libstdc++-v3/include/ext/pointer.h

   1 // Custom pointer adapter and sample storage policies
   2
   3 // Copyright (C) 2008-2019 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>
  42 #include <bits/stl_iterator_base_types.h>
  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>
  66     class _Std_pointer_impl
  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>
 109     class _Relative_pointer_impl
 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>
 241     struct _Unqualified_type
 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
 287       typedef std::random_access_iterator_tag                iterator_category;
 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>
 313         _Pointer_adapter(const _Pointer_adapter<_Up>& __arg)
 314         { _Storage_policy::set(__arg.get()); }
 315
 316       // Destructor
 317       ~_Pointer_adapter() { }
 318
 319       // Assignment operator
 320       _Pointer_adapter&
 321       operator=(const _Pointer_adapter& __arg)
 322       {
 323         _Storage_policy::set(__arg.get());
 324         return *this;
 325       }
 326
 327       template<typename _Up>
 328         _Pointer_adapter&
 329         operator=(const _Pointer_adapter<_Up>& __arg)
 330         {
 331           _Storage_policy::set(__arg.get());
 332           return *this;
 333         }
 334
 335       template<typename _Up>
 336         _Pointer_adapter&
 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 #if __cplusplus >= 201103L
 360       explicit operator bool() const { return _Storage_policy::get() != 0; }
 361 #else
 362     private:
 363       typedef element_type*(_Pointer_adapter::*__unspecified_bool_type)() const;
 364
 365     public:
 366       operator __unspecified_bool_type() const
 367       {
 368         return _Storage_policy::get() == 0 ? 0 :
 369                          &_Pointer_adapter::operator->;
 370       }
 371
 372       // ! operator (for: if (!ptr)...)
 373       inline bool
 374       operator!() const
 375       { return (_Storage_policy::get() == 0); }
 376 #endif
 377
 378       // Pointer differences
 379       inline friend std::ptrdiff_t
 380       operator-(const _Pointer_adapter& __lhs, element_type* __rhs)
 381       { return (__lhs.get() - __rhs); }
 382
 383       inline friend std::ptrdiff_t
 384       operator-(element_type* __lhs, const _Pointer_adapter& __rhs)
 385       { return (__lhs - __rhs.get()); }
 386
 387       template<typename _Up>
 388         inline friend std::ptrdiff_t
 389         operator-(const _Pointer_adapter& __lhs, _Up* __rhs)
 390         { return (__lhs.get() - __rhs); }
 391
 392       template<typename _Up>
 393         inline friend std::ptrdiff_t
 394         operator-(_Up* __lhs, const _Pointer_adapter& __rhs)
 395         { return (__lhs - __rhs.get()); }
 396
 397       template<typename _Up>
 398         inline std::ptrdiff_t
 399         operator-(const _Pointer_adapter<_Up>& __rhs) const
 400         { return (_Storage_policy::get() - __rhs.get()); }
 401
 402       // Pointer math
 403       // Note: There is a reason for all this overloading based on different
 404       // integer types.  In some libstdc++-v3 test cases, a templated
 405       // operator+ is declared which can match any types.  This operator
 406       // tends to "steal" the recognition of _Pointer_adapter's own operator+
 407       // unless the integer type matches perfectly.
 408
 409 #define _CXX_POINTER_ARITH_OPERATOR_SET(INT_TYPE) \
 410       inline friend _Pointer_adapter \
 411       operator+(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
 412       { return _Pointer_adapter(__lhs.get() + __offset); } \
 413 \
 414       inline friend _Pointer_adapter \
 415       operator+(INT_TYPE __offset, const _Pointer_adapter& __rhs) \
 416       { return _Pointer_adapter(__rhs.get() + __offset); } \
 417 \
 418       inline friend _Pointer_adapter \
 419       operator-(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
 420       { return _Pointer_adapter(__lhs.get() - __offset); } \
 421 \
 422       inline _Pointer_adapter& \
 423       operator+=(INT_TYPE __offset) \
 424       { \
 425         _Storage_policy::set(_Storage_policy::get() + __offset); \
 426         return *this; \
 427       } \
 428 \
 429       inline _Pointer_adapter& \
 430       operator-=(INT_TYPE __offset) \
 431       { \
 432         _Storage_policy::set(_Storage_policy::get() - __offset); \
 433         return *this; \
 434       } \
 435 // END of _CXX_POINTER_ARITH_OPERATOR_SET macro
 436
 437       // Expand into the various pointer arithmetic operators needed.
