STL - Unorderedset - 自定义哈希函数

1. hash工具类

hashval.hpp

#ifndef _Core_HashVal_H_
#define _Core_HashVal_H_

#include <functional>

// from boost (functional/hash):
// see http://www.boost.org/doc/libs/1_35_0/doc/html/hash/combine.html
template <typename T>
inline void hash_combine (std::size_t& seed, const T& val)
{
    seed ^= std::hash<T>()(val) + 0x9e3779b9 + (seed<<6) + (seed>>2);
}

// auxiliary generic functions to create a hash value using a seed
template <typename T>
inline void hash_val (std::size_t& seed, const T& val)
{
    hash_combine(seed,val);
}
template <typename T, typename... Types>
inline void hash_val (std::size_t& seed,
                      const T& val, const Types&... args)
{
    hash_combine(seed,val);
    hash_val(seed,args...);
}

// auxiliary generic function to create a hash value out of a heterogeneous list of arguments
template <typename... Types>
inline std::size_t hash_val (const Types&... args)
{
    std::size_t seed = 0;
    hash_val (seed, args...);
    return seed;
}

#endif

2. UnorderedSetTest.cpp

#include <unordered_set>
#include "../../Core/print.hpp"
#include "UnorderedSetTest.h"
#include "../../Core/hashval.hpp"
#include "../../Domain/Models/Customer.h"
#include "../../Domain/Models/CustomerHash.h"
#include "../../Domain/Models/CustomerEqual.h"
#include <string>
#include <iostream>

using namespace std;

void UnorderedSetTest::simpleHashFunc()
{
    // unordered set with own hash function and equivalence criterion
    unordered_set<Customer, CustomerHash, CustomerEqual> custset;

    custset.insert(Customer("arne", "wink", 70));
    custset.insert(Customer("peter", "zhang", 70));
    PRINT_ELEMENTS(custset);

    Customer cust = Customer("arne", "wink", 70);
    if (custset.find(cust) != custset.end())
    {
        cout << "Customer: " << cust << " found!" << endl;
    }
    else
    {
        cout << "Customer: " << cust << " not exists!" << endl;
    }

    Customer cust2 = Customer("arne", "wink2", 70);
    if (custset.find(cust2) != custset.end())
    {
        cout << "Customer: " << cust2 << " found!" << endl;
    }
    else
    {
        cout << "Customer: " << cust2 << " not exists!" << endl;
    }
}

void UnorderedSetTest::run()
{
    printStart("simpleHashFunc()");
    simpleHashFunc();
    printEnd("simpleHashFunc()");
}

3. 运行结果:

---------------- simpleHashFunc(): Run Start ----------------
[arne,wink,70] [peter,zhang,70]
Customer: [arne,wink,70] found!
Customer: [arne,wink2,70] not exists!
---------------- simpleHashFunc(): Run End ----------------