unordered_multiset hash_function() function in C++ STL

Last Updated : 02 Aug, 2018

The unordered_multiset::hash_function() is a built-in function in C++ STL which is used to get the hash function. This hash function is a unary function which takes a single argument only and returns a unique value of type size_t based on it. Syntax:

unordered_multiset_name.hash_function()

Parameter: The function does not accepts any parameter. Return Value: The function returns the hash function. Below programs illustrate the unordered_multiset::hash_function() function: Program 1:

CPP

// CPP program to illustrate the
// unordered_multiset::hash_function() function

#include <iostream>
#include <string>
#include <unordered_set>

using namespace std;

int main()
{

    unordered_multiset<string> sampleSet = { "geeks1", "geeks1", "for", "geeks2" };

    // use of hash_function
    unordered_multiset<string>::hasher fn = sampleSet.hash_function();

    cout << fn("geeks") << endl;

    for (auto it = sampleSet.begin(); it != sampleSet.end(); it++) {
        cout << *it << " ";
    }
    cout << endl;

    return 0;
}

Output:

15276750567035005396
geeks2 for geeks1 geeks1

Program 2:

CPP

// CPP program to illustrate the
// unordered_multiset::hash_function () function

#include <iostream>
#include <string>
#include <unordered_set>

using namespace std;

int main()
{

    unordered_multiset<string> sampleSet;

    // use of hash_function
    unordered_multiset<string>::hasher fn = sampleSet.hash_function();

    cout << fn("geeksforgeeks") << endl;

    return 0;
}

Output:

5146686323530302118

gopaldave

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