从 'std：:p air<std：：_Rb_tree_iterator<_Val>， bool> std：：_Rb_tree<_Key， _Val， _KeyOfVa

我遇到了汇编错误，

required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = Solution::EnhancedNode* const&; _Key = Solution::EnhancedNode*; _Val = Solution::EnhancedNode*; _KeyOfValue = std::_Identity<Solution::EnhancedNode*>; _Compare = Solution::EnhancedNodeComparator; _Alloc = std::allocator<Solution::EnhancedNode*>]'

不幸的是，没有行号，但是我的删除代码部分，我相信这与我想将自定义比较器应用于以下方式的std::set有关：

class EnhancedNode {
public:
    EnhancedNode(TreeNode* node) {
        node_ = node;
        distance_ = numeric_limits<double>::max();
        discarded_ = false;
    }
    TreeNode* node_;
    double distance_;
    bool discarded_;
};
struct EnhancedNodeComparator {
    bool operator() (const EnhancedNode*& a, const EnhancedNode*& b) const {
        return a->distance_ < b->distance_;
    }
};
set<EnhancedNode*, EnhancedNodeComparator> closest_;
set<EnhancedNode*, EnhancedNodeComparator> next_;

我在做什么显然错误的吗？

std::set的比较器绝对应接受集合中的const合格类型的引用。

您出错的是集合中类型的资格。它是EnhancedNode*，因此使用const限定它应该给出EnhancedNode* const。而不是const EnhancedNode*。

这再次是领导const误导的案例。用参考和全部更改您的原始比较器：

struct EnhancedNodeComparator {
    bool operator() (EnhancedNode const * const& a, EnhancedNode const * const& b) const {
        return a->distance_ < b->distance_;
    }
};

您也可以保留构成资格的点。由于C 明确允许。

当您摆脱参考时，您的问题是解决的，这是因为在通过值传递时忽略了顶级const。因此，您的函数接收到的指针无关紧要，因为参数没有资格。它只是原始的副本。

创建最小，完整，可验证的^tm示例，我能够解决我的问题。无论如何，我都会发布它，因为Google出奇的引号中错误的第一部分的命中率为零。

事实证明，我不需要

中的 & s

struct EnhancedNodeComparator {
    bool operator() (const EnhancedNode*& a, const EnhancedNode*& b) const {

我通过在其他编译器上编译http://cpp.sh，

来找到这一点。

#include <limits>
#include <set>
using namespace std;
struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};
class EnhancedNode {
public:
    EnhancedNode(TreeNode* node) {
        node_ = node;
        distance_ = numeric_limits<double>::max();
        discarded_ = false;
    }
    TreeNode* node_;
    double distance_;
    bool discarded_;
};
struct EnhancedNodeComparator {
    bool operator() (const EnhancedNode*& a, const EnhancedNode*& b) const {
        return a->distance_ < b->distance_;
    }
};
int main()
{
    set<EnhancedNode*, EnhancedNodeComparator> closest_;
    closest_.insert(new EnhancedNode(new TreeNode(1)));
    return 0;
}

并遇到一个更有帮助的错误：

In file included from /usr/include/c++/4.9/set:60:0,
                 from 3:
/usr/include/c++/4.9/bits/stl_tree.h: In instantiation of 'std::pair<std::_Rb_tree_node_base*, std::_Rb_tree_node_base*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_get_insert_unique_pos(const key_type&) [with _Key = EnhancedNode*; _Val = EnhancedNode*; _KeyOfValue = std::_Identity<EnhancedNode*>; _Compare = EnhancedNodeComparator; _Alloc = std::allocator<EnhancedNode*>; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::key_type = EnhancedNode*]':
/usr/include/c++/4.9/bits/stl_tree.h:1498:47:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = EnhancedNode*; _Key = EnhancedNode*; _Val = EnhancedNode*; _KeyOfValue = std::_Identity<EnhancedNode*>; _Compare = EnhancedNodeComparator; _Alloc = std::allocator<EnhancedNode*>]'
/usr/include/c++/4.9/bits/stl_set.h:511:40:   required from 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(std::set<_Key, _Compare, _Alloc>::value_type&&) [with _Key = EnhancedNode*; _Compare = EnhancedNodeComparator; _Alloc = std::allocator<EnhancedNode*>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree_const_iterator<EnhancedNode*>; std::set<_Key, _Compare, _Alloc>::value_type = EnhancedNode*]'
33:54:   required from here
/usr/include/c++/4.9/bits/stl_tree.h:1445:11: error: no match for call to '(EnhancedNodeComparator) (EnhancedNode* const&, EnhancedNode* const&)'
    __comp = _M_impl._M_key_compare(__k, _S_key(__x));
           ^
24:8: note: candidate is:
25:10: note: bool EnhancedNodeComparator::operator()(const EnhancedNode*&, const EnhancedNode*&) const
25:10: note:   no known conversion for argument 1 from 'const key_type {aka EnhancedNode* const}' to 'const EnhancedNode*&'
In file included from /usr/include/c++/4.9/set:60:0,
                 from 3:
/usr/include/c++/4.9/bits/stl_tree.h:1456:7: error: no match for call to '(EnhancedNodeComparator) (EnhancedNode* const&, EnhancedNode* const&)'
       if (_M_impl._M_key_compare(_S_key(__j._M_node), __k))
       ^
24:8: note: candidate is:
25:10: note: bool EnhancedNodeComparator::operator()(const EnhancedNode*&, const EnhancedNode*&) const
25:10: note:   no known conversion for argument 1 from 'EnhancedNode* const' to 'const EnhancedNode*&'
In file included from /usr/include/c++/4.9/set:60:0,
                 from 3:
/usr/include/c++/4.9/bits/stl_tree.h: In instantiation of 'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Base_ptr, std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Base_ptr, _Arg&&) [with _Arg = EnhancedNode*; _Key = EnhancedNode*; _Val = EnhancedNode*; _KeyOfValue = std::_Identity<EnhancedNode*>; _Compare = EnhancedNodeComparator; _Alloc = std::allocator<EnhancedNode*>; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator = std::_Rb_tree_iterator<EnhancedNode*>; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Base_ptr = std::_Rb_tree_node_base*]':
/usr/include/c++/4.9/bits/stl_tree.h:1502:38:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = EnhancedNode*; _Key = EnhancedNode*; _Val = EnhancedNode*; _KeyOfValue = std::_Identity<EnhancedNode*>; _Compare = EnhancedNodeComparator; _Alloc = std::allocator<EnhancedNode*>]'
/usr/include/c++/4.9/bits/stl_set.h:511:40:   required from 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(std::set<_Key, _Compare, _Alloc>::value_type&&) [with _Key = EnhancedNode*; _Compare = EnhancedNodeComparator; _Alloc = std::allocator<EnhancedNode*>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree_const_iterator<EnhancedNode*>; std::set<_Key, _Compare, _Alloc>::value_type = EnhancedNode*]'
33:54:   required from here
/usr/include/c++/4.9/bits/stl_tree.h:1140:8: error: no match for call to '(EnhancedNodeComparator) (EnhancedNode*&, EnhancedNode* const&)'
        || _M_impl._M_key_compare(_KeyOfValue()(__v),
        ^
24:8: note: candidate is:
25:10: note: bool EnhancedNodeComparator::operator()(const EnhancedNode*&, const EnhancedNode*&) const
25:10: note:   no known conversion for argument 1 from 'EnhancedNode*' to 'const EnhancedNode*&'

我不太了解为什么是这样。我在网上发现的STD :: SET的自定义比较器的所有示例似乎都添加了&。如果有人可以解释为答案，我会选择它作为完整的答案。

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