libstdc++
pointer.h
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1 // Custom pointer adapter and sample storage policies
2 
3 // Copyright (C) 2008-2018 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  * @file ext/pointer.h
27  * This file is a GNU extension to the Standard C++ Library.
28  *
29  * @author Bob Walters
30  *
31  * Provides reusable _Pointer_adapter for assisting in the development of
32  * custom pointer types that can be used with the standard containers via
33  * the allocator::pointer and allocator::const_pointer typedefs.
34  */
35 
36 #ifndef _POINTER_H
37 #define _POINTER_H 1
38 
39 #pragma GCC system_header
40 
41 #include <iosfwd>
43 #include <ext/cast.h>
44 #include <ext/type_traits.h>
45 #if __cplusplus >= 201103L
46 # include <bits/move.h>
47 # include <bits/ptr_traits.h>
48 #endif
49 
50 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
51 {
52 _GLIBCXX_BEGIN_NAMESPACE_VERSION
53 
54  /**
55  * @brief A storage policy for use with _Pointer_adapter<> which yields a
56  * standard pointer.
57  *
58  * A _Storage_policy is required to provide 4 things:
59  * 1) A get() API for returning the stored pointer value.
60  * 2) An set() API for storing a pointer value.
61  * 3) An element_type typedef to define the type this points to.
62  * 4) An operator<() to support pointer comparison.
63  * 5) An operator==() to support pointer comparison.
64  */
65  template<typename _Tp>
67  {
68  public:
69  // the type this pointer points to.
70  typedef _Tp element_type;
71 
72  // A method to fetch the pointer value as a standard T* value;
73  inline _Tp*
74  get() const
75  { return _M_value; }
76 
77  // A method to set the pointer value, from a standard T* value;
78  inline void
79  set(element_type* __arg)
80  { _M_value = __arg; }
81 
82  // Comparison of pointers
83  inline bool
84  operator<(const _Std_pointer_impl& __rarg) const
85  { return (_M_value < __rarg._M_value); }
86 
87  inline bool
88  operator==(const _Std_pointer_impl& __rarg) const
89  { return (_M_value == __rarg._M_value); }
90 
91  private:
92  element_type* _M_value;
93  };
94 
95  /**
96  * @brief A storage policy for use with _Pointer_adapter<> which stores
97  * the pointer's address as an offset value which is relative to
98  * its own address.
99  *
100  * This is intended for pointers within shared memory regions which
101  * might be mapped at different addresses by different processes.
102  * For null pointers, a value of 1 is used. (0 is legitimate
103  * sometimes for nodes in circularly linked lists) This value was
104  * chosen as the least likely to generate an incorrect null, As
105  * there is no reason why any normal pointer would point 1 byte into
106  * its own pointer address.
107  */
108  template<typename _Tp>
110  {
111  public:
112  typedef _Tp element_type;
113 
114  _Tp*
115  get() const
116  {
117  if (_M_diff == 1)
118  return 0;
119  else
120  return reinterpret_cast<_Tp*>(reinterpret_cast<_UIntPtrType>(this)
121  + _M_diff);
122  }
123 
124  void
125  set(_Tp* __arg)
126  {
127  if (!__arg)
128  _M_diff = 1;
129  else
130  _M_diff = reinterpret_cast<_UIntPtrType>(__arg)
131  - reinterpret_cast<_UIntPtrType>(this);
132  }
133 
134  // Comparison of pointers
135  inline bool
136  operator<(const _Relative_pointer_impl& __rarg) const
137  { return (reinterpret_cast<_UIntPtrType>(this->get())
138  < reinterpret_cast<_UIntPtrType>(__rarg.get())); }
139 
140  inline bool
141  operator==(const _Relative_pointer_impl& __rarg) const
142  { return (reinterpret_cast<_UIntPtrType>(this->get())
143  == reinterpret_cast<_UIntPtrType>(__rarg.get())); }
144 
145  private:
146 #ifdef _GLIBCXX_USE_LONG_LONG
147  typedef __gnu_cxx::__conditional_type<
148  (sizeof(unsigned long) >= sizeof(void*)),
149  unsigned long, unsigned long long>::__type _UIntPtrType;
150 #else
151  typedef unsigned long _UIntPtrType;
152 #endif
153  _UIntPtrType _M_diff;
154  };
155 
156  /**
157  * Relative_pointer_impl needs a specialization for const T because of
158  * the casting done during pointer arithmetic.
