pointer.h File Reference

#include <iosfwd>
#include <bits/stl_iterator_base_types.h>
#include <ext/cast.h>
#include <ext/type_traits.h>

Go to the source code of this file.

Macros
#define	_CXX_POINTER_ARITH_OPERATOR_SET(INT_TYPE)
#define	_GCC_CXX_POINTER_COMPARISON_OPERATION_SET(OPERATOR)

Functions
namespace __gnu_cxx	_GLIBCXX_VISIBILITY (default)

Detailed Description

This file is a GNU extension to the Standard C++ Library.

Author

Bob Walters

Provides reusable _Pointer_adapter for assisting in the development of custom pointer types that can be used with the standard containers via the allocator::pointer and allocator::const_pointer typedefs.

Macro Definition Documentation

#define _CXX_POINTER_ARITH_OPERATOR_SET

(

INT_TYPE

)

Value:

inline friend _Pointer_adapter \
      operator+(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
      { return _Pointer_adapter(__lhs.get() + __offset); } \
\
      inline friend _Pointer_adapter \
      operator+(INT_TYPE __offset, const _Pointer_adapter& __rhs) \
      { return _Pointer_adapter(__rhs.get() + __offset); } \
\
      inline friend _Pointer_adapter \
      operator-(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
      { return _Pointer_adapter(__lhs.get() - __offset); } \
\
      inline _Pointer_adapter& \
      operator+=(INT_TYPE __offset) \
      { \
        _Storage_policy::set(_Storage_policy::get() + __offset); \
        return *this; \
      } \
\
      inline _Pointer_adapter& \
      operator-=(INT_TYPE __offset) \
      { \
        _Storage_policy::set(_Storage_policy::get() - __offset); \
        return *this; \
      } \

#define _GCC_CXX_POINTER_COMPARISON_OPERATION_SET

(

OPERATOR

)

Value:

template<typename _Tp1, typename _Tp2> \
    inline bool \
    operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, _Tp2 __rhs) \
    { return __lhs.get() OPERATOR __rhs; } \
\
  template<typename _Tp1, typename _Tp2> \
    inline bool \
    operator OPERATOR(_Tp1 __lhs, const _Pointer_adapter<_Tp2>& __rhs) \
    { return __lhs OPERATOR __rhs.get(); } \
\
  template<typename _Tp1, typename _Tp2> \
    inline bool \
    operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, \
                              const _Pointer_adapter<_Tp2>& __rhs) \
    { return __lhs.get() OPERATOR __rhs.get(); } \
\

Function Documentation

namespace __gnu_cxx _GLIBCXX_VISIBILITY

(

default

)

A storage policy for use with _Pointer_adapter<> which yields a standard pointer.

A _Storage_policy is required to provide 4 things: 1) A get() API for returning the stored pointer value. 2) An set() API for storing a pointer value. 3) An element_type typedef to define the type this points to. 4) An operator<() to support pointer comparison. 5) An operator==() to support pointer comparison.

A storage policy for use with _Pointer_adapter<> which stores the pointer's address as an offset value which is relative to its own address.

This is intended for pointers within shared memory regions which might be mapped at different addresses by different processes. For null pointers, a value of 1 is used. (0 is legitimate sometimes for nodes in circularly linked lists) This value was chosen as the least likely to generate an incorrect null, As there is no reason why any normal pointer would point 1 byte into its own pointer address.

Relative_pointer_impl needs a specialization for const T because of the casting done during pointer arithmetic.

The specialization on this type helps resolve the problem of reference to void, and eliminates the need to specialize _Pointer_adapter for cases of void*, const void*, and so on.

This structure accommodates the way in which std::iterator_traits<> is normally specialized for const T*, so that value_type is still T.

The following provides an 'alternative pointer' that works with the containers when specified as the pointer typedef of the allocator.

