使用自定义比较器声明 C++ 优先级队列的问题
Issues with Declaring a C++ Priority Queue using a custom Comparator
我一直在尝试实现一个由自定义数据类型和自定义比较器组成的优先级队列，但是当我尝试编译时出现此错误。我尝试了多个声明，但它们都产生了这个错误。
priority_queue<myData, vector<myData>, myComp> myPQ;
priority_queue<myData, vector<myData>, myComp> myPQ(compVariable);
我也在尝试创建这些优先级队列的向量。
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h: In instantiation of ‘bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = Order]’:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_heap.h:183:47: required from ‘void std::__push_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Order*, std::vector<Order, std::allocator<Order> > >; _Distance = long int; _Tp = Order; _Compare = std::less<Order>]’
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_heap.h:222:58: required from ‘void std::push_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Order*, std::vector<Order, std::allocator<Order> > >; _Compare = std::less<Order>]’
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_queue.h:499:41: required from ‘void std::priority_queue<_Tp, _Sequence, _Compare>::push(const value_type&) [with _Tp = Order; _Sequence = std::vector<Order, std::allocator<Order> >; _Compare = std::less<Order>; std::priority_queue<_Tp, _Sequence, _Compare>::value_type = Order]’
Market.cpp:144:32: required from here
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: error: no match for ‘operator<’ (operand types are ‘const Order’ and ‘const Order’)
{ return __x < __y; }
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: candidates are:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_pair.h:220:5: note: 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)
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_pair.h:220:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::pair<_T1, _T2>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:297:5: note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
operator<(const reverse_iterator<_Iterator>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:297:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::reverse_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:347:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
operator<(const reverse_iterator<_IteratorL>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:347:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::reverse_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1055:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_IteratorR>&)
operator<(const move_iterator<_IteratorL>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1055:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::move_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1061:5: note: template<class _Iterator> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&)
operator<(const move_iterator<_Iterator>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1061:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::move_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:52:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2569:5: 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>&)
operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2569:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:52:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2581:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2581:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:52:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2593:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
operator<(const _CharT* __lhs,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2593:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: mismatched types ‘const _CharT*’ and ‘Order’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/vector:64:0,
from P2.h:4,
from Market.cpp:3:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_vector.h:1420:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_vector.h:1420:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::vector<_Tp, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/deque:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:60,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:273:5: 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>&)
operator<(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:273:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::_Deque_iterator<_Tp, _Ref, _Ptr>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/deque:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:60,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:281:5: note: template<class _Tp, class _RefL, class _PtrL, class _RefR, class _PtrR> bool std::operator<(const std::_Deque_iterator<_Tp, _Ref, _Ptr>&, const std::_Deque_iterator<_Tp, _RefR, _PtrR>&)
operator<(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:281:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::_Deque_iterator<_Tp, _Ref, _Ptr>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/deque:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:60,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:1975:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::deque<_Tp, _Alloc>&, const std::deque<_Tp, _Alloc>&)
operator<(const deque<_Tp, _Alloc>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:1975:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::deque<_Tp, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:64:0,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_queue.h:286:5: note: template<class _Tp, class _Seq> bool std::operator<(const std::queue<_Tp, _Seq>&, const std::queue<_Tp, _Seq>&)
operator<(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_queue.h:286:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::queue<_Tp, _Seq>’
{ return __x < __y; }
这是导致错误的示例：
class myData {
public:
int a;
int b;
int c;
int d;
};
class myComp {
public:
bool operator()(myData& d1, myData& d2) {
if(d1.a == d2.a) {
return d2.b < d2.c;
}
else {
return d1.a < d2.a;
}
}
};
priority_queue<myData, vector<myData>, myComp> myPQ;
vector<priority_queue<myData, vector<myData>, myComp> > vec_PQ(n, myPQ);
发件人：http://en.cppreference.com/w/cpp/concept/Compare
The concept Compare is a set of requirements expected by some of the standard library facilities from the user-provided function object types.
The return value of the function call operation applied to an object of type Compare, when contextually converted to bool, yields true if the first argument of the call appears before the second in the strict weak ordering relation induced by this Compare type, and false otherwise.
