**
564  * @brief Changing the current read position.
565  * @param off A file offset object.
566  * @param dir The direction in which to seek.
567  * @return *this
568  *
569  * If @c fail() is not true, calls @c rdbuf()->pubseekoff(off,dir).
570  * If that function fails, sets failbit.
571  *
572  * @note This function does not count the number of characters
573  * extracted, if any, and therefore does not affect the next
574  * call to @c gcount().
575  */
576  __istream_type&
577  seekg(off_type, ios_base::seekdir);
578  //@}
579 
580  protected:
581  basic_istream()
582  : _M_gcount(streamsize(0))
583  { this->init(0); }
584 
585  template<typename _ValueT>
586  __istream_type&
587  _M_extract(_ValueT& __v);
588  };
589 
590  // Explicit specialization declarations, defined in src/istream.cc.
591  template<>
592  basic_istream<char>&
593  basic_istream<char>::
594  getline(char_type* __s, streamsize __n, char_type __delim);
595 
596  template<>
597  basic_istream<char>&
598  basic_istream<char>::
599  ignore(streamsize __n);
600 
601  template<>
602  basic_istream<char>&
603  basic_istream<char>::
604  ignore(streamsize __n, int_type __delim);
605 
606 #ifdef _GLIBCXX_USE_WCHAR_T
607  template<>
608  basic_istream<wchar_t>&
609  basic_istream<wchar_t>::
610  getline(char_type* __s, streamsize __n, char_type __delim);
611 
612  template<>
613  basic_istream<wchar_t>&
614  basic_istream<wchar_t>::
615  ignore(streamsize __n);
616 
617  template<>
618  basic_istream<wchar_t>&
619  basic_istream<wchar_t>::
620  ignore(streamsize __n, int_type __delim);
621 #endif
622 
623  /**
624  * @brief Performs setup work for input streams.
625  *
626  * Objects of this class are created before all of the standard
627  * extractors are run. It is responsible for "exception-safe prefix and
628  * suffix operations," although only prefix actions are currently required
629  * by the standard.
630  */
631  template<typename _CharT, typename _Traits>
632  class basic_istream<_CharT, _Traits>::sentry
633  {
634  public:
635  /// Easy access to dependant types.
636  typedef _Traits traits_type;
637  typedef basic_streambuf<_CharT, _Traits> __streambuf_type;
638  typedef basic_istream<_CharT, _Traits> __istream_type;
639  typedef typename __istream_type::__ctype_type __ctype_type;
640  typedef typename _Traits::int_type __int_type;
641 
642  /**
643  * @brief The constructor performs all the work.
644  * @param is The input stream to guard.
645  * @param noskipws Whether to consume whitespace or not.
646  *
647  * If the stream state is good (@a is.good() is true), then the
648  * following actions are performed, otherwise the sentry state is
649  * false ("not okay") and failbit is set in the stream state.
650  *
651  * The sentry's preparatory actions are:
652  *
653  * -# if the stream is tied to an output stream, @c is.tie()->flush()
654  * is called to synchronize the output sequence
655  * -# if @a noskipws is false, and @c ios_base::skipws is set in
656  * @c is.flags(), the sentry extracts and discards whitespace
657  * characters from the stream. The currently imbued locale is
658  * used to determine whether each character is whitespace.
659  *
660  * If the stream state is still good, then the sentry state becomes
661  * true ("okay").
662  */
663  explicit
664  sentry(basic_istream<_CharT, _Traits>& __is, bool __noskipws = false);
665 
666  /**
667  * @brief Quick status checking.
668  * @return The sentry state.
669  *
670  * For ease of use, sentries may be converted to booleans. The
671  * return value is that of the sentry state (true == okay).
672  */
673  operator bool() const
674  { return _M_ok; }
675 
676  private:
677  bool _M_ok;
678  };
679 
680  // [27.6.1.2.3] character extraction templates
681  //@{
682  /**
683  * @brief Character extractors
684  * @param in An input stream.
685  * @param c A character reference.
686  * @return in
687  *
688  * Behaves like one of the formatted arithmetic extractors described in
689  * std::basic_istream. After constructing a sentry object with good
690  * status, this function extracts a character (if one is available) and
691  * stores it in @a c. Otherwise, sets failbit in the input stream.
