C++ Unordered_map Library - swap() Function

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Description

The C++ function std::unordered_map::swap() exchanges the content of first unordered_map with another.

Declaration

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

C++11

template <class Key, class T, class Hash, class Pred, class Alloc>
void swap( unordered_map<Key,T,Hash,Pred,Alloc>& first,
           unordered_map<Key,T,Hash,Pred,Alloc>& second);

Parameters

• first − First unordered_map object.

• second − Second unordered_map object of same type.

Return value

None

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::unordered_map::swap() 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;

   swap(um1, um2);

   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