The pointer type used with the containers doesn't have to be this class, but it must support the implicit conversions, pointer arithmetic, comparison operators, etc. that are supported by this class, and avoid raising compile-time ambiguities. Because creating a working pointer can be challenging, this pointer template was designed to wrapper an easier storage policy type, so that it becomes reusable for creating other pointer types.

A key point of this class is also that it allows container writers to 'assume' Allocator::pointer is a typedef for a normal pointer. This class supports most of the conventions of a true pointer, and can, for instance handle implicit conversion to const and base class pointer types. The only impositions on container writers to support extended pointers are: 1) use the Allocator::pointer typedef appropriately for pointer types. 2) if you need pointer casting, use the __pointer_cast<> functions from ext/cast.h. This allows pointer cast operations to be overloaded as necessary by custom pointers.

Note: The const qualifier works with this pointer adapter as follows:

_Tp* == _Pointer_adapter<_Std_pointer_impl<_Tp> >; const _Tp* == _Pointer_adapter<_Std_pointer_impl<const _Tp> >; _Tp* const == const _Pointer_adapter<_Std_pointer_impl<_Tp> >; const _Tp* const == const _Pointer_adapter<_Std_pointer_impl<const _Tp> >;

Comparison operators for _Pointer_adapter defer to the base class' comparison operators, when possible.

{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  template<typename _Tp> 
    class _Std_pointer_impl 
    {
    public:
      // the type this pointer points to.
      typedef _Tp element_type;
  
      // A method to fetch the pointer value as a standard T* value;
      inline _Tp* 
      get() const 
      { return _M_value; }
  
      // A method to set the pointer value, from a standard T* value;
      inline void 
      set(element_type* __arg) 
      { _M_value = __arg; }
  
      // Comparison of pointers
      inline bool
      operator<(const _Std_pointer_impl& __rarg) const
      { return (_M_value < __rarg._M_value); }
  
      inline bool
      operator==(const _Std_pointer_impl& __rarg) const
      { return (_M_value == __rarg._M_value); }

    private:
      element_type* _M_value;
    };

  template<typename _Tp> 
    class _Relative_pointer_impl 
    {
    public:
      typedef _Tp element_type;
  
      _Tp*
      get() const 
      {
        if (_M_diff == 1)
          return 0;
        else
          return reinterpret_cast<_Tp*>(reinterpret_cast<_UIntPtrType>(this)
                    + _M_diff);
      }
  
      void 
      set(_Tp* __arg)
      {
        if (!__arg)
          _M_diff = 1;
        else
          _M_diff = reinterpret_cast<_UIntPtrType>(__arg) 
                    - reinterpret_cast<_UIntPtrType>(this);
      }
  
      // Comparison of pointers
      inline bool
      operator<(const _Relative_pointer_impl& __rarg) const
      { return (reinterpret_cast<_UIntPtrType>(this->get())
        < reinterpret_cast<_UIntPtrType>(__rarg.get())); }

      inline bool
      operator==(const _Relative_pointer_impl& __rarg) const
      { return (reinterpret_cast<_UIntPtrType>(this->get())
        == reinterpret_cast<_UIntPtrType>(__rarg.get())); }

    private:
#ifdef _GLIBCXX_USE_LONG_LONG
      typedef __gnu_cxx::__conditional_type<
     (sizeof(unsigned long) >= sizeof(void*)),
     unsigned long, unsigned long long>::__type _UIntPtrType;
#else
      typedef unsigned long _UIntPtrType;
#endif
      _UIntPtrType _M_diff;
    };
  
  template<typename _Tp> 
    class _Relative_pointer_impl<const _Tp> 
    {
    public:
      typedef const _Tp element_type;
  
      const _Tp*
      get() const
      {
        if (_M_diff == 1)
          return 0;
        else
          return reinterpret_cast<const _Tp*>
          (reinterpret_cast<_UIntPtrType>(this) + _M_diff);
      }
  
      void 
      set(const _Tp* __arg)
      {
        if (!__arg)
          _M_diff = 1;
        else
          _M_diff = reinterpret_cast<_UIntPtrType>(__arg) 
                    - reinterpret_cast<_UIntPtrType>(this);
      }
  
