STD::reverse_iterator

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这篇博客探讨了std::reverse_iterator的概念，它是一个迭代器适配器，用于反转给定迭代器的方向。reverse_iterator从双向迭代器创建时，会提供一个从结束到开始的迭代顺序。内容中提到，对于由iterator构造的reverse_iterator，其关系&*r == &*(i-1)总是成立。reverse_iterator在++和--操作时的行为与常规相反，这使得它可以用于反向遍历序列。文章通过代码示例和参考资料帮助读者理解其工作原理。

阅读STL代码的时候，看到STD::reverse_iterator不是很懂，就查了一些资料。

std::reverse_iterator is an iterator adaptor that reverses the direction of a given iterator. In other words, when provided with a bidirectional iterator, std::reverse_iterator produces a new iterator that moves from the end to the beginning of the sequence defined by the underlying bidirectional iterator.

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C++：反向迭代器reverse_iterator
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是 C++ 标准库中的一个迭代器适配器（iterator adapter），它允许你以反向顺序遍历容器或序列。这个适配器通过封装一个基础迭代器（通常是正向迭代器）并提供反向的递增（++）和递减（--）操作来实现这一功能。当你递增一个时，它实际上是在递减其封装的基础迭代器，反之亦然。通常用于需要反向遍历容器的场景，比如从后向前打印容器中的元素。
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chromium code 1: // base\containers\mru_cache.h 中 2: // MRUCache entries are often processed in reverse order, so we add this 3: // convenience function (not typically defined by STL containers). ...
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本篇目的：C++进阶之反向迭代器std::reverse_iterator：用法实例基本概念是 C++ 标准库提供的一种适配器，用于将任意支持双向或随机访问的迭代器转换为反向迭代器，使其从容器的尾部向头部进行遍历。它封装了一个底层迭代器，并通过调整递增与递减行为实现逆序访问。特性与接口提供标准迭代器的接口，包括解引用（）、递增（++）、递减（--）、偏移访问（）、比较操作（==!等），前提是底层迭代器支持相应操作。解引用时，返回的是其内部迭代器前一个位置的值，以符合逆序语义。与普通迭代器的区别。
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描述：        逆转容器中的元素顺序。 定义： template< class BidirIt > void reverse( BidirIt first, BidirIt last ); template< class BidirIt > constexpr void reverse( BidirIt first, BidirIt last ); 可能的实现： template<class BidirIt> void r
In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h: In instantiation of ‘constexpr bool __gnu_cxx::__ops::_Iter_less_iter::operator()(_Iterator1, _Iterator2) const [with _Iterator1 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Iterator2 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’: /usr/include/c++/11/bits/stl_algo.h:5624:12: required from ‘constexpr _ForwardIterator std::__min_element(_ForwardIterator, _ForwardIterator, _Compare) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’ /usr/include/c++/11/bits/stl_algo.h:5648:43: required from ‘constexpr _FIter std::min_element(_FIter, _FIter) [with _FIter = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ a.cpp:46:27: required from here /usr/include/c++/11/bits/predefined_ops.h:45:23: error: no match for ‘operator<’ (operand types are ‘std::pair<double, Point>’ and ‘std::pair<double, Point>’) 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/stl_algobase.h:67, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/stl_iterator.h:1129:5: note: candidate: ‘template<class _IteratorL, class _IteratorR, class _Container> constexpr std::__detail::__synth3way_t<_IteratorR, _IteratorL> __gnu_cxx::operator<=>(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)’ (reversed) 1129 | operator<=>(const __normal_iterator<_IteratorL, _Container>& __lhs, | ^~~~~~~~ /usr/include/c++/11/bits/stl_iterator.h:1129:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const __gnu_cxx::__normal_iterator<_IteratorL, _Container>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/stl_algobase.h:67, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/stl_iterator.h:538:5: note: candidate: ‘template<class _IteratorL, class _IteratorR> requires three_way_comparable_with<_IteratorR, _IteratorL, std::partial_ordering> constexpr