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 <string>
#include <iostream>
#include <unordered_set>
#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) {
}
string firstname() const {
return fname;
};
string lastname() const {
return lname;
};
long number() const {
return no;
};
friend ostream& operator << (ostream& strm, const Customer& c) {
return strm << "[" << c.fname << "," << c.lname << ","
<< c.no << "]";
}
};
int main()
{
// lambda for user-defined hash function
auto hash = [] (const Customer& c) {
return hash_val(c.firstname(),c.lastname(),c.number());
};
// lambda for user-defined equality criterion
auto eq = [] (const Customer& c1, const Customer& c2) {
return c1.number() == c2.number();
};
// create unordered set with user-defined behavior
unordered_set<Customer,
decltype(hash),decltype(eq)> custset(10,hash,eq);
custset.insert(Customer("nico","josuttis",42));
PRINT_ELEMENTS(custset);
}