使用结构作为键和值创建 std::map [英] Creating std::map with a structure as its key and value
本文介绍了使用结构作为键和值创建 std::map的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我想在一个类中定义一个静态映射，它将具有一个结构作为它的键和值.我读过一个 '<'需要定义运算符，因此我已将该定义包含在结构本身中(我随机定义了它，因为我不需要在程序中的任何地方进行任何比较).
I want to define a static map inside a class, which will have a structure as both it's key and value. I've read that a '<' operator is needed to be defined, therefore I've included that definition inside the struct itself(I've randomly defined it as I don't need any comparison anywhere in my program).
下面的示例代码无法编译.编译器产生了很多我现在不明白的警告和错误.(请忽略主函数中未初始化的值):
The below sample code doesn't compile.The compiler produces a lot of warnings and errors which I don't understand right now. (Please ignore the uninitialized values in the main function):
#include<string>
#include<iostream>
#include<map>
using namespace std;
struct RJNodeAddress
{
string m_ip;
string m_port;
bool operator<(const RJNodeAddress &l)
{
int l_size=l.m_ip.size();
int r_size=l.m_port.size();
return (l_size < r_size);
}
};
struct RJNodeDetails
{
string m_NodeType;
int m_appId;
};
class RJWebsocket
{
public:
static map<RJNodeAddress,RJNodeDetails> m_Nodes;
};
int main()
{
RJNodeAddress l_node;
RJNodeDetails l_nodeDetails = RJWebsocket::m_Nodes[l_node];
}
编译器输出
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h: In instantiation of âconstexpr bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = RJNodeAddress]â:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_map.h:491:32: required from âstd::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = RJNodeAddress; _Tp = RJNodeDetails; _Compare = std::less<RJNodeAddress>; _Alloc = std::allocator<std::pair<const RJNodeAddress, RJNodeDetails> >; std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = RJNodeDetails; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = RJNodeAddress]â
test.cpp:34:59: required from here
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: error: no match for âoperator<â (operand types are âconst RJNodeAddressâ and âconst RJNodeAddressâ)
{ return __x < __y; }
~~~~^~~~~
test.cpp:10:14: note: candidate: bool RJNodeAddress::operator<(const RJNodeAddress&) <near match>
bool operator<(const RJNodeAddress &l)
^~~~~~~~
test.cpp:10:14: note: passing âconst RJNodeAddress*â as âthisâ argument discards qualifiers
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_algobase.h:64:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/char_traits.h:39,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:40,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_pair.h:449:5: 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)
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_pair.h:449:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::pair<_T1, _T2>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_algobase.h:67:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/char_traits.h:39,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:40,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:305:5: note: candidate: template<class _Iterator> constexpr bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
operator<(const reverse_iterator<_Iterator>& __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:305:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::reverse_iterator<_Iterator>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_algobase.h:67:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/char_traits.h:39,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:40,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:343:5: note: candidate: template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
operator<(const reverse_iterator<_IteratorL>& __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:343:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::reverse_iterator<_Iterator>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_algobase.h:67:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/char_traits.h:39,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:40,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:1142:5: note: candidate: template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)
operator<(const move_iterator<_IteratorL>& __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:1142:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::move_iterator<_IteratorL>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_algobase.h:67:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/char_traits.h:39,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:40,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:1148:5: note: candidate: template<class _Iterator> constexpr bool std::operator<(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)
operator<(const move_iterator<_Iterator>& __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_iterator.h:1148:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::move_iterator<_IteratorL>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:48:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:52,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/string_view:485:5: note: candidate: template<class _CharT, class _Traits> bool std::operator<(std::basic_string_view<_CharT, _Traits>, std::basic_string_view<_CharT, _Traits>)
operator< (basic_string_view<_CharT, _Traits> __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/string_view:485:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âRJNodeAddressâ is not derived from âstd::basic_string_view<_CharT, _Traits>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:48:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:52,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/string_view:491:5: note: candidate: template<class _CharT, class _Traits> bool std::operator<(std::basic_string_view<_CharT, _Traits>, std::__detail::__idt<std::basic_string_view<_CharT, _Traits> >)
operator< (basic_string_view<_CharT, _Traits> __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/string_view:491:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âRJNodeAddressâ is not derived from âstd::basic_string_view<_CharT, _Traits>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:48:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:52,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/string_view:497:5: note: candidate: template<class _CharT, class _Traits> bool std::operator<(std::__detail::__idt<std::basic_string_view<_CharT, _Traits> >, std::basic_string_view<_CharT, _Traits>)
