How to have a tuple as both the key and value of an unordered map using a hash function or boost? - boost

Question

I am trying to use a tuple<string, string, string> that will be placed as both the key and value of the unordered map as such:
unordered_map < tuple<string, string, string>, tuple<string, string, string>, hash_tuple> songInfo;
I understand I'm supposed to define a hash function because C++ does not have a hasher for std::tuple. However, I'm struggling to implement this through the explanations I've been reading on the other stack overflow posts. This is what my code has so far:
#include <iostream>
#include <unordered_map>
#include <vector>
#include <fstream>
#include <tuple>
using namespace std;
typedef std::tuple<string, string, string> t;
struct hash_tuple : public unary_function <t, size_t> {
size_t operator()(const t& x) const
{
return get<0>(x) ^ get<1>(x) ^ get<2>(x);
}
};
typedef unordered_map <t, t, hash_tuple> songInfo;
int main() {
string filePath = "../data/songInfo.txt";
fstream songFile;
songFile.open("songInfo.txt");
string line;
string name, artist, date, duration, genre, mood;
vector <string> store;
while (getline(songFile, line, ',')) {
store.push_back(line);
tuple <string, string, string> iD(store[0], store[1], store[2]);
tuple <string, string, string> info(store[3], store[4], store[5]);
songInfo[iD] = info;
}
for (auto it = songInfo.begin(); it != songInfo.end(); it++)
cout << "[" << get<0>(it->first) << ", " << get<1>(it->first) << ", " <<
get<2>(it->first) << "] ==>" << get<0>(it->second) << ", " << get<1>(it-
>second) << ", " << get<2>(it->second) << endl;
}

Answer 1

Okay "fixing" the problem is easy: you wanted to XOR-combine hashes, not strings:
struct hash_tuple {
size_t operator()(const t& x) const {
std::hash<std::string> h{};
return h(get<0>(x)) ^ h(get<1>(x)) ^ h(get<2>(x));
}
};
Note that using namespace std is frowned upon, using declarations trump typedefs and unary_function<> is deprecated. Next up there were some syntax errors.
Combining fixes for these: Live On Coliru
#include <fstream>
#include <iostream>
#include <tuple>
#include <unordered_map>
#include <vector>
using t = std::tuple<std::string, std::string, std::string>;
struct hash_tuple {
size_t operator()(const t& x) const {
std::hash<std::string> h{};
return h(get<0>(x)) ^ h(get<1>(x)) ^ h(get<2>(x));
}
};
using SongInfo = std::unordered_map<t, t, hash_tuple>;
int main() {
std::string filePath = "songInfo.txt";
std::fstream songFile;
songFile.open("songInfo.txt");
std::string line;
std::string name, artist, date, duration, genre, mood;
std::vector<std::string> store;
SongInfo songInfo;
while (getline(songFile, line, ',')) {
store.push_back(line);
std::tuple<std::string, std::string, std::string> iD(store[0], store[1], store[2]);
std::tuple<std::string, std::string, std::string> info(store[3], store[4], store[5]);
songInfo[iD] = info;
}
for (auto it = songInfo.begin(); it != songInfo.end(); it++)
std::cout << "[" << get<0>(it->first) << ", " << get<1>(it->first)
<< ", " << get<2>(it->first) << "] ==>" << get<0>(it->second)
<< ", " << get<1>(it->second) << ", " << get<2>(it->second)
<< std::endl;
}