159  */
160  template<typename _Tp>
161  class _Relative_pointer_impl<const _Tp>
162  {
163  public:
164  typedef const _Tp element_type;
165 
166  const _Tp*
167  get() const
168  {
169  if (_M_diff == 1)
170  return 0;
171  else
172  return reinterpret_cast<const _Tp*>
173  (reinterpret_cast<_UIntPtrType>(this) + _M_diff);
174  }
175 
176  void
177  set(const _Tp* __arg)
178  {
179  if (!__arg)
180  _M_diff = 1;
181  else
182  _M_diff = reinterpret_cast<_UIntPtrType>(__arg)
183  - reinterpret_cast<_UIntPtrType>(this);
184  }
185 
186  // Comparison of pointers
187  inline bool
188  operator<(const _Relative_pointer_impl& __rarg) const
189  { return (reinterpret_cast<_UIntPtrType>(this->get())
190  < reinterpret_cast<_UIntPtrType>(__rarg.get())); }
191 
192  inline bool
193  operator==(const _Relative_pointer_impl& __rarg) const
194  { return (reinterpret_cast<_UIntPtrType>(this->get())
195  == reinterpret_cast<_UIntPtrType>(__rarg.get())); }
196 
197  private:
198 #ifdef _GLIBCXX_USE_LONG_LONG
199  typedef __gnu_cxx::__conditional_type<
200  (sizeof(unsigned long) >= sizeof(void*)),
201  unsigned long, unsigned long long>::__type _UIntPtrType;
202 #else
203  typedef unsigned long _UIntPtrType;
204 #endif
205  _UIntPtrType _M_diff;
206  };
207 
208  /**
209  * The specialization on this type helps resolve the problem of
210  * reference to void, and eliminates the need to specialize
211  * _Pointer_adapter for cases of void*, const void*, and so on.
212  */
213  struct _Invalid_type { };
214 
215  template<typename _Tp>
216  struct _Reference_type
217  { typedef _Tp& reference; };
218 
219  template<>
220  struct _Reference_type<void>
221  { typedef _Invalid_type& reference; };
222 
223  template<>
224  struct _Reference_type<const void>
225  { typedef const _Invalid_type& reference; };
226 
227  template<>
228  struct _Reference_type<volatile void>
229  { typedef volatile _Invalid_type& reference; };
230 
231  template<>
232  struct _Reference_type<volatile const void>
233  { typedef const volatile _Invalid_type& reference; };
234 
235  /**
236  * This structure accommodates the way in which
237  * std::iterator_traits<> is normally specialized for const T*, so
238  * that value_type is still T.
239  */
240  template<typename _Tp>
242  { typedef _Tp type; };
243 
244  template<typename _Tp>
245  struct _Unqualified_type<const _Tp>
246  { typedef _Tp type; };
247 
248  /**
249  * The following provides an 'alternative pointer' that works with
250  * the containers when specified as the pointer typedef of the
251  * allocator.
252  *
253  * The pointer type used with the containers doesn't have to be this
254  * class, but it must support the implicit conversions, pointer
255  * arithmetic, comparison operators, etc. that are supported by this
256  * class, and avoid raising compile-time ambiguities. Because
257  * creating a working pointer can be challenging, this pointer
258  * template was designed to wrapper an easier storage policy type,
259  * so that it becomes reusable for creating other pointer types.
260  *
261  * A key point of this class is also that it allows container
262  * writers to 'assume' Allocator::pointer is a typedef for a normal
263  * pointer. This class supports most of the conventions of a true
264  * pointer, and can, for instance handle implicit conversion to
265  * const and base class pointer types. The only impositions on
266  * container writers to support extended pointers are: 1) use the
267  * Allocator::pointer typedef appropriately for pointer types. 2)
268  * if you need pointer casting, use the __pointer_cast<> functions
269  * from ext/cast.h. This allows pointer cast operations to be
270  * overloaded as necessary by custom pointers.