operator< (__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/string_view:497:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âRJNodeAddressâ is not derived from âstd::basic_string_view<_CharT, _Traits>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:52:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:5892:5: note: candidate: 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,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:5892:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::basic_string<_CharT, _Traits, _Alloc>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:52:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:5905:5: note: candidate: 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,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:5905:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::basic_string<_CharT, _Traits, _Alloc>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:52:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:5917:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
operator<(const _CharT* __lhs,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/basic_string.h:5917:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: mismatched types âconst _CharT*â and âRJNodeAddressâ
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/ios_base.h:46:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/ios:42,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/ostream:38,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/iostream:39,
from test.cpp:2:
/opt/rh/devtoolset-7/root/usr/include/c++/7/system_error:208:3: note: candidate: bool std::operator<(const std::error_code&, const std::error_code&)
operator<(const error_code& __lhs, const error_code& __rhs) noexcept
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/system_error:208:3: note: no known conversion for argument 1 from âconst RJNodeAddressâ to âconst std::error_code&â
/opt/rh/devtoolset-7/root/usr/include/c++/7/system_error:282:3: note: candidate: bool std::operator<(const std::error_condition&, const std::error_condition&)
operator<(const error_condition& __lhs,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/system_error:282:3: note: no known conversion for argument 1 from âconst RJNodeAddressâ to âconst std::error_condition&â
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:39:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:808:5: note: candidate: template<class _Tp, class _Up> constexpr std::__optional_relop_t<decltype ((declval<_Tp>() < declval<_Up>()))> std::operator<(const std::optional<_Tp>&, const std::optional<_Up>&)
operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:808:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::optional<_Tp>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:39:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:861:5: note: candidate: template<class _Tp> constexpr bool std::operator<(const std::optional<_Tp>&, std::nullopt_t)
operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:861:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::optional<_Tp>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:39:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:866:5: note: candidate: template<class _Tp> constexpr bool std::operator<(std::nullopt_t, const std::optional<_Tp>&)
operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:866:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::optional<_Tp>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:39:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:926:5: note: candidate: template<class _Tp, class _Up> constexpr std::__optional_relop_t<decltype ((declval<_Tp>() < declval<_Up>()))> std::operator<(const std::optional<_Tp>&, const _Up&)
operator<(const optional<_Tp>& __lhs, const _Up& __rhs)
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:926:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::optional<_Tp>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:39:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:932:5: note: candidate: template<class _Tp, class _Up> constexpr std::__optional_relop_t<decltype ((declval<_Up>() < declval<_Tp>()))> std::operator<(const _Up&, const std::optional<_Tp>&)
operator<(const _Up& __lhs, const optional<_Tp>& __rhs)
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/optional:932:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::optional<_Tp>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/tuple:39:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:40,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/array:262:5: note: candidate: template<class _Tp, long 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)
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/array:262:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::array<_Tp, _Nm>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/node_handle.h:40:0,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:72,
from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/tuple:1410:5: note: candidate: template<class ... _TElements, class ... _UElements> constexpr bool std::operator<(const std::tuple<_Tps ...>&, const std::tuple<_Elements ...>&)
operator<(const tuple<_TElements...>& __t,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/tuple:1410:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::tuple<_Tps ...>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:60:0,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:1543:5: 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,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_tree.h:1543:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:61:0,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_map.h:1397:5: 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,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_map.h:1397:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::map<_Key, _Tp, _Compare, _Alloc>â
{ return __x < __y; }
~~~~^~~~~
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/map:62:0,
from test.cpp:3:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_multimap.h:1062:5: 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,
^~~~~~~~
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_multimap.h:1062:5: note: template argument deduction/substitution failed:
In file included from /opt/rh/devtoolset-7/root/usr/include/c++/7/string:48:0,
from test.cpp:1:
/opt/rh/devtoolset-7/root/usr/include/c++/7/bits/stl_function.h:386:20: note: âconst RJNodeAddressâ is not derived from âconst std::multimap<_Key, _Tp, _Compare, _Alloc>â
{ return __x < __y; }
~~~~^~~~~
推荐答案
因为 std::map 中的键是 const 你的 operator< 方法也必须是 const :
As keys in std::map are const your operator< method must be const as well:
bool operator<(const RJNodeAddress &l) const
// ^ here
无论如何它都应该是常量，因为它不会修改对象，但在这种情况下，缺少它会导致编译错误.
it should be const anyway as it does not modify the object but in this case missing it leads to compilation errors.
这篇关于使用结构作为键和值创建 std::map的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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