std :: mapをstd :: list :: iteratorで使用する

Question

なぜこのコードはコンパイルされませんか？

#include <map> 
#include <list> 

int main() 
{ 
    typedef std::list<int>::iterator Iter; 

    std::map<Iter, Iter> m; 

    std::list<int> ints; 

    m[ints.begin()] = ints.begin(); 
} 

私はstd::vectorためstd::listを変更すると、すべてが動作します。

次のようにエラーログがある：

|| "==== Building Practical (release) ====" 
|| main.cpp 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
|| C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_function.h: In instantiation of 'bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = std::_List_iterator<int>]': 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_map.h|498 col 32| required from 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](std::map<_Key, _Tp, _Compare, _Alloc>::key_type&&) [with _Key = std::_List_iterator<int>; _Tp = std::_List_iterator<int>; _Compare = std::less<std::_List_iterator<int> >; _Alloc = std::allocator<std::pair<const std::_List_iterator<int>, std::_List_iterator<int> > >; std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = std::_List_iterator<int>; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = std::_List_iterator<int>]' 
main.cpp|12 col 19| required from here 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| error: no match for 'operator<' (operand types are 'const std::_List_iterator<int>' and 'const std::_List_iterator<int>') 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_algobase.h|64| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_tree.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_pair.h|220 col 5| note: candidate: template<class _T1, class _T2> constexpr bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) 
||  operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y) 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_pair.h|220 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::pair<_T1, _T2>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_algobase.h|67| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_tree.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|298 col 5| note: candidate: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&) 
||  operator<(const reverse_iterator<_Iterator>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|298 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::reverse_iterator<_Iterator>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_algobase.h|67| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_tree.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|348 col 5| note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&) 
||  operator<(const reverse_iterator<_IteratorL>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|348 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::reverse_iterator<_Iterator>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_algobase.h|67| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_tree.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|1089 col 5| note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_IteratorR>&) 
||  operator<(const move_iterator<_IteratorL>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|1089 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::move_iterator<_Iterator>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_algobase.h|67| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_tree.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|1095 col 5| note: candidate: template<class _Iterator> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&) 
||  operator<(const move_iterator<_Iterator>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_iterator.h|1095 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::move_iterator<_Iterator>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\map|60| 0, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|1293 col 5| note: candidate: 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>&) 
||  operator<(const _Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|1293 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\string|52| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/stdexcept:39, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/array:38, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/tuple:39, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_map.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:61, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\basic_string.h|4982 col 5| note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) 
||  operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\basic_string.h|4982 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\string|52| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/stdexcept:39, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/array:38, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/tuple:39, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_map.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:61, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\basic_string.h|4994 col 5| note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*) 
||  operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\basic_string.h|4994 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\string|52| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/stdexcept:39, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/array:38, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/tuple:39, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_map.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:61, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\basic_string.h|5006 col 5| note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) 
||  operator<(const _CharT* __lhs, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\basic_string.h|5006 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: mismatched types 'const _CharT*' and 'std::_List_iterator<int>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\tuple|39| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/bits/stl_map.h:63, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:61, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\array|242 col 5| note: candidate: template<class _Tp, unsigned int _Nm> bool std::operator<(const std::array<_Tp, _Nm>&, const std::array<_Tp, _Nm>&) 
||  operator<(const array<_Tp, _Nm>& __a, const array<_Tp, _Nm>& __b) 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\array|242 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::array<_Tp, _Nm>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_map.h|63| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:61, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\tuple|928 col 5| note: candidate: template<class ... _TElements, class ... _UElements> constexpr bool std::operator<(const std::tuple<_Args1 ...>&, const std::tuple<_Args2 ...>&) 
||  operator<(const tuple<_TElements...>& __t, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\tuple|928 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::tuple<_Args1 ...>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\map|61| 0, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_map.h|1087 col 5| note: candidate: 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>&) 
||  operator<(const map<_Key, _Tp, _Compare, _Alloc>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_map.h|1087 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::map<_Key, _Tp, _Compare, _Alloc>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\map|62| 0, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_multimap.h|988 col 5| note: candidate: 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>&) 
||  operator<(const multimap<_Key, _Tp, _Compare, _Alloc>& __x, 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_multimap.h|988 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::multimap<_Key, _Tp, _Compare, _Alloc>' 
||  { return __x < __y; } 
||     ^
In file included from C:\mingw32\i686-w64-mingw32\include\c++\list|63| 0, 
||     from ../src/main.cpp:2: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_list.h|1836 col 5| note: candidate: template<class _Tp, class _Alloc> bool std::operator<(const std::__cxx11::list<_Tp, _Alloc>&, const std::__cxx11::list<_Tp, _Alloc>&) 
||  operator<(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y) 
|| ^
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_list.h|1836 col 5| note: template argument deduction/substitution failed: 
In file included from C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_tree.h|65| 0, 
||     from C:/mingw32/i686-w64-mingw32/include/c++/map:60, 
||     from ../src/main.cpp:1: 
C:\mingw32\i686-w64-mingw32\include\c++\bits\stl_function.h|387 col 20| note: 'const std::_List_iterator<int>' is not derived from 'const std::__cxx11::list<_Tp, _Alloc>' 
||  { return __x < __y; } 
||     ^
Practical.make|106| recipe for target 'obj/Release/main.o' failed 
|| mingw32-make.exe[1]: *** [obj/Release/main.o] Error 1 
makefile|16| recipe for target 'Practical' failed 
|| mingw32-make.exe: *** [Practical] Error 2 

StackOverflowのは、私のメッセージはほとんどのコードですので、私はここに、この文を記述する必要が私に語りました。

Answer 1

std::listイテレータは、bidirectional iteratorsです。彼らはrandom access iteratorsのような比較をサポートしていません。

std::mapについては、がとなっているため、比較が必要です。マップはキーでソートされています。このソートが機能するには、キーを比較できる必要があります。前述したように、リストイテレータはそうではありません。

注文しない場合は、代わりにstd::unordered_mapを使用してください。一方、Angewが指摘したように、std::unordered_mapはハッシュされたコンテナであり、動作させるにはstd::hashの特殊化が必要です。