C++ Unordered_map Library - hash_function() Function

Description

The C++ function std::unordered_map::hash_function() Calculates the hash function object used by the unordered_map container.

The hash function is a unary function that takes an object of type key_type as argument and returns a unique value of type size_t based on it.

Declaration

Following is the declaration for std::unordered_map::hash_function() function form std::unordered_map header.

C++11

hasher hash_function() const;

Parameters

None

Return value

Returns the hash function.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::unordered_map::hash_function() function.

#include <iostream>
#include <unordered_map>

using namespace std;

int main(void) {
   unordered_map <string, string> um;

   auto fun = um.hash_function();

   cout << "Hash function for a = " << fun("a") << endl;
   cout << "Hash function for A = " << fun("A") << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Hash function for a = 4993892634952068459
Hash function for A = 6919333181322027406

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