As with any BinaryPredicate, evaluation of that expression is not allowed to call non-const member functions of the dereferenced iterators.
myComp::operator() 的参数应该是 const&。
bool myComp::operator()(myData const& d1, myData const& d2) {
如@T.C所示。在注释中，函数本身应该是一个 const 成员函数，但在这种情况下完全没有必要。
我一直在尝试实现一个由自定义数据类型和自定义比较器组成的优先级队列，但是当我尝试编译时出现此错误。我尝试了多个声明，但它们都产生了这个错误。
priority_queue<myData, vector<myData>, myComp> myPQ;
priority_queue<myData, vector<myData>, myComp> myPQ(compVariable);
我也在尝试创建这些优先级队列的向量。
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h: In instantiation of ‘bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = Order]’:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_heap.h:183:47: required from ‘void std::__push_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Order*, std::vector<Order, std::allocator<Order> > >; _Distance = long int; _Tp = Order; _Compare = std::less<Order>]’
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_heap.h:222:58: required from ‘void std::push_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Order*, std::vector<Order, std::allocator<Order> > >; _Compare = std::less<Order>]’
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_queue.h:499:41: required from ‘void std::priority_queue<_Tp, _Sequence, _Compare>::push(const value_type&) [with _Tp = Order; _Sequence = std::vector<Order, std::allocator<Order> >; _Compare = std::less<Order>; std::priority_queue<_Tp, _Sequence, _Compare>::value_type = Order]’
Market.cpp:144:32: required from here
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: error: no match for ‘operator<’ (operand types are ‘const Order’ and ‘const Order’)
{ return __x < __y; }
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: candidates are:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_pair.h:220:5: note: 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)
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_pair.h:220:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::pair<_T1, _T2>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:297:5: note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
operator<(const reverse_iterator<_Iterator>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:297:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::reverse_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:347:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
operator<(const reverse_iterator<_IteratorL>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:347:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::reverse_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1055:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_IteratorR>&)
operator<(const move_iterator<_IteratorL>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1055:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::move_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_algobase.h:67:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1061:5: note: template<class _Iterator> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&)
operator<(const move_iterator<_Iterator>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_iterator.h:1061:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::move_iterator<_Iterator>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:52:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2569:5: 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>&)
operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2569:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:52:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2581:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2581:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:52:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2593:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
operator<(const _CharT* __lhs,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/basic_string.h:2593:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: mismatched types ‘const _CharT*’ and ‘Order’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/vector:64:0,
from P2.h:4,
from Market.cpp:3:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_vector.h:1420:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_vector.h:1420:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::vector<_Tp, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/deque:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:60,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:273:5: 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>&)
operator<(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:273:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::_Deque_iterator<_Tp, _Ref, _Ptr>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/deque:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:60,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:281:5: note: template<class _Tp, class _RefL, class _PtrL, class _RefR, class _PtrR> bool std::operator<(const std::_Deque_iterator<_Tp, _Ref, _Ptr>&, const std::_Deque_iterator<_Tp, _RefR, _PtrR>&)
operator<(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:281:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::_Deque_iterator<_Tp, _Ref, _Ptr>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/deque:64:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:60,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:1975:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::deque<_Tp, _Alloc>&, const std::deque<_Tp, _Alloc>&)
operator<(const deque<_Tp, _Alloc>& __x,
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_deque.h:1975:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::deque<_Tp, _Alloc>’
{ return __x < __y; }
^
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/queue:64:0,
from Market.cpp:6:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_queue.h:286:5: note: template<class _Tp, class _Seq> bool std::operator<(const std::queue<_Tp, _Seq>&, const std::queue<_Tp, _Seq>&)
operator<(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
^
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_queue.h:286:5: note: template argument deduction/substitution failed:
In file included from /usr/um/gcc-4.8.2/include/c++/4.8.2/string:48:0,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/locale_classes.h:40,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/bits/ios_base.h:41,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ios:42,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/ostream:38,
from /usr/um/gcc-4.8.2/include/c++/4.8.2/iostream:39,
from Market.cpp:1:
/usr/um/gcc-4.8.2/include/c++/4.8.2/bits/stl_function.h:235:20: note: ‘const Order’ is not derived from ‘const std::queue<_Tp, _Seq>’
{ return __x < __y; }
这是导致错误的示例：
class myData {
public:
int a;
int b;
int c;
int d;
};
class myComp {
public:
bool operator()(myData& d1, myData& d2) {
if(d1.a == d2.a) {
return d2.b < d2.c;
}
else {
return d1.a < d2.a;
}
}
};
priority_queue<myData, vector<myData>, myComp> myPQ;
vector<priority_queue<myData, vector<myData>, myComp> > vec_PQ(n, myPQ);
发件人：http://en.cppreference.com/w/cpp/concept/Compare
The concept Compare is a set of requirements expected by some of the standard library facilities from the user-provided function object types.
The return value of the function call operation applied to an object of type Compare, when contextually converted to
bool, yieldstrueif the first argument of the call appears before the second in the strict weak ordering relation induced by this Compare type, andfalseotherwise.As with any BinaryPredicate, evaluation of that expression is not allowed to call non-const member functions of the dereferenced iterators.
myComp::operator() 的参数应该是 const&。
bool myComp::operator()(myData const& d1, myData const& d2) {
如@T.C所示。在注释中，函数本身应该是一个 const 成员函数，但在这种情况下完全没有必要。