我正在尝试在我的应用程序中构建链表的列表。该列表将包含唯一的IP地址，并且对于每个IP地址，我都有一个应用程序列表。我正在尝试使用unordered_map构建它，将Boost :: boost :: asio :: ip :: address作为键，将std :: list作为值：
#include <boost/unordered/unordered_map.hpp>
#include <iostream>
#include <list>
using namespace boost::asio::ip;
using namespace std;
typedef int ApplicationID;
typedef address IPAddress;
typedef list <ApplicationID> APP_LIST;
typedef boost::unordered::unordered_map <IPAddress, APP_LIST> USER_MAP;
USER_MAP user_map;
稍后我尝试获取与IP地址关联的列表，如下所示：
APP_LIST *list = &user_map[ip];
但是我在编辑中遇到错误，所以请你指出问题是什么？
是否可以使用Boost：IPaddress作为关键功能？
另一个问题是可以使用char [some_size]作为键值吗？
错误输出：
In file included from /boost/functional/hash/hash.hpp:535:0,
from /boost/functional/hash.hpp:6,
from /boost/unordered/unordered_map.hpp:21,
from ipc_module.cpp:18:
/boost/functional/hash/extensions.hpp: In member function ‘std::size_t boost::hash<T>::operator()(const T&) const [with T = boost::asio::ip::address, std::size_t = long unsigned int]’:
/boost/unordered/detail/unique.hpp:331:55: instantiated from ‘boost::unordered::detail::table_impl<Types>::value_type& boost::unordered::detail::table_impl<Types>::operator[](const key_type&) [with Types = boost::unordered::detail::map<std::allocator<std::pair<const boost::asio::ip::address, std::list<int> > >, boost::asio::ip::address, std::list<int>, boost::hash<boost::asio::ip::address>, std::equal_to<boost::asio::ip::address> >, boost::unordered::detail::table_impl<Types>::value_type = std::pair<const boost::asio::ip::address, std::list<int> >, boost::unordered::detail::table_impl<Types>::key_type = boost::asio::ip::address]’
/boost/unordered/unordered_map.hpp:1192:26: instantiated from ‘boost::unordered::unordered_map<K, T, H, P, A>::mapped_type& boost::unordered::unordered_map<K, T, H, P, A>::operator[](const key_type&) [with K = boost::asio::ip::address, T = std::list<int>, H = boost::hash<boost::asio::ip::address>, P = std::equal_to<boost::asio::ip::address>, A = std::allocator<std::pair<const boost::asio::ip::address, std::list<int> > >, boost::unordered::unordered_map<K, T, H, P, A>::mapped_type = std::list<int>, boost::unordered::unordered_map<K, T, H, P, A>::key_type = boost::asio::ip::address]’
ipc_module.cpp:175:40: instantiated from here
/boost/functional/hash/extensions.hpp:176:34: error: no matching function for call to ‘hash_value(const boost::asio::ip::address&)’
/boost/functional/hash/extensions.hpp:176:34: note: candidates are:
/boost/smart_ptr/shared_ptr.hpp:708:33: note: template<class T> std::size_t boost::hash_value(const boost::shared_ptr<T>&)
/boost/functional/hash/hash.hpp:144:24: note: std::size_t boost::hash_value(bool)
/boost/functional/hash/hash.hpp:144:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘bool’
/boost/functional/hash/hash.hpp:149:24: note: std::size_t boost::hash_value(char)
/boost/functional/hash/hash.hpp:149:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘char’
/boost/functional/hash/hash.hpp:154:24: note: std::size_t boost::hash_value(unsigned char)
/boost/functional/hash/hash.hpp:154:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘unsigned char’
/boost/functional/hash/hash.hpp:159:24: note: std::size_t boost::hash_value(signed char)
/boost/functional/hash/hash.hpp:159:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘signed char’
/boost/functional/hash/hash.hpp:164:24: note: std::size_t boost::hash_value(short int)
/boost/functional/hash/hash.hpp:164:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘short int’
/boost/functional/hash/hash.hpp:169:24: note: std::size_t boost::hash_value(short unsigned int)
/boost/functional/hash/hash.hpp:169:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘short unsigned int’
/boost/functional/hash/hash.hpp:174:24: note: std::size_t boost::hash_value(int)
/boost/functional/hash/hash.hpp:174:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘int’
/boost/functional/hash/hash.hpp:179:24: note: std::size_t boost::hash_value(unsigned int)
/boost/functional/hash/hash.hpp:179:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘unsigned int’
/boost/functional/hash/hash.hpp:184:24: note: std::size_t boost::hash_value(long int)
/boost/functional/hash/hash.hpp:184:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘long int’
/boost/functional/hash/hash.hpp:189:24: note: std::size_t boost::hash_value(long unsigned int)
/boost/functional/hash/hash.hpp:189:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘long unsigned int’
/boost/functional/hash/hash.hpp:195:24: note: std::size_t boost::hash_value(wchar_t)
/boost/functional/hash/hash.hpp:195:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘wchar_t’
/boost/functional/hash/hash.hpp:202:24: note: std::size_t boost::hash_value(boost::long_long_type)
/boost/functional/hash/hash.hpp:202:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘boost::long_long_type {aka long long int}’
/boost/functional/hash/hash.hpp:207:24: note: std::size_t boost::hash_value(boost::ulong_long_type)
/boost/functional/hash/hash.hpp:207:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘boost::ulong_long_type {aka long long unsigned int}’
/boost/functional/hash/hash.hpp:215:36: note: template<class T> std::size_t boost::hash_value(T* const&)
/boost/functional/hash/hash.hpp:308:24: note: template<class T, unsigned int N> std::size_t boost::hash_value(const T (&)[N])
/boost/functional/hash/hash.hpp:314:24: note: template<class T, unsigned int N> std::size_t boost::hash_value(T (&)[N])
/boost/functional/hash/hash.hpp:327:24: note: std::size_t boost::hash_value(float)
/boost/functional/hash/hash.hpp:327:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘float’
/boost/functional/hash/hash.hpp:332:24: note: std::size_t boost::hash_value(double)
/boost/functional/hash/hash.hpp:332:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘double’
/boost/functional/hash/hash.hpp:337:24: note: std::size_t boost::hash_value(long double)
/boost/functional/hash/hash.hpp:337:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘long double’
/boost/functional/hash/hash.hpp:321:24: note: template<class Ch, class A> std::size_t boost::hash_value(const std::basic_string<Ch, std::char_traits<_CharT>, A>&)
/boost/functional/hash/hash.hpp:343:24: note: std::size_t boost::hash_value(std::type_index)
/boost/functional/hash/hash.hpp:343:24: note: no known conversion for argument 1 from ‘const boost::asio::ip::address’ to ‘std::type_index’
/boost/functional/hash/extensions.hpp:54:17: note: template<class A, class B> std::size_t boost::hash_value(const std::pair<_T1, _T2>&)
/boost/functional/hash/extensions.hpp:63:17: note: template<class T, class A> std::size_t boost::hash_value(const std::vector<_Tp, _Alloc>&)
/boost/functional/hash/extensions.hpp:69:17: note: template<class T, class A> std::size_t boost::hash_value(const std::list<_Tp, _Alloc>&)
/boost/functional/hash/extensions.hpp:75:17: note: template<class T, class A> std::size_t boost::hash_value(const std::deque<_Tp, _Alloc>&)
/boost/functional/hash/extensions.hpp:81:17: note: template<class K, class C, class A> std::size_t boost::hash_value(const std::set<_Key, _Compare, _Alloc>&)
/boost/functional/hash/extensions.hpp:87:17: note: template<class K, class C, class A> std::size_t boost::hash_value(const std::multiset<_Key, _Compare, _Alloc>&)
/boost/functional/hash/extensions.hpp:93:17: note: template<class K, class T, class C, class A> std::size_t boost::hash_value(const std::map<_Key, _Tp, _Compare, _Alloc>&)
/boost/functional/hash/extensions.hpp:99:17: note: template<class K, class T, class C, class A> std::size_t boost::hash_value(const std::multimap<_Key, _Tp, _Compare, _Alloc>&)
/boost/functional/hash/extensions.hpp:105:17: note: template<class T> std::size_t boost::hash_value(const std::complex<_Tp>&)
/boost/functional/hash/extensions.hpp:177:9: warning: control reaches end of non-void function [-Wreturn-type]
/boost/asio/error.hpp: At global scope:
/boost/asio/error.hpp:244:45: warning: ‘boost::asio::error::system_category’ defined but not used [-Wunused-variable]
/boost/asio/error.hpp:246:45: warning: ‘boost::asio::error::netdb_category’ defined but not used [-Wunused-variable]
/boost/asio/error.hpp:248:45: warning: ‘boost::asio::error::addrinfo_category’ defined but not used [-Wunused-variable]
/boost/asio/error.hpp:250:45: warning: ‘boost::asio::error::misc_category’ defined but not used [-Wunused-variable]
答案 0 :(得分：5)
这是我在简要检查ip::address的类接口后想出的内容。
我想指出，使用起来非常浪费。特别是如果您碰巧知道所有地址都是ipv4，例如我更喜欢按ulong键入。
namespace boost
{
template <>
struct hash<IPAddress>
{
size_t operator()(IPAddress const& v) const {
if (v.is_v4())
return v.to_v4().to_ulong();
if (v.is_v6())
{
auto const& range = v.to_v6().to_bytes();
return hash_range(range.begin(), range.end());
}
if (v.is_unspecified())
{
// guaranteed to be random: chosen by fair dice roll
return static_cast<size_t>(0x4751301174351161ul);
}
return hash_value(v.to_string());
}
};
}
查看 Live on Coliru ：
#include <boost/asio.hpp>
#include <boost/unordered/unordered_map.hpp>
#include <iostream>
#include <list>
typedef int ApplicationID;
typedef boost::asio::ip::address IPAddress;
typedef std::list<ApplicationID> APP_LIST;
typedef boost::unordered::unordered_map<IPAddress, APP_LIST> USER_MAP;
namespace boost
{
template <>
struct hash<IPAddress>
{
size_t operator()(IPAddress const& v) const {
if (v.is_v4())
return v.to_v4().to_ulong();
if (v.is_v6())
{
auto const& range = v.to_v6().to_bytes();
return hash_range(range.begin(), range.end());
}
if (v.is_unspecified())
return 0x4751301174351161ul;
return hash_value(v.to_string());
}
};
}
int main()
{
USER_MAP map;
map.insert({ {}, {} });
}
答案 1 :(得分：2)
如果为IPaddress编写哈希函数，它将起作用。
答案 2 :(得分：2)
这是一个古老的问题，但是我最近在用c ++ 17编写游戏时遇到了同样的问题。
这是我解决的方法：
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