how to insert into an unordered_map for a given struct
Hi,
I have this code which gives me an illegal indirection:
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unordered_map<Record, Record, RHash> rmap;
rmap.insert(Record{ "juan"s, 55 }, Record{ "leslie"s, 40 });
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where Record is defined like this:
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struct Record
{
string name;
int product_code;
friend bool operator==(const Record& lhs, const Record& rhs)
{
return lhs.name == rhs.name
&& lhs.product_code == rhs.product_code;
}
}
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and RHash like this:
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struct RHash
{
size_t operator()(const Record& r) const
{
return hash<string>()(r.name) ^ hash<int>()(r.product_code);
}
};
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What am I doing wrong??
Thank you in advance... first time dealing with an unordered_map!!
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#include <iostream>
#include <string>
#include <unordered_map>
struct Record
{
std::string name;
int product_code;
friend auto operator<=> ( const Record&, const Record& ) noexcept = default ;
struct hash
{
size_t operator()(const Record& r) const noexcept
{ return std::hash<std::string>()(r.name) ^ std::hash<int>()(r.product_code) ; }
};
};
int main()
{
std::unordered_map< Record, Record, Record::hash > rmap ;
// note: the value_type is std::pair
const bool ok = rmap.insert( /* std::pair */{ Record{ "abc", 1 }, Record{ "def", 2 } } ).second ;
if(ok) std::cout << "ok\n" ;
}
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You can also use .emplace()
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int main()
{
std::unordered_map< Record, Record, Record::hash > rmap ;
const bool ok = rmap.emplace( Record{ "abc", 1 }, Record{ "def", 2 } ).second ;
if(ok) std::cout << "ok\n" ;
}
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You can also use c++20 std::piecewise_construct:
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int main()
{
std::unordered_map< Record, Record, Record::hash > rmap ;
const bool ok = rmap.emplace(
std::piecewise_construct,
std::forward_as_tuple("abc", 1),
std::forward_as_tuple("def", 2)).second;
if(ok) std::cout << "ok\n" ;
}
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Last edited on
Thanks!!
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