C++：unordered_map，不可比較的迭代器

我有unordered_map，無法比較find()和end()返回的迭代器。這裏的情況：C++：unordered_map，不可比較的迭代器

unordered_map<IpAddressPort, uint32, IpAddressPortKey> current_sequence_numbers; 

... 

if (current_sequence_numbers.find(address) == current_sequence_numbers.end()) { 
    ... 
}

哪裏IpAddressPort只是一些struct和IpAddressPortKey看起來像這樣

struct IpAddressPortKey { 
    inline size_t operator()(const IpAddressPort &p) const { 
     return (p.type << 24 | p.addr_ipv4 | p.addr_ipv6.w1 | p.addr_ipv6.w2 
      | p.addr_ipv6.w3 | p.addr_ipv6.w4 | p.port); 
    } 
};

在if塊的比較給出這樣的錯誤：

/usr/include/c++/4.6/bits/hashtable.h:892:2: instantiated from ‘std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::_Node* std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::_M_find_node(std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::_Node*, const key_type&, typename std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::_Hash_code_type) const [with _Key = reload::IpAddressPort, _Value = std::pair<const reload::IpAddressPort, unsigned int>, _Allocator = std::allocator<std::pair<const reload::IpAddressPort, unsigned int> >, _ExtractKey = std::_Select1st<std::pair<const reload::IpAddressPort, unsigned int> >, _Equal = std::equal_to<reload::IpAddressPort>, _H1 = reload::IpAddressPortKey, _H2 = std::__detail::_Mod_range_hashing, _Hash = std::__detail::_Default_ranged_hash, _RehashPolicy = std::__detail::_Prime_rehash_policy, bool __cache_hash_code = false, bool __constant_iterators = false, bool __unique_keys = true, std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::_Node = std::__detail::_Hash_node<std::pair<const reload::IpAddressPort, unsigned int>, false>, std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::key_type = reload::IpAddressPort, typename std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::_Hash_code_type = unsigned int]’ 
/usr/include/c++/4.6/bits/hashtable.h:760:61: instantiated from ‘std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::iterator std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::find(const key_type&) [with _Key = reload::IpAddressPort, _Value = std::pair<const reload::IpAddressPort, unsigned int>, _Allocator = std::allocator<std::pair<const reload::IpAddressPort, unsigned int> >, _ExtractKey = std::_Select1st<std::pair<const reload::IpAddressPort, unsigned int> >, _Equal = std::equal_to<reload::IpAddressPort>, _H1 = reload::IpAddressPortKey, _H2 = std::__detail::_Mod_range_hashing, _Hash = std::__detail::_Default_ranged_hash, _RehashPolicy = std::__detail::_Prime_rehash_policy, bool __cache_hash_code = false, bool __constant_iterators = false, bool __unique_keys = true, std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::iterator = std::__detail::_Hashtable_iterator<std::pair<const reload::IpAddressPort, unsigned int>, false, false>, std::_Hashtable<_Key, _Value, _Allocator, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, __cache_hash_code, __constant_iterators, __unique_keys>::key_type = reload::IpAddressPort]’ 
link_management.cpp:134:51: instantiated from here 
/usr/include/c++/4.6/bits/stl_function.h:209:23: error: no match for ‘operator==’ in ‘__x == __y’ 
/usr/include/c++/4.6/bits/stl_function.h:209:23: note: candidates are: 
/usr/include/c++/4.6/bits/postypes.h:218:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&) 
/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template<class _T1, class _T2> constexpr bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) 
/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&) 
/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&) 
/usr/include/c++/4.6/bits/stl_iterator.h:1025:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&) 
/usr/include/c++/4.6/bits/stl_iterator.h:1031:5: note: template<class _Iterator> bool std::operator==(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&) 
/usr/include/c++/4.6/bits/allocator.h:122:5: note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_T1>&, const std::allocator<_T2>&) 
/usr/include/c++/4.6/bits/allocator.h:127:5: note: template<class _Tp> bool std::operator==(const std::allocator<_Tp1>&, const std::allocator<_Tp1>&) 
/usr/include/c++/4.6/bits/basic_string.h:2427:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&) 
/usr/include/c++/4.6/bits/basic_string.h:2434:5: note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&) 
/usr/include/c++/4.6/bits/basic_string.h:2448:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&) 
/usr/include/c++/4.6/bits/basic_string.h:2460:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*) 
