Как решить эту ошибку в хеш-функции unordered_set пользовательских объектов класса? - PullRequest
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Как решить эту ошибку в хеш-функции unordered_set пользовательских объектов класса?

0 голосов
/ 29 апреля 2018

Я впервые использую неупорядоченную карту с пользовательскими объектами. Я пытался написать следующие функции. Есть ошибки, с которыми мне нужна помощь.

Это класс. 

class Node
{
  public:
    int g= 0, h=0;
    char val;                                                              //Char value in the grid
    pair<int,int> pos,parent;  
    bool par_prsnt = false;                                                //Bool to check if the parent is set


    Node(pair<int,int>nodePos,char value)
    {
    pos=nodePos;
    val=value;
    }  

    int move_cost(Node other)
    {
    if (val=='.')
        return 0;
    else
        return 1;
    }

    pair<int,int> get_pos() const
    {
    return pos;
    }

    void set_parent(pair<int,int> par)
    {
    parent = par;
    par_prsnt = true;
    }

};

Ниже приведены пользовательские функции: 

// Custom Hasher for Class Node, to be used for Unordered_set
struct NodeHasher
{
  template <typename T, typename U>
  size_t
  const operator()(const Node &obj)
  {
    pair<T,U> position;
    position = obj.get_pos();
    return 3* std::hash<T>()(position.first) + std::hash<U>()(position.second) ;
  }
};

// Custom Comparator for Class Node, to be used for Unordered_set
struct NodeComparator
{
  bool
  const operator()(const Node  &obj1, const  Node  &obj2) const
  {
    if (obj1.get_pos() == obj2.get_pos())
      return true;
    return false;
  }
};

Я получаю следующие ошибки: 

Player 1: compilation error
In file included from /usr/include/c++/7/bits/hashtable.h:35:0,
from /usr/include/c++/7/unordered_map:47,
from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:117,
solution.cc:7:
/usr/include/c++/7/bits/hashtable_policy.h: In instantiation of ‘struct std::__detail::__is_noexcept_hash’:
/usr/include/c++/7/type_traits:143:12: required from ‘struct std::__and_,  std::__detail::__is_noexcept_hash >’
/usr/include/c++/7/type_traits:154:31: required from ‘struct std::__not_, std::__detail::__is_noexcept_hash > >’
/usr/include/c++/7/bits/unordered_set.h:98:63: required from ‘class std::unordered_set’
solution.cc:119:51: required from here
/usr/include/c++/7/bits/hashtable_policy.h:87:34: error: no match for call to ‘(const NodeHasher) (const Node&)’
noexcept(declval()(declval()))>
~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
solution.cc:83:9: note: candidate: template const size_t NodeHasher::operator()(const Node&)
const operator()(const Node &obj)
^~~~~~~~
solution.cc:83:9: note: template argument deduction/substitution failed:
In file included from /usr/include/c++/7/bits/hashtable.h:35:0,
from /usr/include/c++/7/unordered_map:47,
from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:117,
solution.cc:7:
/usr/include/c++/7/bits/hashtable_policy.h:87:34: note: couldn't deduce template parameter ‘T’
noexcept(declval()(declval()))>
~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/7/bits/move.h:54:0,
from /usr/include/c++/7/bits/stl_pair.h:59,
from /usr/include/c++/7/bits/stl_algobase.h:64,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/type_traits: In instantiation of ‘struct std::__not_, std::__detail::__is_noexcept_hash > >’:
/usr/include/c++/7/bits/unordered_set.h:98:63: required from ‘class std::unordered_set’
solution.cc:119:51: required from here
/usr/include/c++/7/type_traits:154:31: error: ‘value’ is not a member of ‘std::__and_, std::__detail::__is_noexcept_hash >’
: public __bool_constant
^~~~~~~~~~~~~~~~
In file included from /usr/include/c++/7/unordered_set:48:0,
from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:118,
solution.cc:7:
/usr/include/c++/7/bits/unordered_set.h: In instantiation of ‘class std::unordered_set’:
solution.cc:119:51: required from here
/usr/include/c++/7/bits/unordered_set.h:98:63: error: ‘value’ is not a member of ‘std::__not_, std::__detail::__is_noexcept_hash > >’
typedef __uset_hashtable _Hashtable;
^~~~~~~~~~
/usr/include/c++/7/bits/unordered_set.h:105:45: error: ‘value’ is not a member of ‘std::__not_, std::__detail::__is_noexcept_hash > >’
typedef typename _Hashtable::key_type key_type;
^~~~~~~~

Список ошибок намного длиннее, я думаю, что этого может быть достаточно, чтобы кто-то мог понять ошибку. Я ссылался на эту страницу для пользовательских функций: http://thispointer.com/how-to-use-unordered_set-with-user-defined-classes-tutorial-example/. Есть предложения? Спасибо за чтение.