std::compare_three_way_result_t<_IteratorL, _IteratorR> std::operator<=>(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)’ (reversed) 538 | operator<=>(const reverse_iterator<_IteratorL>& __x, | ^~~~~~~~ /usr/include/c++/11/bits/stl_iterator.h:538:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::reverse_iterator<_IteratorL>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/stl_algobase.h:67, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/stl_iterator.h:1596:5: note: candidate: ‘template<class _IteratorL, class _IteratorR> requires three_way_comparable_with<_IteratorR, _IteratorL, std::partial_ordering> constexpr std::compare_three_way_result_t<_IteratorL, _IteratorR> std::operator<=>(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)’ (reversed) 1596 | operator<=>(const move_iterator<_IteratorL>& __x, | ^~~~~~~~ /usr/include/c++/11/bits/stl_iterator.h:1596:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::move_iterator<_IteratorL>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/basic_string.h:48, from /usr/include/c++/11/string:55, from /usr/include/c++/11/bits/locale_classes.h:40, from /usr/include/c++/11/bits/ios_base.h:41, from /usr/include/c++/11/ios:42, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/string_view:556:5: note: candidate: ‘template<class _CharT, class _Traits> constexpr decltype (__char_traits_cmp_cat<_Traits>(0)) std::operator<=>(std::basic_string_view<_CharT, _Traits>, std::__type_identity_t<std::basic_string_view<_CharT, _Traits> >)’ (reversed) 556 | operator<=>(basic_string_view<_CharT, _Traits> __x, | ^~~~~~~~ /usr/include/c++/11/string_view:556:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘std::basic_string_view<_CharT, _Traits>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/string:55, from /usr/include/c++/11/bits/locale_classes.h:40, from /usr/include/c++/11/bits/ios_base.h:41, from /usr/include/c++/11/ios:42, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/basic_string.h:6276:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> decltype (__char_traits_cmp_cat<_Traits>(0)) std::operator<=>(const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)’ (reversed) 6276 | operator<=>(const basic_string<_CharT, _Traits, _Alloc>& __lhs, | ^~~~~~~~ /usr/include/c++/11/bits/basic_string.h:6276:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/unique_ptr.h:37, from /usr/include/c++/11/bits/locale_conv.h:41, from /usr/include/c++/11/locale:43, from /usr/include/c++/11/iomanip:43, from a.cpp:4: /usr/include/c++/11/tuple:1557:5: note: candidate: ‘template<class ... _Tps, class ... _Ups> constexpr std::common_comparison_category_t<decltype (std::__detail::__synth3way(declval<_Tps&>(), declval<_Ups&>()))...> std::operator<=>(const std::tuple<_Tps ...>&, const std::tuple<_UTypes ...>&)’ (reversed) 1557 | operator<=>(const tuple<_Tps...>& __t, const tuple<_Ups...>& __u) | ^~~~~~~~ /usr/include/c++/11/tuple:1557:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::tuple<_Tps ...>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/locale_conv.h:41, from /usr/include/c++/11/locale:43, from /usr/include/c++/11/iomanip:43, from a.cpp:4: /usr/include/c++/11/bits/unique_ptr.h:895:5: note: candidate: ‘template<class _Tp, class _Dp, class _Up, class _Ep> requires three_way_comparable_with<typename std::unique_ptr<_Tp, _Dp>::pointer, typename std::unique_ptr<_Up, _Ep>::pointer, std::partial_ordering> std::compare_three_way_result_t<typename std::unique_ptr<_Tp, _Dp>::pointer, typename std::unique_ptr<_Up, _Ep>::pointer> std::operator<=>(const std::unique_ptr<_Tp, _Dp>&, const std::unique_ptr<_Up, _Ep>&)’ (reversed) 895 | operator<=>(const unique_ptr<_Tp, _Dp>& __x, | ^~~~~~~~ /usr/include/c++/11/bits/unique_ptr.h:895:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::unique_ptr<_Tp, _Dp>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/locale_conv.h:41, from /usr/include/c++/11/locale:43, from /usr/include/c++/11/iomanip:43, from a.cpp:4: /usr/include/c++/11/bits/unique_ptr.h:903:5: note: candidate: ‘template<class _Tp, class _Dp> requires three_way_comparable<typename std::unique_ptr<_Tp, _Dp>::pointer, std::partial_ordering> std::compare_three_way_result_t<typename std::unique_ptr<_Tp, _Dp>::pointer> std::operator<=>(const std::unique_ptr<_Tp, _Dp>&, std::nullptr_t)’ (reversed) 903 | operator<=>(const unique_ptr<_Tp, _Dp>& __x, nullptr_t) | ^~~~~~~~ /usr/include/c++/11/bits/unique_ptr.h:903:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::unique_ptr<_Tp, _Dp>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/stl_algobase.h:67, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/stl_iterator.h:1146:5: note: candidate: ‘template<class _Iterator, class _Container> constexpr std::__detail::__synth3way_t<_T1> __gnu_cxx::operator<=>(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)’ (rewritten) 1146 | operator<=>(const __normal_iterator<_Iterator, _Container>& __lhs, | ^~~~~~~~ /usr/include/c++/11/bits/stl_iterator.h:1146:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const __gnu_cxx::__normal_iterator<_Iterator, _Container>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/stl_algobase.h:64, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/stl_pair.h:473:5: note: candidate: ‘template<class _T1, class _T2> constexpr std::common_comparison_category_t<decltype (std::__detail::__synth3way(declval<_T1&>(), declval<_T1&>())), decltype (std::__detail::__synth3way(declval<_T2&>(), declval<_T2&>()))> std::operator<=>(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)’ (rewritten) 473 | operator<=>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y) | ^~~~~~~~ /usr/include/c++/11/bits/stl_pair.h:473:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_pair.h:65, from /usr/include/c++/11/bits/stl_algobase.h:64, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/compare: In substitution of ‘template<class _T1, class _T2> constexpr std::common_comparison_category_t<decltype (std::__detail::__synth3way(declval<_T1&>(), declval<_T1&>())), decltype (std::__detail::__synth3way(declval<_T2&>(), declval<_T2&>()))> std::operator<=>(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) [with _T1 = double; _T2 = Point]’: /usr/include/c++/11/bits/predefined_ops.h:45:23: required from ‘constexpr bool __gnu_cxx::__ops::_Iter_less_iter::operator()(_Iterator1, _Iterator2) const [with _Iterator1 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Iterator2 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ /usr/include/c++/11/bits/stl_algo.h:5624:12: required from ‘constexpr _ForwardIterator std::__min_element(_ForwardIterator, _ForwardIterator, _Compare) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’ /usr/include/c++/11/bits/stl_algo.h:5648:43: required from ‘constexpr _FIter std::min_element(_FIter, _FIter) [with _FIter = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ a.cpp:46:27: required from here /usr/include/c++/11/compare:915:41: error: no match for call to ‘(const std::__detail::_Synth3way) (Point&, Point&)’ 915 | = decltype(__detail::__synth3way(std::declval<_Tp&>(), | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~ 916 | std::declval<_Up&>())); | ~~~~~~~~~~~~~~~~~~~~~ /usr/include/c++/11/compare:890:9: note: candidate: ‘template<class _Tp, class _Up> constexpr auto std::__detail::_Synth3way::operator()(const _Tp&, const _Up&) const requires requires{{std::__detail::_Synth3way::operator()::__t < std::__detail::_Synth3way::operator()::__u} -> decltype(auto) [requires std::__detail::__boolean_testable<<placeholder>, >];{std::__detail::_Synth3way::operator()::__u < std::__detail::_Synth3way::operator()::__t} -> decltype(auto) [requires std::__detail::__boolean_testable<<placeholder>, >];}’ 890 | operator()(const _Tp& __t, const _Up& __u) const | ^~~~~~~~ /usr/include/c++/11/compare:890:9: note: template argument deduction/substitution failed: /usr/include/c++/11/compare:890:9: note: constraints not satisfied /usr/include/c++/11/compare: In substitution of ‘template<class _Tp, class _Up> constexpr auto std::__detail::_Synth3way::operator()(const _Tp&, const _Up&) const requires requires{{__t < __u} -> decltype(auto) [requires std::__detail::__boolean_testable<<placeholder>, >];{__u < __t} -> decltype(auto) [requires std::__detail::__boolean_testable<<placeholder>, >];} [with _Tp = Point; _Up = Point]’: /usr/include/c++/11/compare:915:34: required by substitution of ‘template<class _T1, class _T2> constexpr std::common_comparison_category_t<decltype (std::__detail::__synth3way(declval<_T1&>(), declval<_T1&>())), decltype (std::__detail::__synth3way(declval<_T2&>(), declval<_T2&>()))> std::operator<=>(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) [with _T1 = double; _T2 = Point]’ /usr/include/c++/11/bits/predefined_ops.h:45:23: required from ‘constexpr bool __gnu_cxx::__ops::_Iter_less_iter::operator()(_Iterator1, _Iterator2) const [with _Iterator1 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Iterator2 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ /usr/include/c++/11/bits/stl_algo.h:5624:12: required from ‘constexpr _ForwardIterator std::__min_element(_ForwardIterator, _ForwardIterator, _Compare) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’ /usr/include/c++/11/bits/stl_algo.h:5648:43: required from ‘constexpr _FIter std::min_element(_FIter, _FIter) [with _FIter = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ a.cpp:46:27: required from here /usr/include/c++/11/compare:890:2: required by the constraints of ‘template<class _Tp, class _Up> constexpr auto std::__detail::_Synth3way::operator()(const _Tp&, const _Up&) const requires requires{{__t < __u} -> decltype(auto) [requires std::__detail::__boolean_testable<<placeholder>, >];{__u < __t} -> decltype(auto) [requires std::__detail::__boolean_testable<<placeholder>, >];}’ /usr/include/c++/11/compare:892:11: in requirements [with _Up = Point; _Tp = Point] /usr/include/c++/11/compare:894:17: note: the required expression ‘(__t < __u)’ is invalid 894 | { __t < __u } -> __boolean_testable; | ~~~~^~~~~ /usr/include/c++/11/compare:895:17: note: the required expression ‘(__u < __t)’ is invalid 895 | { __u < __t } -> __boolean_testable; | ~~~~^~~~~ /usr/include/c++/11/compare: In substitution of ‘template<class _T1, class _T2> constexpr std::common_comparison_category_t<decltype (std::__detail::__synth3way(declval<_T1&>(), declval<_T1&>())), decltype (std::__detail::__synth3way(declval<_T2&>(), declval<_T2&>()))> std::operator<=>(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) [with _T1 = double; _T2 = Point]’: /usr/include/c++/11/bits/predefined_ops.h:45:23: required from ‘constexpr bool __gnu_cxx::__ops::_Iter_less_iter::operator()(_Iterator1, _Iterator2) const [with _Iterator1 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Iterator2 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ /usr/include/c++/11/bits/stl_algo.h:5624:12: required from ‘constexpr _ForwardIterator