Last Updated : 05 Jun, 2023
The unordered_set::hash_function() is a built-in function in C++ STL which is used to get hash function. This hash function is a unary function which takes asingle argument only and returns a unique value of type size_t based on it.
Syntax:
unordered_set_name.hash_function()
Parameter: The function accepts no parameter.
Return Value: The function returns the hash function. Below programs illustrate the unordered_set::hash_function() function:
Program 1:
CPP
// CPP program to illustrate the
// unordered_set::hash() function
#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;
int main()
{
unordered_set<string> sampleSet = { "geeks1", "for", "geeks2" };
// use of hash_function
unordered_set<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 geeks1 for
Program 2:
CPP
// CPP program to illustrate the
// unordered_set::hash() function
#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;
int main()
{
unordered_set<string> sampleSet;
// use of hash_function
unordered_set<string>::hasher fn = sampleSet.hash_function();
cout << fn("geeksforgeeks") << endl;
return 0;
}
Output:
5146686323530302118
Time complexity: O(1)
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