271  *
272  * Note: The const qualifier works with this pointer adapter as
273  * follows:
274  *
275  * _Tp* == _Pointer_adapter<_Std_pointer_impl<_Tp> >;
276  * const _Tp* == _Pointer_adapter<_Std_pointer_impl<const _Tp> >;
277  * _Tp* const == const _Pointer_adapter<_Std_pointer_impl<_Tp> >;
278  * const _Tp* const == const _Pointer_adapter<_Std_pointer_impl<const _Tp> >;
279  */
280  template<typename _Storage_policy>
281  class _Pointer_adapter : public _Storage_policy
282  {
283  public:
284  typedef typename _Storage_policy::element_type element_type;
285 
286  // These are needed for iterator_traits
288  typedef typename _Unqualified_type<element_type>::type value_type;
289  typedef std::ptrdiff_t difference_type;
290  typedef _Pointer_adapter pointer;
291  typedef typename _Reference_type<element_type>::reference reference;
292 
293  // Reminder: 'const' methods mean that the method is valid when the
294  // pointer is immutable, and has nothing to do with whether the
295  // 'pointee' is const.
296 
297  // Default Constructor (Convert from element_type*)
298  _Pointer_adapter(element_type* __arg = 0)
299  { _Storage_policy::set(__arg); }
300 
301  // Copy constructor from _Pointer_adapter of same type.
302  _Pointer_adapter(const _Pointer_adapter& __arg)
303  { _Storage_policy::set(__arg.get()); }
304 
305  // Convert from _Up* if conversion to element_type* is valid.
306  template<typename _Up>
307  _Pointer_adapter(_Up* __arg)
308  { _Storage_policy::set(__arg); }
309 
310  // Conversion from another _Pointer_adapter if _Up if static cast is
311  // valid.
312  template<typename _Up>
314  { _Storage_policy::set(__arg.get()); }
315 
316  // Destructor
317  ~_Pointer_adapter() { }
318 
319  // Assignment operator
321  operator=(const _Pointer_adapter& __arg)
322  {
323  _Storage_policy::set(__arg.get());
324  return *this;
325  }
326 
327  template<typename _Up>
329  operator=(const _Pointer_adapter<_Up>& __arg)
330  {
331  _Storage_policy::set(__arg.get());
332  return *this;
333  }
334 
335  template<typename _Up>
337  operator=(_Up* __arg)
338  {
339  _Storage_policy::set(__arg);
340  return *this;
341  }
342 
343  // Operator*, returns element_type&
344  inline reference
345  operator*() const
346  { return *(_Storage_policy::get()); }
347 
348  // Operator->, returns element_type*
349  inline element_type*
350  operator->() const
351  { return _Storage_policy::get(); }
352 
353  // Operator[], returns a element_type& to the item at that loc.
354  inline reference
355  operator[](std::ptrdiff_t __index) const
356  { return _Storage_policy::get()[__index]; }
357 
358  // To allow implicit conversion to "bool", for "if (ptr)..."
359  private:
360  typedef element_type*(_Pointer_adapter::*__unspecified_bool_type)() const;
361 
362  public:
363  operator __unspecified_bool_type() const
364  {
365  return _Storage_policy::get() == 0 ? 0 :
366  &_Pointer_adapter::operator->;
367  }
368 
369  // ! operator (for: if (!ptr)...)
370  inline bool
371  operator!() const
372  { return (_Storage_policy::get() == 0); }
373 
374  // Pointer differences
375  inline friend std::ptrdiff_t
376  operator-(const _Pointer_adapter& __lhs, element_type* __rhs)
377  { return (__lhs.get() - __rhs); }
378 
379  inline friend std::ptrdiff_t
380  operator-(element_type* __lhs, const _Pointer_adapter& __rhs)
381  { return (__lhs - __rhs.get()); }
382 
383  template<typename _Up>
384  inline friend std::ptrdiff_t
385  operator-(const _Pointer_adapter& __lhs, _Up* __rhs)
386  { return (__lhs.get() - __rhs); }
387 
388  template<typename _Up>
389  inline friend std::ptrdiff_t
390  operator-(_Up* __lhs, const _Pointer_adapter& __rhs)
391  { return (__lhs - __rhs.get()); }
392 
393  template<typename _Up>
394  inline std::ptrdiff_t
395  operator-(const _Pointer_adapter<_Up>& __rhs) const
396  { return (_Storage_policy::get() - __rhs.get()); }
397 
398  // Pointer math
399  // Note: There is a reason for all this overloading based on different
400  // integer types. In some libstdc++-v3 test cases, a templated
401  // operator+ is declared which can match any types. This operator
402  // tends to "steal" the recognition of _Pointer_adapter's own operator+
403  // unless the integer type matches perfectly.