std::__min_element(_ForwardIterator, _ForwardIterator, _Compare) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’ /usr/include/c++/11/bits/stl_algo.h:5648:43: required from ‘constexpr _FIter std::min_element(_FIter, _FIter) [with _FIter = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ a.cpp:46:27: required from here cc1plus: note: set ‘-fconcepts-diagnostics-depth=’ to at least 2 for more detail In file included from /usr/include/c++/11/bits/stl_algobase.h:67, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h: In instantiation of ‘constexpr bool __gnu_cxx::__ops::_Iter_less_iter::operator()(_Iterator1, _Iterator2) const [with _Iterator1 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Iterator2 = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’: /usr/include/c++/11/bits/stl_algo.h:5624:12: required from ‘constexpr _ForwardIterator std::__min_element(_ForwardIterator, _ForwardIterator, _Compare) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’ /usr/include/c++/11/bits/stl_algo.h:5648:43: required from ‘constexpr _FIter std::min_element(_FIter, _FIter) [with _FIter = __gnu_cxx::__normal_iterator<std::pair<double, Point>*, std::vector<std::pair<double, Point> > >]’ a.cpp:46:27: required from here /usr/include/c++/11/bits/stl_iterator.h:554:5: note: candidate: ‘template<class _Iterator> requires three_way_comparable<_Iterator, std::partial_ordering> constexpr std::compare_three_way_result_t<_Iterator, _Iterator> std::operator<=>(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorL>&)’ (rewritten) 554 | operator<=>(const reverse_iterator<_Iterator>& __x, | ^~~~~~~~ /usr/include/c++/11/bits/stl_iterator.h:554:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::reverse_iterator<_IteratorL>’ 45 | { return *__it1 < *__it2; } | ~~~~~~~^~~~~~~~ In file included from /usr/include/c++/11/bits/stl_algobase.h:67, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/stl_iterator.h:1655:5: note: candidate: ‘template<class _Iterator> requires three_way_comparable<_Iterator, std::partial_ordering> constexpr std::compare_three_way_result_t<_Iterator, _Iterator> std::operator<=>(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)’ (rewritten) 1655 | operator<=>(const move_iterator<_Iterator>& __x, | ^~~~~~~~ /usr/include/c++/11/bits/stl_iterator.h:1655:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/11/bits/stl_algobase.h:71, from /usr/include/c++/11/bits/char_traits.h:39, from /usr/include/c++/11/ios:40, from /usr/include/c++/11/ostream:38, from /usr/include/c++/11/iostream:39, from a.cpp:1: /usr/include/c++/11/bits/predefined_ops.h:45:23: note: ‘std::pair<double, Point>’ is not derived from ‘const std::move_iterator<_IteratorL>’根据报错修改
最新发布
01-04
错误原因是：`std::min_element` 无法比较 `std::pair, Point>` 类型，因为 `Point` 没有定义 `或 `运算符。虽然 `double` 可以比较，但 `std::pair` 的默认比较会尝试递归比较第二个成员 `Point`，而 `Point` 不...
20 39 C:\Users\Administrator\Desktop\?疵?名9.cpp [Error] conversion from 'std::map<int, int>::reverse_iterator' {aka 'std::reverse_iterator<std::_Rb_tree_iterator<std::pair<const int, int> > >'} to non-scalar type 'std::map<int, int>::iterator' {aka 'std::_Rb_tree_iterator<std::pair<const int, int> >'} requested
07-27
根据引用[1][2][3]，我们知道反向迭代器是通过`std::reverse_iterator`模板实现的，它包装了一个正向迭代器，但移动方向相反。 在C++标准库中，反向迭代器提供了`base()`成员函数来获取其对应的底层正向迭代器。...
error: no match for ‘operator!=’ (operand types are ‘std::vector<int>::iterator {aka __gnu_cxx::__normal_iterator<int*, std::vector<int> >}’ and ‘std::vector<int>::reverse_iterator {aka std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >}’)
05-25
std::vector<int>::iterator 是正向迭代器，而std::vector<int>::reverse_iterator 是反向迭代器，它们的底层实现是不同的。 如果你需要比较两个不同类型的迭代器，可以将其中一个迭代器转换为另一个类型的迭代器。...
