unordered_set hash_function() in C++ STL (original) (raw)

Last Updated : 5 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:

unorderedsetname.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 #include #include

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 #include #include

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)