C++ Unordered_map Library - unordered_map() Function

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Description

The C++ function std::unordered_map::unordered_map() constructs an unordered_map with copy of each elements present in existing unordered_map.

Declaration

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

C++11

unordered_map(const unordered_map& um);

Parameters

um − Another unordered_map object.

Return value

Constructor never returns value.

Time complexity

Linear i.e. O(n) in average case.

Quadratic i.e. O(n²) in worst case.

Example

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

#include <iostream>
#include <unordered_map>

using namespace std;

int main(void) {
   unordered_map<char, int> um1 = {
            {'a', 1},
            {'b', 2},
            {'c', 3},
            {'d', 4},
            {'e', 5}
            };

   unordered_map<char, int>um2(um1);

   cout << "Unordered_map contains following elements" << endl;

   for (auto it = um2.begin(); it != um2.end(); ++it)
      cout << it->first << " = " << it->second << endl;

   return 0;
}

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

Unordered_map contains following elements
e = 5
a = 1
b = 2
c = 3
d = 4