// 答题框内的代码仅为待实现代码，执行或提交代码时，仅包含待实现部分，不要包含其它代码。 // CodeCheck/Cmetrics工具也仅扫描待实现部分。 // 若需要完整框架用于本地调试，请点击答题框上面的“下载完整框架代码”进行下载。 #include <string> #include <vector> #include <map> using namespace std; struct Compare { bool operator()(const pair<int, vector<int>>& p1, const pair<int, vector<int>>& p2) const{ if ( p1.first != p2.first) { return p1.first < p2.first; } else { for (int i = 0 ; i < p1.second.size(); ++i) { if ((p1.second)[i] != (p2.second)[i]) return (p1.second)[i] < (p2.second)[i]; } } return false; } }; class MiniDb { private: map<int, pair<int, string>> keyMap; map<pair<int, vector<int>>, vector<int>, Compare> dataMap; public: MiniDb() { } void Create(int tableId, int colNum, const string& keys) { //pair<int, string> p = {colNum, keys}; //keyMap.insert(tableId, p); } void Insert(int tableId, const vector<int>& values) { auto it = keyMap.find(tableId); if (it != keyMap.end()) { vector<int> mark; for (int i = 0; i < ((it->second).second).size(); ++i) { mark.emplace_back(values[((it->second).second)[i] - 'a']); } pair<int, vector<int>> p = {tableId, mark}; dataMap[p] = values; } } vector<vector<int>> Select(int tableId, const vector<string>& conditions) { vector<vector<int>> result; for (auto it = dataMap.begin(); it != dataMap.end(); ++it) { if (it->first.first == tableId) { result.emplace_back(it->second); } } int num = result.size(); for (int i = 0; i < conditions.size(); ++i) { int key = conditions[i] - 'a'; int value = std::stoi(conditions[i].substr(2, conditions[i].size() - 2)); int mark = 0; for (int i = 0; i < num; ++i) { if (result[i][key] == value) { result[mark] == result[i]; mark++; } } num = mark; } vector<vector<int>> resultLast; for (int i = 0; i < num; ++i) { resultLast[i] = result[i]; } return resultLast; } }; 运行时报错main.cpp: In member function 'std::vector<std::vector<int> > MiniDb::Select(int, const std::vector<std::__cxx11::basic_string<char> >&)': main.cpp:75:37: error: no match for 'operator-' (operand types are 'const value_type' {aka 'const std::__cxx11::basic_string<char>'} and 'char') int key = conditions[i] - 'a'; In file included from /usr/include/c++/8/bits/stl_algobase.h:67, from /usr/include/c++/8/bits/char_traits.h:39, from /usr/include/c++/8/ios:40, from main.cpp:6: /usr/include/c++/8/bits/stl_iterator.h:392:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)' operator-(const reverse_iterator<_IteratorL>& __x, ^~~~~~~~ /usr/include/c++/8/bits/stl_iterator.h:392:5: note: template argument deduction/substitution failed: main.cpp:75:39: note: 'const value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>' int key = conditions[i] - 'a'; ^~~ In file included from /usr/include/c++/8/bits/stl_algobase.h:67, from /usr/include/c++/8/bits/char_traits.h:39, from /usr/include/c++/8/ios:40, from main.cpp:6: /usr/include/c++/8/bits/stl_iterator.h:1188:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)' operator-(const move_iterator<_IteratorL>& __x, ^~~~~~~~ /usr/include/c++/8/bits/stl_iterator.h:1188:5: note: template argument deduction/substitution failed: main.cpp:75:39: note: 'const value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>' int key = conditions[i] - 'a'; ^~~ In file included from /usr/include/c++/8/vector:65, from main.cpp:19: /usr/include/c++/8/bits/stl_bvector.h:210:3: note: candidate: 'std::ptrdiff_t std::operator-(const std::_Bit_iterator_base&, const