      // Comparison of pointers
      inline bool
      operator<(const _Relative_pointer_impl& __rarg) const
      { return (reinterpret_cast<_UIntPtrType>(this->get())
        < reinterpret_cast<_UIntPtrType>(__rarg.get())); }

      inline bool
      operator==(const _Relative_pointer_impl& __rarg) const
      { return (reinterpret_cast<_UIntPtrType>(this->get())
        == reinterpret_cast<_UIntPtrType>(__rarg.get())); }
  
    private:
#ifdef _GLIBCXX_USE_LONG_LONG
      typedef __gnu_cxx::__conditional_type<
     (sizeof(unsigned long) >= sizeof(void*)),
     unsigned long, unsigned long long>::__type _UIntPtrType;
#else
      typedef unsigned long _UIntPtrType;
#endif
       _UIntPtrType _M_diff;
    };

  struct _Invalid_type { };
  
  template<typename _Tp>
    struct _Reference_type 
    { typedef _Tp& reference; };

  template<> 
    struct _Reference_type<void> 
    { typedef _Invalid_type& reference; };

  template<> 
    struct _Reference_type<const void> 
    { typedef const _Invalid_type& reference; };

  template<> 
    struct _Reference_type<volatile void> 
    { typedef volatile _Invalid_type&  reference; };

  template<> 
    struct _Reference_type<volatile const void> 
    { typedef const volatile _Invalid_type&  reference; };

  template<typename _Tp> 
    struct _Unqualified_type 
    { typedef _Tp type; };
    
  template<typename _Tp> 
    struct _Unqualified_type<const _Tp> 
    { typedef _Tp type; };
    
  template<typename _Storage_policy>
    class _Pointer_adapter : public _Storage_policy 
    {
    public:
      typedef typename _Storage_policy::element_type element_type;

      // These are needed for iterator_traits
      typedef std::random_access_iterator_tag                iterator_category;
      typedef typename _Unqualified_type<element_type>::type value_type;
      typedef std::ptrdiff_t                                 difference_type;
      typedef _Pointer_adapter                               pointer;
      typedef typename _Reference_type<element_type>::reference  reference;

      // Reminder: 'const' methods mean that the method is valid when the 
      // pointer is immutable, and has nothing to do with whether the 
      // 'pointee' is const.

      // Default Constructor (Convert from element_type*)
      _Pointer_adapter(element_type* __arg = 0)
      { _Storage_policy::set(__arg); }

      // Copy constructor from _Pointer_adapter of same type.
      _Pointer_adapter(const _Pointer_adapter& __arg) 
      { _Storage_policy::set(__arg.get()); }

      // Convert from _Up* if conversion to element_type* is valid.
      template<typename _Up>
        _Pointer_adapter(_Up* __arg)
        { _Storage_policy::set(__arg); }

      // Conversion from another _Pointer_adapter if _Up if static cast is
      // valid.
      template<typename _Up>
        _Pointer_adapter(const _Pointer_adapter<_Up>& __arg)
        { _Storage_policy::set(__arg.get()); }

      // Destructor
      ~_Pointer_adapter() { }
  
      // Assignment operator
      _Pointer_adapter&
      operator=(const _Pointer_adapter& __arg) 
      {
        _Storage_policy::set(__arg.get()); 
        return *this; 
      }

      template<typename _Up>
        _Pointer_adapter&
        operator=(const _Pointer_adapter<_Up>& __arg)
        {
          _Storage_policy::set(__arg.get()); 
          return *this; 
        }

      template<typename _Up>
        _Pointer_adapter&
        operator=(_Up* __arg)
        {
          _Storage_policy::set(__arg); 
          return *this; 
        }

      // Operator*, returns element_type&
      inline reference 
      operator*() const 
      { return *(_Storage_policy::get()); }

      // Operator->, returns element_type*
      inline element_type* 
      operator->() const 
      { return _Storage_policy::get(); }

