我在 boost 变体中有两个结构,变体是 boost::unordered_map 的关键。我正在寻找实现哈希和等于方法的解决方案,该方法将采用变体结构。 下面是一个实现的 RouteHasher 方法(它在运行时不起作用(相同的键参数不会从映射中获取值)。如何实现一个将采用结构的两个成员作为哈希的哈希?
struct v4RouteKey_t
{
uint8 ipv4[4];
uint32 val;
}
struct v6RouteKey_t
{
uint8 ipv6[16];
uint32 val;
}
typedef boost::variant < v4RouteKey_t, v6RouteKey_t > RouteKey;
typedef boost::unordered_map < RouteKey, RouteValue_t > RouteMap;
struct RouteHasher : public boost::static_visitor<std::size_t>
{
template<typename T>
std::size_t operator()(const T& x) const { return boost::hash<T>()(x); }
std::size_t operator()(const RouteKey& x) const { return
boost::apply_visitor(RouteHasher(), x); }
};
struct RouteEquals : public boost::static_visitor<bool>
{
template<typename T>
bool operator()(const T& lhs, const T& rhs) const { return lhs == rhs; }
template<typename T1, typename T2>
bool operator()(const T1& lhs, const T2& rhs) const { return false; }
bool operator()(const RouteKey& lhs, const RouteKey& rhs) const
{ return boost::apply_visitor(RouteEquals(), lhs, rhs); }
};
最佳答案
您是否为 boost::hash_value
实现了哈希(std::hash<>
或 v4RouteKey_t
)和相等性和 v6RouteKey_t
类型?
添加它可以为我编译:
#include <boost/unordered_map.hpp>
#include <boost/variant.hpp>
#include <boost/array.hpp>
#include <boost/tuple/tuple.hpp>
#include <cstdint>
struct v4RouteKey_t {
boost::array<uint8_t, 4> ipv4; uint32_t val;
bool operator==(v4RouteKey_t const& other) const {
return ipv4 == other.ipv4 && val == other.val;
};
};
struct v6RouteKey_t {
boost::array<uint8_t, 16> ipv6; uint32_t val;
bool operator==(v6RouteKey_t const& other) const {
return ipv6 == other.ipv6 && val == other.val;
};
};
size_t hash_value(v4RouteKey_t const& key) { return key.val; }
size_t hash_value(v6RouteKey_t const& key) { return key.val; }
struct RouteValue_t {};
typedef boost::variant<v4RouteKey_t, v6RouteKey_t> RouteKey;
typedef boost::unordered_map<RouteKey, RouteValue_t> RouteMap;
int main() {
RouteMap map;
}
奖金
启用 c++17 的库/编译器可以在没有 boost 的情况下完成所有这些:
#include <unordered_map>
#include <numeric>
#include <variant>
#include <array>
#include <tuple>
struct v4RouteKey_t {
std::array<uint8_t, 4> ipv4; uint32_t val;
bool operator==(v4RouteKey_t const& other) const { return std::tie(ipv4, val) == std::tie(other.ipv4, other.val); };
};
struct v6RouteKey_t {
std::array<uint8_t, 16> ipv6; uint32_t val;
bool operator==(v6RouteKey_t const& other) const { return std::tie(ipv6, val) == std::tie(other.ipv6, other.val); };
};
namespace std {
template <> struct hash<v4RouteKey_t> {
size_t operator()(v4RouteKey_t const& key) {
return std::accumulate(key.ipv4.begin(), key.ipv4.end(), size_t(key.val), [](size_t seed, uint8_t b) { return (seed*139) ^ b; });
}
};
template <> struct hash<v6RouteKey_t> {
size_t operator()(v6RouteKey_t const& key) {
return std::accumulate(key.ipv6.begin(), key.ipv6.end(), size_t(key.val), [](size_t seed, uint8_t b) { return (seed*139) ^ b; });
}
};
}
struct RouteValue_t {};
typedef std::variant<v4RouteKey_t, v6RouteKey_t> RouteKey;
typedef std::unordered_map<RouteKey, RouteValue_t> RouteMap;
int main() {
RouteMap map;
}
关于c++ - 以结构作为 boost::unordered_map 中的键的 boost 变体,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46683847/