404 
405 #define _CXX_POINTER_ARITH_OPERATOR_SET(INT_TYPE) \
406  inline friend _Pointer_adapter \
407  operator+(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
408  { return _Pointer_adapter(__lhs.get() + __offset); } \
409 \
410  inline friend _Pointer_adapter \
411  operator+(INT_TYPE __offset, const _Pointer_adapter& __rhs) \
412  { return _Pointer_adapter(__rhs.get() + __offset); } \
413 \
414  inline friend _Pointer_adapter \
415  operator-(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
416  { return _Pointer_adapter(__lhs.get() - __offset); } \
417 \
418  inline _Pointer_adapter& \
419  operator+=(INT_TYPE __offset) \
420  { \
421  _Storage_policy::set(_Storage_policy::get() + __offset); \
422  return *this; \
423  } \
424 \
425  inline _Pointer_adapter& \
426  operator-=(INT_TYPE __offset) \
427  { \
428  _Storage_policy::set(_Storage_policy::get() - __offset); \
429  return *this; \
430  } \
431 // END of _CXX_POINTER_ARITH_OPERATOR_SET macro
432 
433  // Expand into the various pointer arithmetic operators needed.
434  _CXX_POINTER_ARITH_OPERATOR_SET(short);
435  _CXX_POINTER_ARITH_OPERATOR_SET(unsigned short);
436  _CXX_POINTER_ARITH_OPERATOR_SET(int);
437  _CXX_POINTER_ARITH_OPERATOR_SET(unsigned int);
438  _CXX_POINTER_ARITH_OPERATOR_SET(long);
439  _CXX_POINTER_ARITH_OPERATOR_SET(unsigned long);
440 #ifdef _GLIBCXX_USE_LONG_LONG
441  _CXX_POINTER_ARITH_OPERATOR_SET(long long);
442  _CXX_POINTER_ARITH_OPERATOR_SET(unsigned long long);
443 #endif
444 
445  // Mathematical Manipulators
446  inline _Pointer_adapter&
447  operator++()
448  {
449  _Storage_policy::set(_Storage_policy::get() + 1);
450  return *this;
451  }
452 
453  inline _Pointer_adapter
454  operator++(int)
455  {
456  _Pointer_adapter __tmp(*this);
457  _Storage_policy::set(_Storage_policy::get() + 1);
458  return __tmp;
459  }
460 
461  inline _Pointer_adapter&
462  operator--()
463  {
464  _Storage_policy::set(_Storage_policy::get() - 1);
465  return *this;
466  }
467 
468  inline _Pointer_adapter
469  operator--(int)
470  {
471  _Pointer_adapter __tmp(*this);
472  _Storage_policy::set(_Storage_policy::get() - 1);
473  return __tmp;
474  }
475 
476  }; // class _Pointer_adapter
477 
478 
479 #define _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(OPERATOR) \
480  template<typename _Tp1, typename _Tp2> \
481  inline bool \
482  operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, _Tp2 __rhs) \
483  { return __lhs.get() OPERATOR __rhs; } \
484 \
485  template<typename _Tp1, typename _Tp2> \
486  inline bool \
487  operator OPERATOR(_Tp1 __lhs, const _Pointer_adapter<_Tp2>& __rhs) \
488  { return __lhs OPERATOR __rhs.get(); } \
489 \
490  template<typename _Tp1, typename _Tp2> \
491  inline bool \
492  operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, \
493  const _Pointer_adapter<_Tp2>& __rhs) \
494  { return __lhs.get() OPERATOR __rhs.get(); } \
495 \
496 // End GCC_CXX_POINTER_COMPARISON_OPERATION_SET Macro
497 
498  // Expand into the various comparison operators needed.
499  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(==)
500  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(!=)
501  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(<)
502  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(<=)
503  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(>)
504  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(>=)
505 
506  // These are here for expressions like "ptr == 0", "ptr != 0"
507  template<typename _Tp>
508  inline bool
509  operator==(const _Pointer_adapter<_Tp>& __lhs, int __rhs)
510  { return __lhs.get() == reinterpret_cast<void*>(__rhs); }
511 
512  template<typename _Tp>
513  inline bool
514  operator==(int __lhs, const _Pointer_adapter<_Tp>& __rhs)
515  { return __rhs.get() == reinterpret_cast<void*>(__lhs); }
516 
517  template<typename _Tp>
518  inline bool
519  operator!=(const _Pointer_adapter<_Tp>& __lhs, int __rhs)
520  { return __lhs.get() != reinterpret_cast<void*>(__rhs); }
521 
522  template<typename _Tp>
523  inline bool
524  operator!=(int __lhs, const _Pointer_adapter<_Tp>& __rhs)
525  { return __rhs.get() != reinterpret_cast<void*>(__lhs); }
526 
527  /**
528  * Comparison operators for _Pointer_adapter defer to the base class'
529  * comparison operators, when possible.
