如何在unordered_set hasher的自定义类对象的函数中求解此错误
How to solve this error in unordered_set hasher function of custom class objects?
我首次使用无序的地图，并使用自定义对象。我试图写下以下功能。有一些我需要帮助的错误。
这是类。
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;
}
};
以下是自定义功能：
// 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;
}
};
我得到以下错误：
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;
^~~~~~~~
错误列表更长，我认为这可能足以让某人理解错误。我将此页面引用了自定义函数：http：//thispointer.com/how-to-use-usordorded_set-with-user-defined-classes-tutorial-example/。有什么建议么？感谢您的阅读。
编辑1：unordered_set创建：
unordered_set<Node,NodeHasher,NodeComparator> openList;
编辑2：比较操作员的错误。
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
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) ;
}
};
在这种情况下，编译器可以推断出T和U是什么。一种解决方案是删除模板和硬码int，因为您知道自己正在使用一对int。
我相信您放错了const指示符 - 应该放置在声明的末尾
另外，如果要使Nodehasher适用于不同类型的pair，则可以使其成为模板类。
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) ;
}
};
并将您的unordered_set创建为
unordered_set<Node, NodeHasher<int,int>, NodeComparator> us; //T and U are int
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