      // Operator[], returns a element_type& to the item at that loc.
      inline reference
      operator[](std::ptrdiff_t __index) const
      { return _Storage_policy::get()[__index]; }

      // To allow implicit conversion to "bool", for "if (ptr)..."
    private:
      typedef element_type*(_Pointer_adapter::*__unspecified_bool_type)() const;

    public:
      operator __unspecified_bool_type() const
      {
        return _Storage_policy::get() == 0 ? 0 : 
                         &_Pointer_adapter::operator->; 
      }

      // ! operator (for: if (!ptr)...)
      inline bool
      operator!() const 
      { return (_Storage_policy::get() == 0); }
  
      // Pointer differences
      inline friend std::ptrdiff_t 
      operator-(const _Pointer_adapter& __lhs, element_type* __rhs) 
      { return (__lhs.get() - __rhs); }
  
      inline friend std::ptrdiff_t 
      operator-(element_type* __lhs, const _Pointer_adapter& __rhs) 
      { return (__lhs - __rhs.get()); }
  
      template<typename _Up>
        inline friend std::ptrdiff_t 
        operator-(const _Pointer_adapter& __lhs, _Up* __rhs) 
        { return (__lhs.get() - __rhs); }
    
      template<typename _Up>
        inline friend std::ptrdiff_t 
        operator-(_Up* __lhs, const _Pointer_adapter& __rhs)
        { return (__lhs - __rhs.get()); }

      template<typename _Up>
        inline std::ptrdiff_t 
        operator-(const _Pointer_adapter<_Up>& __rhs) const 
        { return (_Storage_policy::get() - __rhs.get()); }
  
      // Pointer math
      // Note: There is a reason for all this overloading based on different
      // integer types.  In some libstdc++-v3 test cases, a templated
      // operator+ is declared which can match any types.  This operator
      // tends to "steal" the recognition of _Pointer_adapter's own operator+ 
      // unless the integer type matches perfectly.

#define _CXX_POINTER_ARITH_OPERATOR_SET(INT_TYPE) \
      inline friend _Pointer_adapter \
      operator+(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
      { return _Pointer_adapter(__lhs.get() + __offset); } \
\
      inline friend _Pointer_adapter \
      operator+(INT_TYPE __offset, const _Pointer_adapter& __rhs) \
      { return _Pointer_adapter(__rhs.get() + __offset); } \
\
      inline friend _Pointer_adapter \
      operator-(const _Pointer_adapter& __lhs, INT_TYPE __offset) \
      { return _Pointer_adapter(__lhs.get() - __offset); } \
\
      inline _Pointer_adapter& \
      operator+=(INT_TYPE __offset) \
      { \
        _Storage_policy::set(_Storage_policy::get() + __offset); \
        return *this; \
      } \
\
      inline _Pointer_adapter& \
      operator-=(INT_TYPE __offset) \
      { \
        _Storage_policy::set(_Storage_policy::get() - __offset); \
        return *this; \
      } \
// END of _CXX_POINTER_ARITH_OPERATOR_SET macro
  
      // Expand into the various pointer arithmetic operators needed.
      _CXX_POINTER_ARITH_OPERATOR_SET(short);
      _CXX_POINTER_ARITH_OPERATOR_SET(unsigned short);
      _CXX_POINTER_ARITH_OPERATOR_SET(int);
      _CXX_POINTER_ARITH_OPERATOR_SET(unsigned int);
      _CXX_POINTER_ARITH_OPERATOR_SET(long);
      _CXX_POINTER_ARITH_OPERATOR_SET(unsigned long);

      // Mathematical Manipulators
      inline _Pointer_adapter& 
      operator++()
      {
        _Storage_policy::set(_Storage_policy::get() + 1); 
        return *this;
      }
  
      inline _Pointer_adapter 
      operator++(int)
      {
        _Pointer_adapter tmp(*this);
        _Storage_policy::set(_Storage_policy::get() + 1);
        return tmp;
      }
  
      inline _Pointer_adapter& 
      operator--() 
      {
        _Storage_policy::set(_Storage_policy::get() - 1); 
        return *this;
      }
  
      inline _Pointer_adapter
      operator--(int) 
      {
        _Pointer_adapter tmp(*this);
        _Storage_policy::set(_Storage_policy::get() - 1);
        return tmp;
      }
  