692  */
693  template<typename _CharT, typename _Traits>
695  operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c);
696 
697  template<class _Traits>
699  operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
700  { return (__in >> reinterpret_cast<char&>(__c)); }
701 
702  template<class _Traits>
703  inline basic_istream<char, _Traits>&
704  operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
705  { return (__in >> reinterpret_cast<char&>(__c)); }
706  //@}
707 
708  //@{
709  /**
710  * @brief Character string extractors
711  * @param in An input stream.
712  * @param s A pointer to a character array.
713  * @return in
714  *
715  * Behaves like one of the formatted arithmetic extractors described in
716  * std::basic_istream. After constructing a sentry object with good
717  * status, this function extracts up to @c n characters and stores them
718  * into the array starting at @a s. @c n is defined as:
719  *
720  * - if @c width() is greater than zero, @c n is width()
721  * - otherwise @c n is "the number of elements of the largest array of
722  * @c char_type that can store a terminating @c eos." [27.6.1.2.3]/6
723  *
724  * Characters are extracted and stored until one of the following happens:
725  * - @c n-1 characters are stored
726  * - EOF is reached
727  * - the next character is whitespace according to the current locale
728  * - the next character is a null byte (i.e., @c charT() )
729  *
730  * @c width(0) is then called for the input stream.
731  *
732  * If no characters are extracted, sets failbit.
733  */
734  template<typename _CharT, typename _Traits>
735  basic_istream<_CharT, _Traits>&
736  operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s);
737 
738  // Explicit specialization declaration, defined in src/istream.cc.
739  template<>
740  basic_istream<char>&
741  operator>>(basic_istream<char>& __in, char* __s);
742 
743  template<class _Traits>
744  inline basic_istream<char, _Traits>&
745  operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
746  { return (__in >> reinterpret_cast<char*>(__s)); }
747 
748  template<class _Traits>
749  inline basic_istream<char, _Traits>&
750  operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
751  { return (__in >> reinterpret_cast<char*>(__s)); }
752  //@}
753 
754  // 27.6.1.5 Template class basic_iostream
755  /**
756  * @brief Merging istream and ostream capabilities.
757  * @ingroup io
758  *
759  * This class multiply inherits from the input and output stream classes
760  * simply to provide a single interface.
761  */
762  template<typename _CharT, typename _Traits>
764  : public basic_istream<_CharT, _Traits>,
765  public basic_ostream<_CharT, _Traits>
766  {
767  public:
768  // _GLIBCXX_RESOLVE_LIB_DEFECTS
769  // 271. basic_iostream missing typedefs
770  // Types (inherited):
771  typedef _CharT char_type;
772  typedef typename _Traits::int_type int_type;
773  typedef typename _Traits::pos_type pos_type;
774  typedef typename _Traits::off_type off_type;
775  typedef _Traits traits_type;
776 
777  // Non-standard Types:
778  typedef basic_istream<_CharT, _Traits> __istream_type;
780 
781  /**
782  * @brief Constructor does nothing.
783  *
784  * Both of the parent classes are initialized with the same
785  * streambuf pointer passed to this constructor.
786  */
787  explicit
789  : __istream_type(__sb), __ostream_type(__sb) { }
790 
791  /**
792  * @brief Destructor does nothing.
793  */
794  virtual
796 
797  protected:
799  : __istream_type(), __ostream_type() { }
800  };
801 
802  // [27.6.1.4] standard basic_istream manipulators
803  /**
804  * @brief Quick and easy way to eat whitespace
805  *
806  * This manipulator extracts whitespace characters, stopping when the
807  * next character is non-whitespace, or when the input sequence is empty.
808  * If the sequence is empty, @c eofbit is set in the stream, but not
809  * @c failbit.
810  *
811  * The current locale is used to distinguish whitespace characters.
812  *
813  * Example:
814  * @code
815  * MyClass mc;
816  *
817  * std::cin >> std::ws >> mc;
818  * @endcode
819  * will skip leading whitespace before calling operator>> on cin and your
820  * object. Note that the same effect can be achieved by creating a
821  * std::basic_istream::sentry inside your definition of operator>>.
822  */
823  template<typename _CharT, typename _Traits>
824  basic_istream<_CharT, _Traits>&
825  ws(basic_istream<_CharT, _Traits>& __is);
826 
827 _GLIBCXX_END_NAMESPACE
828 
829 #ifndef _GLIBCXX_EXPORT_TEMPLATE
830 # include <bits/istream.tcc>
831 #endif
832 
833 #endif /* _GLIBCXX_ISTREAM */