Редактировать 1: Создание неупорядоченного набора: 

unordered_set<Node,NodeHasher,NodeComparator> openList;

Редактировать 2: Ошибка в операторе сравнения. 

Player 1: compilation error
In file included from /usr/include/c++/7/bits/stl_algobase.h:71:0,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/bits/predefined_ops.h: In instantiation of ‘bool __gnu_cxx::__ops::_Iter_equals_val::operator()(_Iterator) [with _Iterator = __gnu_cxx::__normal_iterator >; _Value = const Node]’:
/usr/include/c++/7/bits/stl_algo.h:120:14: required from ‘_RandomAccessIterator std::__find_if(_RandomAccessIterator, _RandomAccessIterator, _Predicate, std::random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val]’
/usr/include/c++/7/bits/stl_algo.h:161:23: required from ‘_Iterator std::__find_if(_Iterator, _Iterator, _Predicate) [with _Iterator = __gnu_cxx::__normal_iterator >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val]’
/usr/include/c++/7/bits/stl_algo.h:3907:28: required from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator >; _Tp = Node]’
solution.cc:147:73: required from here
/usr/include/c++/7/bits/predefined_ops.h:241:17: error: no match for ‘operator==’ (operand types are ‘Node’ and ‘const Node’)
{ return *__it == _M_value; }
~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/bits/stl_iterator.h:859:5: note: candidate: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
operator==(const __normal_iterator& __lhs,
^~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:859:5: note: template argument deduction/substitution failed:
In file included from /usr/include/c++/7/bits/stl_algobase.h:71:0,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/bits/predefined_ops.h:241:17: note: ‘Node’ is not derived from ‘const __gnu_cxx::__normal_iterator’
{ return *__it == _M_value; }
~~~~~~^~~~~~~~~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/bits/stl_iterator.h:866:5: note: candidate: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
operator==(const __normal_iterator& __lhs,
^~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:866:5: note: template argument deduction/substitution failed:
In file included from /usr/include/c++/7/bits/stl_algobase.h:71:0,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/bits/predefined_ops.h:241:17: note: ‘Node’ is not derived from ‘const __gnu_cxx::__normal_iterator’
{ return *__it == _M_value; }
~~~~~~^~~~~~~~~~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/c++allocator.h:33:0,
from /usr/include/c++/7/bits/allocator.h:46,
from /usr/include/c++/7/vector:61,
solution.cc:3:
/usr/include/c++/7/ext/new_allocator.h:155:5: note: candidate: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)
operator==(const new_allocator&, const new_allocator&)
^~~~~~~~
/usr/include/c++/7/ext/new_allocator.h:155:5: note: template argument deduction/substitution failed:
In file included from /usr/include/c++/7/bits/stl_algobase.h:71:0,
from /usr/include/c++/7/vector:60,
solution.cc:3:
/usr/include/c++/7/bits/predefined_ops.h:241:17: note: ‘Node’ is not derived from ‘const __gnu_cxx::new_allocator’
{ return *__it == _M_value; }
~~~~~~^~~~~~~~~~~
solution.cc: In function ‘std::vector aStar(std::vector >&, std::pair, std::pair)’:
solution.cc:173:1: error: control reaches end of non-void function [-Werror=return-type]
}
^
cc1plus: some warnings being treated as errors

1 Ответ

0 голосов
/ 29 апреля 2018 
struct NodeHasher
{
  template <typename T, typename U>
  size_t const operator()(const Node &obj)
  {
    pair<T,U> position;
    position = obj.get_pos();
    return 3* std::hash<T>()(position.first) + std::hash<U>()(position.second) ;
  }
};

Компилятор может определить, что такое T и U в этом случае. Одним из решений будет удаление шаблона и жесткого кода int, поскольку вы знаете, что работаете с парой int.

И я полагаю, вы не поместили спецификатор const - он должен быть помещен в конце объявления

В качестве альтернативы, если вы хотите, чтобы NodeHasher работал для различных типов pair, вы можете вместо этого сделать его классом шаблона. 

template <typename T, typename U>
struct NodeHasher
{
    size_t operator()(const Node &obj) const
    {
        pair<T, U> position = obj.get_pos();
        return 3* std::hash<T>()(position.first) + std::hash<U>()(position.second) ;
    }
};

И создайте свой unordered_set как 

unordered_set<Node, NodeHasher<int,int>, NodeComparator> us; //T and U are int
...