std::_Bit_iterator_base&)' operator-(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y) ^~~~~~~~ /usr/include/c++/8/bits/stl_bvector.h:210:3: note: no known conversion for argument 1 from 'const value_type' {aka 'const std::__cxx11::basic_string<char>'} to 'const std::_Bit_iterator_base&' In file included from /usr/include/c++/8/bits/stl_algobase.h:67, from /usr/include/c++/8/bits/char_traits.h:39, from /usr/include/c++/8/ios:40, from main.cpp:6: /usr/include/c++/8/bits/stl_iterator.h:954:5: note: candidate: 'template<class _IteratorL, class _IteratorR, class _Container> decltype ((__lhs.base() - __rhs.base())) __gnu_cxx::operator-(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)' operator-(const __normal_iterator<_IteratorL, _Container>& __lhs, ^~~~~~~~ /usr/include/c++/8/bits/stl_iterator.h:954:5: note: template argument deduction/substitution failed: main.cpp:75:39: note: 'const value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const __gnu_cxx::__normal_iterator<_IteratorL, _Container>' int key = conditions[i] - 'a'; ^~~ In file included from /usr/include/c++/8/bits/stl_algobase.h:67, from /usr/include/c++/8/bits/char_traits.h:39, from /usr/include/c++/8/ios:40, from main.cpp:6: /usr/include/c++/8/bits/stl_iterator.h:966:5: note: candidate: 'template<class _Iterator, class _Container> typename __gnu_cxx::__normal_iterator<_Iterator, _Container>::difference_type __gnu_cxx::operator-(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)' operator-(const __normal_iterator<_Iterator, _Container>& __lhs, ^~~~~~~~ /usr/include/c++/8/bits/stl_iterator.h:966:5: note: template argument deduction/substitution failed: main.cpp:75:39: note: 'const value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const __gnu_cxx::__normal_iterator<_Iterator, _Container>' int key = conditions[i] - 'a'; ^~~
06-04
### 解决C++编译错误 'no match for operator- (operand types are const std::__cxx11::basic_string<char> and char)' 在C++中，字符串（`std::string`）和字符（`char`）之间的减法运算未被定义。因此，当尝试对...
python反向迭代器_C++ STL 反向迭代器适配器（reverse_iterator）详解
weixin_35373786的博客
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我们知道，C++ 11 的 STL 标准库提供有 4 种迭代器适配器，本节开始将一一介绍它们的功能和用法，这里先讲解反向迭代器适配器。反向迭代器适配器(reverse_iterator)，可简称为反向迭代器或逆向迭代器，常用来对容器进行反向遍历，即从容器中存储的最后一个元素开始，一直遍历到第一个元素。值得一提的是，反向迭代器底层可以选用双向迭代器或者随机访问迭代器作为其基础迭代器。不仅如此，通过对...
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decade777555的博客
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在C++中，可以使用反向迭代器来逆序遍历容器中的元素。反向迭代器是通过rbegin()和rend()方法来获取的，它们分别指向容器的最后一个元素和第一个元素的前一个位置。此类反转双向或随机访问迭代器循环访问范围的方向。原始迭代器（基础迭代器）的副本保留在内部，用于反映在reverse_iterator上执行的操作：每当reverse_iterator递增时，其基本迭代器就会减少，反之亦然。可以随时通过调用成员 base 获取具有当前状态的基迭代器的副本。
C++ STL reverse_iterator反向迭代器适配器(深入了解,一文学会)
木牛的博客
06-07 284
反向迭代器适配器（reverse_iterator），可简称为反向迭代器或逆向迭代器，常用来对容器进行反向遍历，即从容器中存储的最后一个元素开始，一直遍历到第一个元素。值得一提的是，反向迭代器底层可以选用双向迭代器或者随机访问迭代器作为其基础迭代器。不仅如此，通过对 ++（递增）和 --（递减）本文作者原创，转载请附上文章出处与本文链接。
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Defined in header     template class BidirIt > void reverse( BidirIt first, BidirIt last );           Reverses the order of the elements in the range [first, last
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接受一个范围（range），可以直接传递容器或视图，还可以传递一个比较函数。头文件中，是C++20引入的Ranges库的一部分。：接受一个范围（range），可以直接传递容器或视图。头文件中，是C++20引入的Ranges库的一部分。），表示要排序的范围，还可以传递一个比较函数。），表示要反转的范围。
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