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
unordered_map.htm
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