/usr/include/c++/4.6/bits/streambuf_iterator.h:194:5: note: template<class _CharT, class _Traits> bool std::operator==(const std::istreambuf_iterator<_CharT, _Traits>&, const std::istreambuf_iterator<_CharT, _Traits>&) 
/usr/include/c++/4.6/bits/unordered_map.h:201:5: note: template<class _Key, class _Tp, class _Hash, class _Pred, class _Alloc, bool __cache_hash_code> bool std::operator==(const std::__unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc, __cache_hash_code>&, const std::__unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc, __cache_hash_code>&) 
/usr/include/c++/4.6/bits/unordered_map.h:219:5: note: template<class _Key, class _Tp, class _Hash, class _Pred, class _Alloc, bool __cache_hash_code> bool std::operator==(const std::__unordered_multimap<_Key, _Tp, _Hash, _Pred, _Alloc, __cache_hash_code>&, const std::__unordered_multimap<_Key, _Tp, _Hash, _Pred, _Alloc, __cache_hash_code>&) 
/usr/include/c++/4.6/bits/unordered_map.h:384:5: note: template<class _Key, class _Tp, class _Hash, class _Pred, class _Alloc> bool std::operator==(const std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>&, const std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>&) 
/usr/include/c++/4.6/bits/unordered_map.h:396:5: note: template<class _Key, class _Tp, class _Hash, class _Pred, class _Alloc> bool std::operator==(const std::unordered_multimap<_Key, _Tp, _Hash, _Pred, _Alloc>&, const std::unordered_multimap<_Key, _Tp, _Hash, _Pred, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_list.h:275:5: note: template<class _Val> bool std::operator==(const std::_List_iterator<_Tp>&, const std::_List_const_iterator<_Val>&) 
/usr/include/c++/4.6/bits/stl_list.h:1564:5: note: template<class _Tp, class _Alloc> bool std::operator==(const std::list<_Tp, _Alloc>&, const std::list<_Tp, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_deque.h:246:5: note: template<class _Tp, class _Ref, class _Ptr> bool std::operator==(const std::_Deque_iterator<_Tp, _Ref, _Ptr>&, const std::_Deque_iterator<_Tp, _Ref, _Ptr>&) 
/usr/include/c++/4.6/bits/stl_deque.h:253:5: note: template<class _Tp, class _RefL, class _PtrL, class _RefR, class _PtrR> bool std::operator==(const std::_Deque_iterator<_Tp, _RefL, _PtrL>&, const std::_Deque_iterator<_Tp, _RefR, _PtrR>&) 
/usr/include/c++/4.6/bits/stl_deque.h:1917:5: note: template<class _Tp, class _Alloc> bool std::operator==(const std::deque<_Tp, _Alloc>&, const std::deque<_Tp, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_tree.h:309:5: note: template<class _Val> bool std::operator==(const std::_Rb_tree_iterator<_Tp>&, const std::_Rb_tree_const_iterator<_Val>&) 
/usr/include/c++/4.6/bits/stl_tree.h:846:5: note: template<class _Key, class _Val, class _KeyOfValue, class _Compare, class _Alloc> bool std::operator==(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_map.h:877:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator==(const std::map<_Key, _Tp, _Compare, _Alloc>&, const std::map<_Key, _Tp, _Compare, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_multimap.h:795:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator==(const std::multimap<_Key, _Tp, _Compare, _Alloc>&, const std::multimap<_Key, _Tp, _Compare, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_set.h:696:5: note: template<class _Key, class _Compare, class _Alloc> bool std::operator==(const std::set<_Key, _Compare, _Alloc>&, const std::set<_Key, _Compare, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_multiset.h:679:5: note: template<class _Key, class _Compare, class _Alloc> bool std::operator==(const std::multiset<_Key, _Compare, _Alloc>&, const std::multiset<_Key, _Compare, _Alloc>&) 
/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template<class _Tp, class _Alloc> bool std::operator==(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)

任何想法可能是什麼導致這個？

來源

2011-12-24 aRestless

您能否提供其餘的錯誤？這顯然只是在實施中，而不是那條線的完全錯誤，我不認爲。 – lefticus 2011-12-24 07:20:22

@lefticus：done – aRestless 2011-12-24 14:05:14

看來您還沒有爲IpAddressPort類定義operator==()。你應該定義operator==或定義權益仿函數並將其作爲第4個模板參數提供

來源

2011-12-24 07:49:24 Eugene

比較迭代器（而不是它們指向的結構）時，這怎麼會是這個原因？ 'end（）'甚至沒有指向一個有效的結構，因爲它是一個指示元素找不到。 – aRestless 2011-12-24 13:57:12

這個答案是正確的，我自己測試了一下。我無法在標準中找到任何具體說明unordered_map要求密鑰相等的情況。我知道，在std :: map中的鍵需要少於可比（這是有道理的，因爲它們是有序的）。 – lefticus 2011-12-24 15:31:41

@lefticus：顯然，無序映射需要對元素進行相等比較才能實現散列表。這個推理在標準中可能並不明確，但是可以肯定的是平等可比的要求。 – 2011-12-24 15:44:57

C++：unordered_map，不可比較的迭代器

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