    }; // class _Pointer_adapter


#define _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(OPERATOR) \
  template<typename _Tp1, typename _Tp2> \
    inline bool \
    operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, _Tp2 __rhs) \
    { return __lhs.get() OPERATOR __rhs; } \
\
  template<typename _Tp1, typename _Tp2> \
    inline bool \
    operator OPERATOR(_Tp1 __lhs, const _Pointer_adapter<_Tp2>& __rhs) \
    { return __lhs OPERATOR __rhs.get(); } \
\
  template<typename _Tp1, typename _Tp2> \
    inline bool \
    operator OPERATOR(const _Pointer_adapter<_Tp1>& __lhs, \
                              const _Pointer_adapter<_Tp2>& __rhs) \
    { return __lhs.get() OPERATOR __rhs.get(); } \
\
// End GCC_CXX_POINTER_COMPARISON_OPERATION_SET Macro
  
  // Expand into the various comparison operators needed.
  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(==)
  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(!=)
  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(<)
  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(<=)
  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(>)
  _GCC_CXX_POINTER_COMPARISON_OPERATION_SET(>=)

  // These are here for expressions like "ptr == 0", "ptr != 0"
  template<typename _Tp>
    inline bool
    operator==(const _Pointer_adapter<_Tp>& __lhs, int __rhs)
    { return __lhs.get() == reinterpret_cast<void*>(__rhs); } 

  template<typename _Tp>
    inline bool
    operator==(int __lhs, const _Pointer_adapter<_Tp>& __rhs)
    { return __rhs.get() == reinterpret_cast<void*>(__lhs); } 

  template<typename _Tp>
    inline bool
    operator!=(const _Pointer_adapter<_Tp>& __lhs, int __rhs)
    { return __lhs.get() != reinterpret_cast<void*>(__rhs); } 

  template<typename _Tp>
    inline bool
    operator!=(int __lhs, const _Pointer_adapter<_Tp>& __rhs)
    { return __rhs.get() != reinterpret_cast<void*>(__lhs); } 

  template<typename _Tp>
    inline bool
    operator==(const _Pointer_adapter<_Tp>& __lhs, 
               const _Pointer_adapter<_Tp>& __rhs)
    { return __lhs._Tp::operator==(__rhs); }

  template<typename _Tp>
    inline bool
    operator<=(const _Pointer_adapter<_Tp>& __lhs, 
               const _Pointer_adapter<_Tp>& __rhs)
    { return __lhs._Tp::operator<(__rhs) || __lhs._Tp::operator==(__rhs); }

  template<typename _Tp>
    inline bool
    operator!=(const _Pointer_adapter<_Tp>& __lhs, 
               const _Pointer_adapter<_Tp>& __rhs)
    { return !(__lhs._Tp::operator==(__rhs)); }

  template<typename _Tp>
    inline bool
    operator>(const _Pointer_adapter<_Tp>& __lhs, 
              const _Pointer_adapter<_Tp>& __rhs)
    { return !(__lhs._Tp::operator<(__rhs) || __lhs._Tp::operator==(__rhs)); }

  template<typename _Tp>
    inline bool
    operator>=(const _Pointer_adapter<_Tp>& __lhs, 
               const _Pointer_adapter<_Tp>& __rhs)
    { return !(__lhs._Tp::operator<(__rhs)); }

  template<typename _CharT, typename _Traits, typename _StoreT>
    inline std::basic_ostream<_CharT, _Traits>&
    operator<<(std::basic_ostream<_CharT, _Traits>& __os, 
               const _Pointer_adapter<_StoreT>& __p)
    { return (__os << __p.get()); }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace