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Source Code
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#include<iostream>
#include<map>
#include<unordered_map>
struct CityRecord
{
std::string Name;
uint64_t Population;
double Latitude, Longtitude;
//friend declaration for operator==
};
//implement operator==
bool operator==(const CityRecord &lhs, const CityRecord &rhs)
{
return (lhs.Name == rhs.Name) && (lhs.Population == rhs.Population) && (lhs.Latitude ==rhs.Latitude) && (lhs.Longtitude == rhs.Longtitude);
}
namespace std {
template<>
struct hash<CityRecord>
{
//-----------------------------------------------vvvvv-->added this const
size_t operator()(const CityRecord& key) const
{
return hash<std::string>()(key.Name) ^ hash<uint64_t>()(key.Population) ^ hash<double>()(key.Latitude) ^ hash<double>()(key.Longtitude);
}
};
}
int main()
{
std::unordered_map<CityRecord, uint32_t> foundedMap;
foundedMap[CityRecord{ "London", 500000, 2.4, 9.4 }] = 1850;
uint32_t NewYorkYear = foundedMap[CityRecord{ "NY", 7000000, 2.4, 9.4 }];
}
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