The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <unordered_set>
#include <string>
#include <iostream>
#include "hashval.hpp"
#include "print.hpp"
using namespace std;
class Customer {
private:
string fname;
string lname;
long no;
public:
Customer (const string& fn, const string& ln, long n)
: fname(fn), lname(ln), no(n) {}
friend ostream& operator << (ostream& strm, const Customer& c) {
return strm << "[" << c.fname << "," << c.lname << ","
<< c.no << "]";
}
friend class CustomerHash;
friend class CustomerEqual;
};
class CustomerHash
{
public:
std::size_t operator() (const Customer& c) const {
return hash_val(c.fname,c.lname,c.no);
}
};
class CustomerEqual
{
public:
bool operator() (const Customer& c1, const Customer& c2) const {
return c1.no == c2.no;
}
};
int main()
{
// unordered set with own hash function and equivalence criterion
unordered_set<Customer,CustomerHash,CustomerEqual> custset;
custset.insert(Customer("nico","josuttis",42));
PRINT_ELEMENTS(custset);
}