 438       _CXX_POINTER_ARITH_OPERATOR_SET(short);
 439       _CXX_POINTER_ARITH_OPERATOR_SET(unsigned short);
 440       _CXX_POINTER_ARITH_OPERATOR_SET(int);
 441       _CXX_POINTER_ARITH_OPERATOR_SET(unsigned int);
 442       _CXX_POINTER_ARITH_OPERATOR_SET(long);
 443       _CXX_POINTER_ARITH_OPERATOR_SET(unsigned long);
 444 #ifdef _GLIBCXX_USE_LONG_LONG
 445       _CXX_POINTER_ARITH_OPERATOR_SET(long long);
 446       _CXX_POINTER_ARITH_OPERATOR_SET(unsigned long long);
 447 #endif
 448
 449       // Mathematical Manipulators
 450       inline _Pointer_adapter&
 451       operator++()
 452       {
 453         _Storage_policy::set(_Storage_policy::get() + 1);
 454         return *this;
 455       }
 456
 457       inline _Pointer_adapter
 458       operator++(int)
 459       {
 460         _Pointer_adapter __tmp(*this);
 461         _Storage_policy::set(_Storage_policy::get() + 1);
 462         return __tmp;
 463       }
 464
 465       inline _Pointer_adapter&
 466       operator--()
 467       {
 468         _Storage_policy::set(_Storage_policy::get() - 1);
 469         return *this;
 470       }
 471
 472       inline _Pointer_adapter
 473       operator--(int)
 474       {
 475         _Pointer_adapter __tmp(*this);
 476         _Storage_policy::set(_Storage_policy::get() - 1);
 477         return __tmp;
 478       }
 479
 480     }; // class _Pointer_adapter
 481
 482
 483 #define _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(OPERATOR) \
 484   template<typename _Tp1, typename _Tp2> \
 485     inline bool \
 486     operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, _Tp2 __rhs) \
 487     { return __lhs.get() OPERATOR __rhs; } \
 488 \
 489   template<typename _Tp1, typename _Tp2> \
 490     inline bool \
 491     operator OPERATOR(_Tp1 __lhs, const _Pointer_adapter<_Tp2>& __rhs) \
 492     { return __lhs OPERATOR __rhs.get(); } \
 493 \
 494   template<typename _Tp1, typename _Tp2> \
 495     inline bool \
 496     operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, \
 497                               const _Pointer_adapter<_Tp2>& __rhs) \
 498     { return __lhs.get() OPERATOR __rhs.get(); } \
 499 \
 500 // End GCC_CXX_POINTER_COMPARISON_OPERATION_SET Macro
 501
 502   // Expand into the various comparison operators needed.
 503   _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(==)
 504   _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(!=)
 505   _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(<)
 506   _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(<=)
 507   _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(>)
 508   _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(>=)
 509
 510   // These are here for expressions like "ptr == 0", "ptr != 0"
 511   template<typename _Tp>
 512     inline bool
 513     operator==(const _Pointer_adapter<_Tp>& __lhs, int __rhs)
 514     { return __lhs.get() == reinterpret_cast<void*>(__rhs); }
 515
 516   template<typename _Tp>
 517     inline bool
 518     operator==(int __lhs, const _Pointer_adapter<_Tp>& __rhs)
 519     { return __rhs.get() == reinterpret_cast<void*>(__lhs); }
 520
 521   template<typename _Tp>
 522     inline bool
 523     operator!=(const _Pointer_adapter<_Tp>& __lhs, int __rhs)
 524     { return __lhs.get() != reinterpret_cast<void*>(__rhs); }
 525
 526   template<typename _Tp>
 527     inline bool
 528     operator!=(int __lhs, const _Pointer_adapter<_Tp>& __rhs)
 529     { return __rhs.get() != reinterpret_cast<void*>(__lhs); }
 530
 531   /**
 532    * Comparison operators for _Pointer_adapter defer to the base class'
 533    * comparison operators, when possible.
 534    */
 535   template<typename _Tp>
 536     inline bool
 537     operator==(const _Pointer_adapter<_Tp>& __lhs,
 538                const _Pointer_adapter<_Tp>& __rhs)
 539     { return __lhs._Tp::operator==(__rhs); }
 540
 541   template<typename _Tp>
 542     inline bool
 543     operator<=(const _Pointer_adapter<_Tp>& __lhs,
 544                const _Pointer_adapter<_Tp>& __rhs)
 545     { return __lhs._Tp::operator<(__rhs) || __lhs._Tp::operator==(__rhs); }
 546
 547   template<typename _Tp>
 548     inline bool
 549     operator!=(const _Pointer_adapter<_Tp>& __lhs,
 550                const _Pointer_adapter<_Tp>& __rhs)
 551     { return !(__lhs._Tp::operator==(__rhs)); }
 552
 553   template<typename _Tp>
 554     inline bool
 555     operator>(const _Pointer_adapter<_Tp>& __lhs,
 556               const _Pointer_adapter<_Tp>& __rhs)
 557     { return !(__lhs._Tp::operator<(__rhs) || __lhs._Tp::operator==(__rhs)); }
 558
 559   template<typename _Tp>
 560     inline bool
 561     operator>=(const _Pointer_adapter<_Tp>& __lhs,
 562                const _Pointer_adapter<_Tp>& __rhs)
 563     { return !(__lhs._Tp::operator<(__rhs)); }
 564
 565   template<typename _CharT, typename _Traits, typename _StoreT>
 566     inline std::basic_ostream<_CharT, _Traits>&
 567     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
 568                const _Pointer_adapter<_StoreT>& __p)
 569     { return (__os << __p.get()); }
 570
 571 _GLIBCXX_END_NAMESPACE_VERSION
 572 } // namespace
 573
 574 #if __cplusplus >= 201103L
 575 namespace std _GLIBCXX_VISIBILITY(default)
 576 {
 577 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 578
 579   template<typename _Storage_policy>
 580     struct pointer_traits<__gnu_cxx::_Pointer_adapter<_Storage_policy>>
 581     {
 582       /// The pointer type
 583       typedef __gnu_cxx::_Pointer_adapter<_Storage_policy>         pointer;
 584       /// The type pointed to
 585       typedef typename pointer::element_type            element_type;
 586       /// Type used to represent the difference between two pointers
 587       typedef typename pointer::difference_type         difference_type;
 588
 589       template<typename _Up>
 590         using rebind = typename __gnu_cxx::_Pointer_adapter<
 591         typename pointer_traits<_Storage_policy>::template rebind<_Up>>;
 592
 593       static pointer pointer_to(typename pointer::reference __r) noexcept
 594       { return pointer(std::addressof(__r)); }
 595     };
 596
 597 _GLIBCXX_END_NAMESPACE_VERSION
 598 } // namespace
 599 #endif
 600
 601 #endif // _POINTER_H