530  */
531  template<typename _Tp>
532  inline bool
533  operator==(const _Pointer_adapter<_Tp>& __lhs,
534  const _Pointer_adapter<_Tp>& __rhs)
535  { return __lhs._Tp::operator==(__rhs); }
536 
537  template<typename _Tp>
538  inline bool
539  operator<=(const _Pointer_adapter<_Tp>& __lhs,
540  const _Pointer_adapter<_Tp>& __rhs)
541  { return __lhs._Tp::operator<(__rhs) || __lhs._Tp::operator==(__rhs); }
542 
543  template<typename _Tp>
544  inline bool
545  operator!=(const _Pointer_adapter<_Tp>& __lhs,
546  const _Pointer_adapter<_Tp>& __rhs)
547  { return !(__lhs._Tp::operator==(__rhs)); }
548 
549  template<typename _Tp>
550  inline bool
551  operator>(const _Pointer_adapter<_Tp>& __lhs,
552  const _Pointer_adapter<_Tp>& __rhs)
553  { return !(__lhs._Tp::operator<(__rhs) || __lhs._Tp::operator==(__rhs)); }
554 
555  template<typename _Tp>
556  inline bool
557  operator>=(const _Pointer_adapter<_Tp>& __lhs,
558  const _Pointer_adapter<_Tp>& __rhs)
559  { return !(__lhs._Tp::operator<(__rhs)); }
560 
561  template<typename _CharT, typename _Traits, typename _StoreT>
564  const _Pointer_adapter<_StoreT>& __p)
565  { return (__os << __p.get()); }
566 
567 _GLIBCXX_END_NAMESPACE_VERSION
568 } // namespace
569 
570 #if __cplusplus >= 201103L
571 namespace std _GLIBCXX_VISIBILITY(default)
572 {
573 _GLIBCXX_BEGIN_NAMESPACE_VERSION
574 
575  template<typename _Storage_policy>
576  struct pointer_traits<__gnu_cxx::_Pointer_adapter<_Storage_policy>>
577  {
578  /// The pointer type
580  /// The type pointed to
581  typedef typename pointer::element_type element_type;
582  /// Type used to represent the difference between two pointers
583  typedef typename pointer::difference_type difference_type;
584 
585  template<typename _Up>
586  using rebind = typename __gnu_cxx::_Pointer_adapter<
587  typename pointer_traits<_Storage_policy>::template rebind<_Up>>;
588 
589  static pointer pointer_to(typename pointer::reference __r) noexcept
590  { return pointer(std::addressof(__r)); }
591  };
592 
593 _GLIBCXX_END_NAMESPACE_VERSION
594 } // namespace
595 #endif
596 
597 #endif // _POINTER_H
A storage policy for use with _Pointer_adapter<> which yields a standard pointer.
Definition: pointer.h:66
__detected_or_t< ptrdiff_t, __difference_type, _Ptr > difference_type
The type used to represent the difference between two pointers.
Definition: ptr_traits.h:104
GNU extensions for public use.
_GLIBCXX17_CONSTEXPR _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:138
ISO C++ entities toplevel namespace is std.
__detected_or_t< __get_first_arg_t< _Ptr >, __element_type, _Ptr > element_type
The type pointed to.
Definition: ptr_traits.h:100
Template class basic_ostream.
Definition: iosfwd:86
std::basic_ostream< _CharT, _Traits > & operator<<(std::basic_ostream< _CharT, _Traits > &__os, const bitset< _Nb > &__x)
Global I/O operators for bitsets.
Definition: bitset:1534
typename __rebind< _Ptr, _Up >::type rebind
A pointer to a different type.
Definition: ptr_traits.h:108
Random-access iterators support a superset of bidirectional iterator operations.
A storage policy for use with _Pointer_adapter<> which stores the pointer's address as an offset valu...
Definition: pointer.h:109
_Ptr pointer
The pointer type.
Definition: ptr_traits.h:96